NOTES ON OPTICAL CALCULATIONS NEWNES · International Electronics, 7 -valve, 3 wave-band, covering 16-400 metres. Latest Brimar single -ended valves, variable BFO, Stand-by switch,

NOTES ON OPTICAL CALCULATIONS

NEWNES

OR .

FEBRUARY 1948

44.

AN ELECTRIC FLOOR LAMP. FOR CONSTRUCTIONAL DETAILS (See page 163)

CON TEN Ts

Making a Pinhole Camera

Davy or Stephenson ?

Electrical Notes

Magnetic Sound Recording

Stone Polishing for Amateurs

Electric Water Heating

World of ModelsTrade Notes

Cyclist Section

A CUP FORDRAWING BOARDS

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February, 1948 NEWNES PRACTICAL MECHANICS 145

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146 NEWNES PRACTICAL MECHANICS February, 1948

I.C.S. TRAINED MENare in Greater Demandthan Ever-Maximum productiondepends on high technical skill, suchas that acquired by I.C.S. Students

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148 NIENVNES PRACTICAL MECHANICS February, 19 48

RADIO GEAR for ALL AMATEURSCOMMUNICATIONS RECEIVERS. International Electronics, 7 -valve, 3 wave-band, covering 16-400 metres. Latest Brimar single -ended valves, variable BFO,Stand-by switch, RF and LF gain. Self-contained speaker, giving excellent volume.Fine signal-to-noise ratio. A.C. mains 190-260y. Guaranteed 12 months. 34 gns.

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PREPARE FOR COMPETITION -NOW!As the Engineering Industry swings into its normal stride, the inevitable competitionfor the secure and well -paid posts will return. It is the man who stands out from therest because he is technically trained who will be in the happy position of taking overthe more responsible, more secure, and better paid positions. " ENGINEERINGOPPORTUNITIES " will show you how to get this all-important technical trainingquickly and easily in your spare time. This 100 -page book is full of valuable informationand explains the simplest way of preparing for recognised Examinations. Among thecourses described are :

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Owing to the paper shortage "The Cyclist," "Practical Motorist," and "Home Movies " aretemporarily incorporated.

Editor : F. J. CAMM

VOL. XV FEBRUARY, 1948 No. 172

BY THE EDITOR

About Time and TimepiecesTHERE is a never-ending fascination about

clocks, watches, and other devices formeasuring the passage of time. These

go back to the very earliest days of whichman has record. The Chinese probablyinvented the first form of clock, the Clepsydra,or water -clock, consisting of a container filledwith water with a float. The water wasallowed to drip from a small orifice, and as thefloat descended with the diminishing level ofthe water, a cord wound round a rod andattached to the top of the float caused a handto record the movement on a dial.

Many modern copies of the Clepsydra havebeen made for demonstration purposes, andthey can be made to keep reasonably closetime. Sundials and graduated handles wereintroduced by the Greeks from the Romans.

The earliest astronomers observed that theearth took a year to make a revolution roundthe sun, and one day to make one revolutionround its own axis.

Julius Cxsar was the first to attempt toconstruct a calendar which would tally withthe sun's year, and he decided on a year,divided into twelve months, or a year theodd months having 31 days and the even 3o,with the exception of February which was tohave 29, and 3o every fourth year. It iscommon knowledge that the year consists of365i days. The quarter of a day is ignoredexcepting during Leap Year, when it is addedto the month of February. July took its namefrom Cresar's christian name, the monthof Julius.

However, the Roman Emperor Augustus,who was born in the eighth month, thoughtthat one of the months should be named afterhim, so he borrowed February's 29th day andadded it to August, thus bringing Februaryto 28 days.

It was not until 1,50o years later that it wasdiscovered the Julian system resulted in aloss of 11 mins. to secs. every year ; thus bythe year 1532 there was a deficit of t 1 days,and to remedy this is days were dropped fromthe year 1532 and a new calendar wasestablished which was lengthened by 5hrs.49 mins. This calendar was introduced byPope Gregory XIII, and it is known as theGregorian Calendar. He decided that ratherthan add the awkward figure of 5 hrs. 49 mins.to the year, he would add an extra day every300 years.

England followed this example, and onSeptember znd, 1752, there was a gap of xidays, and people went to bed on September2nd to awake on September 14th. It was in1752 that January 1st was established asNew Year's Day.

It is a popular belief that Leap Year is everyyear that is divisible by four, but the year 1900was not a Leap Year, although the year 2000will be.

Of course, by adding a day every fourth yearin the course of a century we have addedalmost a day too much, and therefore thecentury years which are divisible by tooare not Leap Years unless they are alsodivisible by 400.

First Mechanical ClockIT was not until the 14th century that theI first mechanical clock was constructed.Although the name ofit is certain that it was until 1872 in thetower of Dover Castle. It was probably madein about 1395, and may be seen working inthe Science Museum, South Kensington. Itsconstruction is of great interest, because itpaves the way for the early watch escapement.All of the clocks and watches until 175o werefitted with an escapement similar to that usedin the Dover clock, and known as the Verge.

In it the balance -arm or foliot was notfitted with a spring, but carried two heavy leadblocks which swung through an angle of about90 deg. under the action of the escape -wheel.

It was in 567o that Huygens adapted thependulum to the control of clocks. Theproperties of the pendulum had been dis-covered about 1620 by Galileo while com-paring the swinging of a lamp pendulum withthe beating of his pulse during a service inPisa Cathedral. He discovered that isochron-ism (or equal time periods) of a pendulum isapproximate only, and is only exact when thearc remains constant. The Verge escapement,the only one then known, demanded an arc ofat least 6o deg., and the timekeeping thereforewas not good.

Dr. Robert Hooke invented the anchorescapement in 1675, and this made it possibleto use a pendulum which swung through asmall arc only and thus enabled greatertimekeeping accuracy to be obtained. It wasHooke who also discovered the law relatingthe action of forces with the deflection ofsprings, and he also discovered the couplingfor shafts which are not' in line known asHooke's joint, or the universal joint.

The early clocks were invariably driven bymeans of a weight, and it was the inventionof the mainspring by Peter Henlein of Nurem-burg at the end of the 15th century that madepossible the construction of a watch. Thefirst watch escapements were of the Vergetype, and the amount of space occupied bythis escapement caused the watch to be almostspherical in shape, which resulted in them

being called Nuremburg Eggs. They werenot accurate timekeepers.

There are plenty of specimens of Vergeescapement watches still in existence, andthey may be picked up quite cheaply. Theyare, of course, beautifully made, but mosterratic and inaccurate timepieces.The " Fusee "In an effort to improve their timekeeping

by providing a constant torque, a deviceknown as the fusee was invented about 1525.It is still used in some clocks to -day and in afew pocket chionometers. In this devicethe mainspring is contained in a cylindricaldrum or barrel on which is wound a lengthof slender chain. The other end of the chainis wound on a spiral drum, so contrived thatas the spring runs down and becomes weakerthe leverage on the axis of the spiral becomesgreater, thus giving a practically constanttorque throughout the range of the spring.In many respects, however, it was found thatthe fusee was a fallacy for accurate time-keeping, which does not depend so much uponan equal torque as upon the isochronism ofthe escapement ; that is to say, when the watchor clock is fully wound and the balance hasa greater arc of movement the time of eacharc should be exactly equal to the short arcwhen the watch is nearly run down. It alsodepends to some extent upon the compensa-tion of the balance, to correct temperaturechanges. When the temperature of a watchis raised the hairspring lengthens, becomesweaker and the watch tends to lose. Tocorrect this the balance is made bi-metallic,and under the influence of heat tends tobecome smaller in diameter. As it thus hasa smaller radius of gyration, it will tend togo faster and so compensate for the weaknessof the hairspring.Elinvar Hairsprings

To -day, in very high-class watches, elinvarhairsprings are used. This metal has thepeculiar property of being practically un-affected by heat.

It was Hooke who invented the hairspringin x66o. It gives the balance a definiteperiod of oscillation. The first big improve-ment in escapements, was made by GeorgeGraham in 1725, with his cylinder escape-ment. This is now practically obsolete, forit still did not attain the perfection sought.Mudge invented the detached lever escape -merit, and with modifications this is the formof escapement almost universally employedto -day. A few chronometers are made withdetent escapements, in which a lever is notused.-F. J. C.


Developments in MagneticSound Recording

A Meeting of the B.S.R.A.Reported by DONALD W. ALDOUS, M.Inst.E.

AT a recent meeting of the British SoundRecording Association in London,Mr. P. T. Hobson (of Boosey &

Hawkes, Ltd.), delivered a lecture ondevelopments and present-day applications ofmagnetic recording, with special reference toythe wire system.

Dr. L. E. C. Hughes, president of theB.S.R.A., was in the chair, and in his intro-duction he made a brief reference to thehistorical aspect of the subject. He men-tioned that the principles of "magneticrecording have been known for more than40 years, as Valdemar Paulsen, the Danishscientist, demonstrated his " Telegraphone "at the Paris Exposition in 1900, and in thesame year Poulsen obtained U.S. Patent No.661,6t9 for steel tape as a recording mediumor carrier. A model of the early Paulsenwire recorder can be found in the ScienceMuseum, South Kensington.

Mr. Hobson, in his opening remarks,explained that there was no importantadvance in this method until the advent ofthe thermionic valve amplifier and the pro-duction of suitable steel tape. These.resultedin the introduction of the Blattnerphone(named after the late Ludwig Blattner) andits improved successor, the Marconi-Stillerecorder, both using steel tape, the former

The Boosey & Hawkes studio model recorder, Type S.1,is designed for high -quality music recording.

being first used in this countryby the B.B.C. in 193o.

The MagnetophonIn Germany an instrument

known as the Magnetophon wasdeveloped and marketed byA.E.G. of Berlin several yearsbefore the war, primarily as adictating machine. During thewar intensive research producedmarked improvements in per-formance, and the quality of re-production now obtainable is ofa high order. The two prin-cipal novel features are : (a) theuse of supersonic frequencyA.C. for biasing (i.e., pre -magnetising) as well as for wip-ing (i.e., erasing the signal), and(2) the use as a recording med-ium of a tape the magnetisablelayer of which consists of a dis-persion of iron -oxide particlesin a plastic material (usuallyacetyl -cellulose or polyvinyl -chloride).

The difficulty that had, sincethe beginning of the century,

impeded progress was theview accepted by science ofthe magnetisation processitself. Research by theArmour Research Founda-tion, of the Illinois Insti-tute of Technology, Chic-ago, particularly the workof the young Americanengineer Marvin Camras,and later through experi-ments in this country, hadrevealed a much clearerpicture of the requirementsof the material for wirerecording, and on applyingthe results to the design ofpractical machines, mag-netic recording on wire hadbeen raised to the high -quality class, as Mr. Hob-son proved by a demonstra-tion of specimen recordings.

Stainless Steel WireThe clue to the realisa-

tion of practical equipmentwas in the wire. A stain-less steel wire of 4 mils.diameter had finally beenselected, and the standardspeed for quality reproduc-tion is 24in. per second.The standard playing -timeis 66 minutes, which couldbe increased if a lowergrade of speech quality isacceptable. Longitudinalmagnetisation is used, andthe wire runs through acarefully designed head. Ifthe wire should break, aknot could be tied, the endstrimmed and the jointwould pass safely over achannel in the head.

The new British wire recorder, the Model "A" Boosey& Hawkes unit, intended for speech recording.

The process of magnetisation induced amultitude of disc -like magnets, face to facealong the length of the wire, of a thicknessdepending on the wavelength. The de-`,.magnetisation effect was of paramount significance, as it determined the losses for a givenwire speed and maximum frequency of therecording currents because of the self -erasingeffect of the high demagnetisation in shortmagnets, here related to the constant diameterof the wire.

A demagnetisation curve of a sample ofmaterial, used to indicate the relation betweenH and the resulting B, showed the relationbetween the applied field H and 4 7r I, whereI was the intensity of magnetisation. Thecurve revealed the applied field which wasnecessary to reduce the coercivity to zero;and this value determined the effectiveness ofthe material as a permanent magnet.

The term coercivity covered two concep-tions : the inductive coercivity, which wasthe field required to reduce the remanentinduction to zero, and the intensity coerci-vity, which was the field required to reducethe intensity of magnetisation to zero. Thisdistinction was not of importance, how-ever when permanent magnets rarely hadtotal coercivities greater than too oersteds,because below that figure there was prac-tically no difference between the two.

Magnetic InductionAfter this exposition of the magnetisation

process, Mr. Hobson explained that it wasthe magnetic induction in the wire thatgenerated a reproducing voltage, and evenif the self -demagnetisation was complete,there still remained some intensity of mag-netisation which was only entirely removedif the total demagnetising field was increasedto the intensity coercivity of the material.

If a line was drawn from the origin to.the demagnetisation point on the B: H curve(hysteresis loop), it was found that the

February, 1948

tangent of this line to the vertical,D, was directly related to the ratio of thewavelength to the diameter, and thus tofrequency. Hence, for the purposes ofsound reproduction, it can be shown that:Loss in db. (decibels) = 20 log.R/(R + D),where R is the ratio of inductive coercivityto remanent induction, which dependedexperimentally on the material, and it hada limit of unity.

The wire for the original machines hada remanence of 6,000 to 7,000 gauss, andrequired a speed of 5ft. per second forspeech when employing an available stainlesssteel wire, with a coercivity of 6o to 90oersteds. It had now been shown that thehighest inductive coercivities at the expenseof remanence were needed, and these require-ments were met in a completely annealedaustenitic steel which, because of the neces-

NEWNES PRACTICAL MECHANICS

sary heat treatment, was substantially non-magnetic, the remanence being 600 gaussand coercivity 300 oersteds. This type ofwire was now in production in GreatBritain, with continuous monitoring andautomatic control of the hysteresis loop ona cathode-ray tube as -the annealing currentwas passed through the wire.

The use of a high amplitude biasing orpolarising current was usually thought to beessential in overcoming the bend in theinitial magnetising curve when recording,but Mr. Hobson outlined a more funda-mental approach according to the Weissdomain theory of magnetisation.

Noise AnalysisNoise analysis is complex, commented

Mr. Hobson, as there are several types ofnoise contributing to the total output ; for

153

example, virgin noise (i.e., as the wire comesfrom the drawing machine), dynamic back-ground noise from the recording bias, staticbackground noise from erased recordings,and a modulation noise component, but asone of the chief noise sources is proportionalto the remanence it is possible to obtain alow noise level corresponding to a signal/noise ratio of 6o decibels.

The speaker revealed, in conclusion, thatthe British version of the American ArmourModel 5o wire recorder, which was exten-sively used during the war by the Services,both in the air and on the ground, wasnow in production, and a few units wereavailable strictly for speech and non -enter-tainment applications costing around £147.Fidelity models for music recording werenow being developed, and it is hoped theywould be marketed in about a year.

Electric Light and PowerInstallation -3

House Circuits Conduit Sizes : Looping -in Wiring System.

THE main cables of all installations areled to a main distribution board, andfrom there the current is distributed

to the various localised centres which maybe on different floor levels.

Local distribution boards are placed asnear as possible in the centre of .the areathey serve. From the local boards conduc-tors radiate to various branch circuits. Eachof these circuits will feed a number of light-ing and/or power points. The number ofpoints is usually limited to not more thanten on one fuse. In case of a short circuitblowing a fuse the least number of pointsput out of action the better ; it is also easierto locate the source of trouble.

House CircuitsOrdinary private house installations usu-

ally have only one distribution board, or. box,with fuses on both poles of each circuit. Acircuit feeds all the points on one floor only,so 'that it is quickly known which fuses haveblown without having to withdraw all ofthem for inspection. Incidentally, the fusebox should have a diagram inside the lid,showing the position of the fuses for eachfloor. Unfortunately, most small installa-tions have only one switch serving the dis-tribution board. A first-class installation willhave a switch for each circuit. A fuse shouldnot be changed without switching off, for itis not safe for an amateur to tamper with alive circuit.

Capacity of CablesAll electric cables develop heat when a

current is passing through them. As thetemperature -rises the resistance of the wire tothe passage of the current becomes greaterand this causes a loss of voltage.

The safe current carrying capacity of acable, in amperes, is proportional to its crosssection. It must be of such a size that therise of temperature is not appreciable whencarrying a maximum load. , In lighting cir-cuits a very small fall in potential makes aconsiderable difference to the illuminatingpower of the lamps.

On long main feeders the cross section area

(Continued from page 87, December issue.)

is calculated to give a minimum voltage drop.It is the general practice to instal cables oflittle greater capacity than is necessary .tocarry the possible maximum load. Too lib-eral an allowance in this respect will add veryconsiderably to the cost of cables and othermaterials. There are also other importantfactors that require consideration.

Standard Loading CapacityStandard maximum loading has been fixed

by the rules of the Institution of ElectricalEngineers. The amount of current that canbe safely carried by a cable depends on thecross section area of the wires, and the riseof temperature within safe limits. Heat thatis developed in a cable is dissipated to thesurrounding atmosphere through the insulat-ing material. Much, therefore, will dependon the composition and thickness of the in-sulation, and, in turn,the thickness of theinsulation depends on thevoltage of the system.

A metal conductor(copper in most cables)of small cross sectionarea has proportionatelygreater surface area thana thick conductor. It has,therefore, a proportion-ately superior heat dissi-pating area. Within cer-tain limits, a thin con-ductor can safely carry ahigher current densitythan one of greater crosssection.

Standard cable loadingsare calculated to carry "amaximum current with aminimum voltage droptaking all the foregoingfactors into consideration.

The following tablegives a range of suitablecables to carry from 5 to37 amperes.

MainsSwitch

By S. T. CORNER

CURRENT -CARRYING CAPACITIES OFCONDUCTORS

Carrying Approx. lengthNumber Diameter capacity in feet (lead

of of Wire in amperes and return) forStrands (in.) I.E.E. 1 volt drop by

Rules I.E.E. Rules

I .044 i . 5 363 .029 5 473 036 to 357 .029 15 347 .o36 24 337 .044 31 ' 397 .052 37 45

Conduit Sizes .

Before wiring an installation it is mostimportant to determine the size and thenumber of wires to be run. This will dependon the system of wiring adopted, which willbe dealt with later. The number of cablesto be run determines the size of the conduit.If the correct size of tubing is used no diffi-culty will be experienced in drawing in the

Mains

Fig i3. Diagram of looped -in wiring system.

Looped- /n Wiring

Back Of Two Way

Switch Board ShowingLeads From Each Pole

154 NEWNES PRACTICAL MECHANICS February, 19 48

wires and easing them from one bend toanother, or from a tee piece or elbow to thetube ends.

Wiring is always a two -man job ; one isneeded on the draw wire while the other feedsin and eases the wires around bends to pre-vent damage to the insulation. Should thecables be too tight a fit in the tubing theinsulation may be damaged and the wiresstretched or even broken. Powdered frenchchalk, sprinkled on the insulation, may beused as a lubricant to assist when drawingin. Anything of the nature of grease or oilmust not be used in any circumstances ; theinsulation would be ruined.

The following conduit wiring table maybe taken as a general guide for tube sizes.

CONDUIT WIRING TABLEGiving approximate number of cables that tubes

can contain.

CableSize

Light GaugeSize of Tube

Heavy GaugeSize of tube

1/0443/0293/0367/0297/0367/0447/064

fin. fin. fin. sin. fin. fin. I in. tin.

6 10I 4 5I 3 4- 2 3 7

2 3 6

- I 2 4I I 2

98

2 ,3 5I 3 4- 2 4- I 3 5- I 2 5- - - 4- - 2

888

Circuit WiringThe wiring from the circuit distribution

boards is much smaller than that used forthe main cables. As a general rule light-ing circuits are divided up so that eachcarries a maximum load of about threeamperes ; the wiring is actually calculated tocarry five amperes. There is an alternativechoice of two types of cable, viz., singlestrand 0.044 gauge, or three strand 0.029gauge, known in the trade as 1/.044 and3/.029 respectively. Stranded wires, beingmore flexible, are preferable to the single wiretype.In good modern wiring work the use ofjointed wire is strictly taboo, -and in nocircumstances is a jointed wire drawn intoa tube. 'Where a joint is unavoidable, forany particular reason, it is made in a specialjoint box or a junction box. Unsoldered, ordry joints, are barred at all times. No matterhow carefully they may be made corrosion issure to develop in time ; this will set up a,high resistance that will generate heat, whichmay cause fire. There are occasions whena jointed wire is unavoidable, but it mustalways be soldered, and well insulated witha rubber sleeve and insulating tape.

Cut-outs and FusesEvery electric circuit is protected by a cut-

out device to prevent damage to the wiringby over -heating if a sudden overloading or ashort circuit occurs ; it also protects thelamps, motors, and instruments in the cir-cuit. At the power station the mains areprotected by automatic cut-out devices thatbreak the circuit by dropping out the mainswitches. Similar devices are used for high -power motors. Ordinary house circuits areprotected by main fuses fitted between themain switch and the distribution board, andeach of the auxiliary circuits has a pair offuses.

House fuse boards are usually installed ina cupboard under the stairs, or in an incon-venient position in a pantry. It is very badpractice to place a fuse board high up over adoor where fuse renewal is difficult in anemergency. At the same time, the fuseboard must be kept out of reach of children,or placed where it is not likely to attractattention as a possible plaything. Wherethis danger exists an ironclad fusee box issafest, with 'a lid secured by screws; Or asafety device which prevents lid from beingopened until the switch is off.

The fusible wire cut-out is, of 'course,

simplest and cheapest. It is a well-knowndevice consisting of a detachable porcelainhand -grip fuse holder with two slip -in ter-minals that fit into spring -clip terminals onthe base of the fuse -holder. To the ter-minals of the base are connected the incom-ing main cable and the outgoing circuit wire,respectively. Between the two slip -in ter-minals of the fuse holder is a wire of copper,tin or lead of a thickness sufficient to carryan electric current of pre -determined value.

Safety Fuse -holdersFuse -holders of the safety type are those

with a tube or a channel through whichthe fuse wire passes from one terminal to theother. Whether for quickness or ease, thefuse wire must not be made to by-passthe proper course. The tubular type servesa double purpose ; when a fuse blows themolten metal is retained in the enclosure andprevented from causing damage or fire ; andthe violence of the rupture induces heated airto rush out of the tube and break the arc asthe circuit is opened.

Junction Box Suitable ForTough Rubber Cables.

Junction Box Suitable ForLead Covered Cable

Fig. t4.-TWO types of junction

All fuses are fitted between the switchesand the lighting and power circuits, so thatthe current can be switched off before a fuseis renewed. A fuse acts as the weakest linkig the chain, which will break before an over-load can do damage. Normal lighting cir-cuits are usually wired to carry five amperes,but are loaded to about three amperes. Gen-erally a five -ampere fuse wire is used. Cir-cuits carrying variable loads, such as thosethat feed electric motors, which normallytake a heavy starting current, have fuses thatblow at as much as too per cent. above therated current intake of the motor.

Looping -in Wiring SystemMost, in fact it might be said all, modern

lighting circuits are wired on the " looping -in." system. This method has the advan-tage of being easy to run without having tomake a multiplicity of joints, or use of agreat number of joint boxes. Wires of twodifferent colours are used to facilitate recog-nition at the connecting ends. The red

wires are carried to the switches and theblack to the lamps. Red, or switch, wiresare connected to the live side of the circuit.

Referring to Fig. 13, it will be noticedthat the feed wire is taken to the live sideof the first switch and then looped out andcarried to the live side of the next switch,and so on in unbroken succession. The wiresare of necessity cut at the switch and theends twisted together, but the joint is a safemechanical one secured by the switch term-inal screw. Provided the screws are tight,there is little fear of corrosion. From theother terminal of the switch another red wireis taken to one of the lamp -fitting terminals.

The black wire from distribution boardis carried to the first lamp fitting and fromthere looped out and taken to the next lampfitting, in exactly the same way as the switchwires are run. Each lamp terminal acts asa mechanical joint fitting which is electric-ally sound, and is in a safe and convenientposition within the fitting itself.

The great advantage of the " looping -in "system is the absence of intermittent joints.

When it is necessary totest out an installation,or to trace a fault in thewiring, the positions ofall the joints are known.It is necessary only toopen up or remove afitting to get at the bareend of a lead and con-nect a testing instru-ment.

Junction BoxesLooping -in is not

always so simple as itmay appear from theforegoing description ;runs- are not ideallystraight, nor devoid of

complications, and it is frequently necessaryto use junction boxes, two examples of whichare shown in Fig. 14. The junction box" A " has a specidl type of terminal whichmakes a sound mechanical joint. The boxitself, being made of metal, provides for the'continuity of the earthing system of the tub-ing. Box " B " is suitable for lead -coveredcable being provided with earthing clips thatgrip the metal sheath. The base of the boxin this case is also of metal. Junction boxesof plastic material do not provide continuity,and when these are used the outer sheaths ofthe cables are connected by a bare copper wire,preferably run round the outside of the fitting.

On small installations a considerableamount of tubing and cable can sometimes besaved if the main leads are taken to a cen-trally situated junction box, and froth therethe looping runs carried to the variousswitches and light points. Various switchingsystems call for additional wires or a differ-ent arrangement of the looped -in wires. Thesewill be dealt with in a later article.

(To be continued.)

1111111111111111

BOOKS FOR ENGINEERS........:..................ScrewThread Tables, SI-, by post 513.

Refresher Course in Mathematics, 816,by post 9!-.

Gears and Gear Cutting, 61-, by post 616.

Workshop Calculations, ' Tables andFormulae, 61-, by post 616.

Engineer's Manual, 1016, by post

Plant Engineer's Pocket Book, 6/-, bypost 616.

Newnes' Metric and Decimal Tables, 3/6,by post 319.

Wire and Wire Gauges (Vest PocketBook), 316, by post 3I9.

Screw Thread Manual, 61-, by post 616.

Newnes' Engineer's Reference Book, 421-,by post 431-.

Practical Mechanics' Handbook, 1216, bypost 131-.

Published by

GEORGE NEWNES, LTD., TOWER HOUSE,SOUTHAMPTON STREET, STRAND, W.C.2

4


Stone PolishinA for AmateursA Simple Explanation of a Fascinating

WHEN you visit any of our seasideresorts a close scrutiny of the sandsand shingle may reward you with

what is usually terrrred a " pebble, thoughnot always will it have that rounded four;we associate with the word.

Pebbles may be recognised by their trans-lucency and colour, and most commonly areforms of silica to which such names as agate,cornelian, jasper and chalcedony are applied.They include also cairngorm and amethyst,though these two are local and rare. Thesouth and east coasts are happy huntinggrounds for the pebble hunter.

Now, having found your pebble, you willwant to cut it, in other words, to reduce itto a regular shape and give it polish to bringout its colour and markings.

Tools RequiredJust what tools are required will depend

upon what is to be done with the stones.

Fig. 3. - This arrange-ment, using an Archimedeandrill, can also be adopted.

B

Fig. 1.-(Above). T h eapparatus used in stonepolishing. Fig. 4.-(Right)The stone should be cementedto a short handle whenthe lapping board is used

in the lathe.

If it be desired to only grind and poliih asingle face to bring out the colour and mark-ings, very simple appliances will serve. Therough grinding will be done on a grindstoneor emery wheel, if either is available ; ifnot, then the more arduous process of rub-bing down by hand on a slab of sandstone,or wood charged with coarse carborundumpowder and .water, is the next best way.

Having ground the stone to a fair surface,free from pits and other blemishes, the next

Process

thing is to repeat the process with a newtool and a finer grade of carborundum, untilthe surface shows no sign of scoring andtakes on a surface that may be comparedwith ground glass.

The Polishing ProcessIt will then be ready for polishing, which

may be done on a pad of felt tacked. to aslab of wood and charged with putty powderand oil. The polishing process demandspatience, and must be continued until thepolish remains after the surface has beenwashed free of oil: If the utmost brilliancybe desired, the polishing may be continuedwith jewellers' rouge on a surface of pitch,using the rouge wet, but allowing it to be-come nearly dry as the process approachescompletion.

Should the stone be of such a shape or sizethat it cannot be held in the hand, it may becemented to a block of wood, so as to givea better hand -hold.

Mounting the StonesStones polished in this way have a certain

amount of interest as mineral specimens, butthere is no very useful purpose to which theycould be applied. If it be desired to mountthe stones either in jewellery or as surfacedecoration, say, to a box lid, then the polish-ing process must be adapted to the produc-tion of a regular convex surface. This maybe done by the use of the simple appliancesillustrated.

Fig. r shows a spindle made from dowellingon the centre of which a cotton reel withbore enlarged is fixed ; at top a wire nail isdriven in, the head cut off and the nail filedto a rounded point. The pebble is cementedto, the other end of the spindle as shown.A knob handle, shod with a plate of brassin which a central socket is drilled, must bemade, as shown at A. This spindle is rotatedwith a bow, pressure being put on with, thehandle held in the left hand, whilst thepebble is sunk in a hollow gouged in the slabof wood B, carborundum being used as theabrasive. It is with this simple appliancethe lapidaries of India cut and polish theirgems. Fig. 2 shows the process in operation.

An Archimedean DrillIf the worker has an ordinary drill stock

with expanding chuck, the arrangementshown in Fig. 3 might be adopted withadvantage. The stone is cemented to a shortpiece of dowelling, into which a stout screwis driven and its head cut off with the hack-saw.

Grinding and Polishing PebblesThose who possess a lathe may use it for

the grinding and polishing of pebbles, chuck -

Fig. z.-The polishing process in ope: crion.

ing the wood block B, Fig. s, and mountingthe pebble on a short handle as shown inFig. 4, but they must be warned not to allowthe abrasive to get into the lathe bearings.

The process obviously can be better con-ducted with the lapidaries' wheel, whichrotates horizontally. This tool may beadapted also to slitting and faceting stonesand, in fact, to every process connected withthe cutting and polishing of precious andother stones.

Science Notes.High-speed PhotographyT LIKE to remind my friends that they are-I- unintentionally scientific. You cannotspend a day without using science. If, whichheaven forbid, you play golf, you must rea-lise that high-speed cinema pictures havebeen employed to record the flight of balls,that instruments which would show the bend-ing of a half -inch plank under the weight ofa fly have helped to balance the ball, or thata most expensive mechanism has preparedyour club and the green.

If you go to the cinema, remember thathigh-speed photography has shown that gas=jiving fast can break glass and that it isonly the poorness of your eye which preventsyou from discovering that you sit in darknessevery time each " frame " changes. That is,of course, when successive photographs arethrown upon the screen.Paper SaucepansIF you take a paper jar such as is used for

ice cream or milk you can easily boil waterin it ; this may be used commercially one day

By A. M. L

to save washing-up. Washing-up machinesare not good, badly as they are needed, iftheir setting up takes more time than thewhole operation.

To return to the paper saucepans, you cansoon prove to yourself that water conductsthe heat away through thin paper so quicklythat the paper will not catch fire. If thepaper is doubled so that the air is trappedbetween the layers it will act as an insulatorto both sound and heat. Many cinematheatres are equipped with absorbents madeof cellular paper.Radiated Energy

Thick or folded paper will burn, simplybecause the heat cannot get through it quicklyenough and so the temperature rises. Heat,by the .way, radiates through the ether likelight although it has a far longer wavelength.The radiated energy from the sun actuallypresses upon the earth to a total extent ofabout 75,000 tons. Heat hits you, in truth,as well as phrase.


Electrical NotesA Discussion on Various Electrical Problems of General Interest

UCH argument sometimes arises con-cerning earthed mains, or 'potential" to earth," etc.

For instance : In the 200 v. insulatedD.C. system Fig. i (a), is one main zoo v.1`,1,above," and the other 200 V. " below"earth pOtential ? If so, should not thepotential -difference across the pair be 200 V.1-(-200 v.)=400 V. ? If the ' system wereperfectly insulated, would it be possible toreceive a shock from either line, standing onearth ?

One does occasionally hear wrong reasonsfor earthing D.C. or A.G. distribution systems.Would there be any advantage- whatever inconnecting solidly to earth'orte of the lines inFig. 1 (a) ?-to take the simplest example.

The answer is none, as far as any safetyrequirement is concerned. In fact, therewould be some disadvantages.

Voltage " To Earth "The " earth return " is still with us in

railway traction. It effects a saving, of course,but a second ".earth " on the insulated linemeans a shut -down, whereas in a systemwhere both lines are insulated a single deadearth Would not immediately amount to a" dead short."

200 V.

(a) (b)Fig. I. Diagrams illustriing earthing problems.

By " MICRON "

to which it is connected, as in Fig. 2 (b),and. so give an entirely false indication-assuming it is sensitive enough to give anyreading at all.

It is a straightforward example of potentialdivision.' Thus :

Voltage from + Side to Earth=P.D. across 4 megohms=4/10, or 0.4 of 250 V. = 500 V.

Voltage from - Side to Earth-6/1o, or o.6 of 25o V. =150 V.

OT -= 250 V. - I00 V. =450 V.Consider, next, the slightly more com-

plicated network of Fig. 3 (a). With the resist-ance values shown, what is the potential ofthe point P to earth ? As before, the 4 and 6megohms might denote the insulation resist-ance of each side.

The four resistances form a WheatstoneBridge,Fig. 3 (b). In one arm we have : 1:13-5,000 hms, PO =4,000 ohms; in the oppositearm : MQ =4 million ohms, QR =6 millionohms, with point Q tied to earth, potential.

If a voltmeter or other resistance (making afifth) were connected as a " diagonal "across points PQ-or from P to earth-acouple o f simultaneous equations

would have to besolved to find thecurrent in this resist-ance, and hence thep.d. As it is, thingsare simple. Thus :

From the + main :Volts dropped

across MQ = 0.4 x25o v.

=100 v. as before.Volts dropped

across LP = 1:5 ;250 V.

=50 V.Point P is 5o v. negative with ,respect to

the + line, and point Q is ioo v. negative.Hence point P is 5o v. less negative than pointQ, or is therefore at +50 v. (5o v. positive)with respect to Q and earth.

The same results would be got by con-sidering the negative line and resistanceslQ and OP.

" Capacitance " Potentials to EarthIn Fig. 4 (a) is shown again our 25o v. D.C.

system, supposed to be perfectly insulated on+ and sides.

Some may find it a little difficult to answerthe question : What is the potential of eachline " to earth," where we have no leakageresistances ? In other words : Would avoltmeter register any-thing if connected

3 -Wire Balancers

250 V.

soot.

2501

To get a clear perspective of why earthingis essential as a safety precaution-and alsoto halve the strain on the insulation of trans-formers, etc.,-consider a transformer secon-dary, Fig. 1 (b), delivering a fairly dangerouspressure, say 500 v. across lines. By earthingthe centre -point of the secondary, the maxi-mum r.m.s. potential with respect to gioundwill be limited to 25o v., which is the highestpressure allowed in domestic installations.

The three -wire D.C. system, Fig. r (c),reduces to the same thing, except that a neutralconductor must be provided right back to thebalancer-there must be no possibility ofbreaking the neutral conductor by fuse links,etc., since the voltages on each side wouldthen be entirely independent of the balancer,i.e., dependent only upon the loads on thetwo sides.

Some Basic PrinciplesAs a useful introduction to insulation

problems in general, let us consider one or twotheoretical examples.

In Fig. 2 (a), two resistances of 4 and 6megohms, respectively, are shown connectedacross a 25o v. two -wire system, with mid -connection earthed. This is an exact repre-sentation of the " leakage resistances " toearth from each line.

The voltage to earth from + and - sidescould be accurately measured by an electro-static voltmeter which takes no current. Anyother type of instrument would shunt arelatively low resistance in parallel with themuch higher leakage resistance on the side

(c)

between a line andearth ? From a safetypoint of view, would a

shock " be receivedon touching either line'_?

A moving -coil or amoving -iron voltmeterwould ',show absolutelynothing-and the sameapplies to every type ofinstrument which hasan internal conductingcircuit. An electrostatictype would register thestatic " charge " in thecapacitances C, and C,(intended to include the

250 v.

internal capacitances in generators, etc.).Each line forms one plate of a " condenser,"

with the earth as the opposite plate, and theinsulation as " dielectric." C, and C, arein series across the line, and are thereforecharged to potentials :

Ca of 25o v.,Ci ± C2

and, CI of 25o V.CI+ C2

Thus, if C, -C,, the potential -differenceof each line " to earth " will be 125 v. Butthe "earth " is 125 v. negative in relationto the + main, and 525 v. positive to theside, which answers the question why thetotal potential -difference must be 25o v.,and not 250- ( -250).

If C, and C, had different values, thepotentials would be calculated as above,remembering that the larger capacitance willbe changed to the lower voltage, i.e., P.D.across C, -C2/(C, + C2) ; P.D. across C,=

+C,).The effect of shunting a resistance R

across one side is shown in Fig. 4 (b). This'resistance might be leakage, a moving -coil ormoving -iron voltmeter, or the " resistance "of a person standing on earth and touchingone main !

Condenser C, will become charged to thefull 25o v., or the p.d. between the oppositemain and ground will be raised from 125 v.to 25o v. Depending upon the value of R,a voltmeter connected between the negativeand earth would show some value of steadyvoltage -25o v. if R was comparatively low,or no reading at all if the resistance was largeenough to pass insufficient current to movethe pointer.

During the minute interval when C, isreceiving extra charge to raise the p.d. acrossits plates from 125 v. to 25o v., a currentwill be flowing in R ; if C, and C, are large,a " shock " would certainly be felt. But assoon as the potential has attained 250 v.,the back e.m.f. in C, will be equal andopposite to the line voltage ; chargingcurrent will cease, and there will be nopotential -difference across R or CI.

Thus, the " earth " would be " charged "to the same potential as the + line, so puttingthat line at ground electrostatic potential.But, of course, in an actual D.C. systemthere will always be some leakage resistancefrom each side, more or less as in Fig. 2 (a),hence it is not so helpful to look at thingshere from an electrostatic point of view.

A.C. SuppliesIrrespective of leakage, the capacitances

1

/00 V.

150 V.

4

10,

4titre

Ain

(b) (c)Fig. 2.-Potential-division " to earth" across leakage resistances, (a).In (b) and (c) is illustrated the effect of trying to measure thesepotentials with a voltmeter of comparatively low resistance R.

Mn

(a)

February, 1948 NEWNES PRACTICAL MECHANICS ' 157

C, and C, will act very differently when thesupply is alternating.

As before, we have virtually two condensersin series across the line, ,with the middleconnection earthed, and the alternating p.d.scan be found by the same rules as in theD.C. case. Only they are no longer " electro-static " potentials. A capacitance behavesmore like a " resistance " to A.C.-or, moreprecisely, a reactance of x 2.-rfC ohms. Ittakes a definite charging -current of constantran.s. value. True, this current is quarterof a cycle leading on the line voltage, butnevertheless flows over complete cycles.

Thus, independent of any leakageresistances, we now have a definite A.G.

path " with part of the line alternatingp.d. across C, and C7, acting as a potential -divider.

Of course, we must not forget thatelectrostatic charges can be extremelydangerous. There are no e.h.t. D.C. systems,but consider an II kV. A.C. feeder of suchlength that the capacitances are considerable.If C, =C2, each will be charged to a maximumpotential equal to half the peak voltageacross lines, i.e., k x 11,000 v. x 1.4=7,700 v.If the supply had been switched off at thisinstant of peak voltage, the lines will remain" charged " at 7,700 v. to earth, and must bedischarged before any work is attempted.The large internal capacitances of machinesand transformers have been the cause offatal accidents through failure to realise suchfacts.

As regards " earthing " the neutral inthree-phase star -connected systems, a numberof somewhat involved considerations enterfrom the standpoint of protection, fault -isolation, harmonic currents or voltages, etc.It is hoped to discuss some of these in futurearticles. For present purposes it is sufficientto know that the voltage " across lines " isv3 =1.732 times that from each line toneutral-or 73.2 per cent. greater than thephase -voltage. Hence, two alternativepressures are available for domestic andother consumers, whilst by solidly earthingthe neutral the maximum potential to groundis limited to the phase -voltage.

A great deal more might be written onthese questions, but possibly the foregoingexposition of a few principles will help.

Racing Characteristics of MotorsThe reason why D.C. motors will, under

certain conditions, " race " at dangerousspeeds is seldom well understood.

A car starter motor I saw tested on thebench the other day is a case in point.Connected to a 12 v. battery, it acceleratedrapidly to a speed which developed into a" roar." It was obvious the machine hadnever been designed to run at such a speed,and a breakdown would inevitably haveresulted if left to accelerate.

For a motor of this type wouldaccelerate until something gave way-usually the commutator segments are " thrownout " by centrifugal forces, which is quiteenough to start with !

Of course, many readers will know that astarter motor is a series machine. The fieldwindings are connected in series with thearmature, and, when this is so, the motorwill run at normal speed only when coupledto its mechanical load. If started whenuncoupled from the load-or with too lighta load-the field will become very weak, withthe result indicated.

But it should not be forgotten that shuntmotors, too, can race. I have seen quite afew doing so, with sad results. Normally, ashunt motor will not run at excessive speedwhen disconnected from its load. The fieldis energised directly across the supply, andas long as we get normal field the speed willbe about the same on no-load and full-load-there is a drop of a few per cent. (depending

0

(a) ( b)

Fig. 3.-Analysing a slightly more complicatednetwork. What is the potential of point P

" to earth" ?

on the size of motor) when the load comes on.Shunt-wound machines are not employed

for car -starting, or for any other heavyduties such as traction, because the seriestype can exert extremely large startingtorques-at least, that one reason will doto get on with. On the other hand, a motorwhose speed is likely to undergo violentfluctuations with load changes would berather hopeless, say, for a machine -shop drivewhere no large starting torque is necessary.

If, however, when on light load, theshunt -field connection is broken at some point,a shunt motor will race much the same as aseries motor running on no-load. If there isany appreciable load on the shaft the shuntmotor will not accelerate dangerously, sincethe excessive current will blow the fuses.

It may not be very clear how any motorcan run even at normal speed when thewinding responsible for providing a fieldis disconnected ? Actually there will beresidual magnetism-weak though it is-toprovide enough torque for acceleration atlight load, whilst it is possible for the armaturecurrent to reinforce this field.

+ : #

'Ti,

250 v. f- -+E

,C' 2

T/

250 v

.C2

(a) (b)Fig. 4.-" Capacitance Potentials" to earthassuming (a), a perfectly insulated D.C. system.In (b), a moving -coil voltmeter of resistance Rwould discharge " condenser " Cr, throwing the

full 250 v. across C2.

Speed/Flux Relationship°What is difficult to understand is why

the speed of a motor should increase whenthe flux is made weaker.

Another catch question involving the sameprinciples is this: Would a motor run faster,or slower, if more " turns " were put on thearmature ?

The answer to all, such problems is simpleonce a few fundamental facts are understood. First, at a given speed a machine takes adefinite amount of power from the supply.Thus, if on no-load, the power will be justsufficient to make up all the losses : friction,windage, magnetic core losses, etc. It isrunning at a steady speed because of thisstate of balance where' power suppliedtotal power losses.

If for any reason more power is supplied, itwill now be in excess of the amount requiredto balance losses at the " given speed," sothe armature accelerates to some higherspeed where, once again, increased power

supplied =increased total losses. It willcontinue accelerating until this fundamental" equation " is exactly true, after which thespeed will again be steady at some highervalue.

After all, these facts are obvious, oncestated. They are necessarily true of allmachines, not only electric motors.

But in the motor we have another" governing " device-an electrical one, whichcauses the machine to regulate its powerrequirements automatically to suit the loadconditions. This is the counter e.m.f. orback e.m.f. generated in, the armature coils.

The important thing to realise regarding a" back e.m.f." is that it annuls part of theapplied voltage, in so far as a portion of thelatter (equal to the back e.m.f.) will not beavailable for overcoming resistance-or forgiving rise to a current. A numericalillustration will make this clear. -

If we had a supply at 200 v., and if thearmature of a motor developed a countere.m.f. of 199 v., the only effective voltageproducing a current in the circuit is 200 V.-199 V.= I.0 v. If the resistance of thearmature is 0.04 ohm, the current will ber.o v. o.o4 -25 amperes-a fairly large" amperage," since, although we have' onlyi.o v. available for overcoming resistance,that resistance is only four -hundredths ofan ohm.

All this, of course, boils down to the basicequation for a circuit having a back e.m.f. :

Current I=V eR-

where V -the supply voltagee =the counter e.m.f.R =the circuit resistance in ohms.

If we denote the resultant voltage (V -e)by some symbol, such as v, we have simply :

I -viRThus v is the difference of two e.m.f.s

that will normally be almost equal, e.g.,zoo v., and 199 v. as above. Also, becauseof the low " R," a small change in thisdifference, i.e., a small change in the backe.m.f. can give rise to a relatively large changein the current.

For example : If the counter e.m.f. droppedfrom 199 v. to 198 v. due to an extra " pull "on the shaft, the current will rise from25 a. to 5o a., and the power taken will thusbe increased too per cent. Observe that theback e.m.f.-and the speed-has dropped byonly I v. in 199 v.-a little more than 0.5per cent. It explains why a shunt-woundmotor (having a constant field) is practicallya constant speed machine.

What will happen if we weaken the field ?The immediate effect will be a reduction in" e "-everything else remaining constant inthe above equation. The armature at oncetakes more current and power from thesupply, much in excess of that required forthe speed at which it is at present running.In fact, the increase of power will accelerateit to a higher speed ; e will increase, thecurrent " I " will fall, until Volts x Amperes(VI-Power) is just sufficient to maintain asteady speed at some higher value than beforethe field was weakened.

It is not quite correct to say " the speedwill increase until the back e.m.f. is the sameas before." No machine can run at a higherspeed, taking the same power. As seen, theback e.m.f. will always be of about the samemagnitude as the applied voltage. In thiscase, if it was 199 v. before weakening the field,the motor will accelerate so as to generate,say, 198.7 v. ; with the reduced flux, itcannot become 199 v., exactly the same as atthe lOwer speed.

From this there should be no diffi-culty in explaining what the armature is" trying to do " when it is racing under veryweak field conditions. It should also be cleat

- that putting more turns of wire on an


armature will reduce the speed, since a givenback e.m.f. can be generated at a lower speedthan before.

A " Power " ProblemWhat value of resistance should be put in

series to halve the power in a resistance of20 Ohms ?

This question cropped up in connectionwith a heater, but I am not going to giveany kW. or voltage figures, because thecorrect answer is not at all dependent uponthem. You are given only the resistance(20 ohms), and you must do the rest.

Quite easy if approached the right way,though I have known a page of quadraticexpressions used to arrive at a solution-fromlack of a little clear thinking about " PR."

One or two points should be noted. First,it is the power, not the current, which is tobe .halved. Secondly, we want to halve thepower in the zo ohms-not the total powertaken from the supply. Therefore, theanswer is not " another 20 ohms in series."Evidehtly that would halve the current andhalve the total power-at a constant supplyvoltage ; the power in the 20 ohms wouldthen be reduced to one -quarter.

To halve the power in a given resistance,in what ratio should the current be reduced ?What extra resistance must be added to give

- this current reduction ? Reasoned along theselines the answer is almost self-evident. Itis about 8 ohms extra resistance in series,making a total of 28 ohms.

What would be the total power saving asa result of using such an arrangement ? Thepower has been reduced 5o per cent. in onepart of the circuit, but the series resistancewill dissipate some-the total reduction inthe power from the supply will not be asmuch as 5o per cent. Roughly, it will bealmost exactly 3o per cent.

Anyhow, see if you can spot the easyway of arriving at the answers.

Rectifier InstrumentsFrom time to time I have had numerous

queries from students and others regardingthe " form factorerror " to which A.C.instruments incorporating rectifiers are subject.

A point of some difficulty is to understandthat these are not r.m.s. instruments proper.The scales are calibrated to show r.m.s.values, it is true, but the figures must notbe taken as " fixed " and correct for all sortsof alternating currents ; in fact, they arecorrect only for a sine -wave.

Any meter embodying a rectifier is an" average current " instrument. The alternat-ing current is rectified, becomes " pulsatingD.C.," whilst the moving -coil instrument givesdeflections proportional to the " average ' or" mean " value of this varying D.C. Upona sine -wave assumption, the instrument isthen scaled -off to read what the r.m.s. valuesshould be with an ideal waveform.

If rectified as described (i.e., full -waverectification), the average current will beabout 0.637 of its maximum value at the peakof a pulse, whilst the r.m.s. value will be0.707 of the maximum as for a sine alternatingwave. Thus the r.m.s. value is 0.707/0.637= 1. r r times, or t t per cent. greateir than themean value-still upon a sine -wave hypothesis.

The important thing to realise is that ther.m.s, calibrations are strictly correct only forone particular waveform. For any otherwave -shape, the mean current will not be0.637 of the maximum, neither will ther.m.s. value be 0.707. The form factorwillthus be some figure other than r. r r. It allboils down to saying the " ideal " scale -calibrations will not be correct.

An r.m.s. instrument, proper, reads thetrue root -mean -square value, no matterwhat the waveform. The reading depends,for instance, upon the heating effect of thecurrent to be measured. The heat developed

in a wire is proportional to the mean power-not the mean current-and " r.m.s. value "simply signifies the effective current whichis the equivalent of this average power.

Thus, the heating effect will depend uponthe wave -shape, but the instrument indicationwill vary accordingly, still representing thetrue effective current value. There can beno " form -factor error," because the averagevalue of a rectified current simply does notenter into the matter.

Power -factor CorrectionIn simple terms, why is it necessary to

" correct " a lagging power -factor, if, asstated, a "wattless current " does nothingwhatever in a network ?

This question can most profitably bediscussed by taking a concrete example.Suppose you had a load of induction motorsor electromagnets taking a total true powerof 1 kW., but at a power -factor let us say aslow as 0.5-probably 0.7 or o.8 would benearer the mark under full -load conditions.

What size of transformer would you orderfrom the manufacturers ? No doubt, anymanufacturer of standing would want toknow more about your " load " beforesupplying a transformer, but if you purchasedone advertised secondhand as being " r.okilowatt," the meaning of power -factor wouldsoon become evident !

For although there is a " wattless " currentcomponent in the circuit, the total currentthe windings have to carry would be thatcorresponding to 2 kVA., not t kW., andthe wire used must be thick enough to carrythe total current-" wattful," and " wattless."

Remembering that power -factor is thecosine of the phase -angle, a p.f. of o.5 meansa current lagging 6o degs. on the voltage.Suppose the total current is IooA., lagging6o degrees.

The wattful (in -phase) component is

tooA X cos 6o° -50A. The wattless com-ponent is tooA x sin 60°=86.6A. The latter" does nothing." Nevertheless, the transformersecondary must carry tooA., not 5oA.-thecurrent equivalent of the " true power."

In fact, if the power -factor was correctedto unity (cos s6 = 1.0), 50A. would be theonly current. The heat generated in wiresvaries as " IzR," so if windings designed tocarry 5oA. are loaded with tooA., there isgoing to be a pretty serious temperaturerise !

The Supply AuthorityApply the argument to all the transformers,

cables and generating plant the supplyauthority has to provide, and it will be clearwhy he is bound to impose drastic penaltiesto consumers whose p.f. is notoriously poor-charges of such magnitude as will render" correction " an economic necessity.

The " size " (kVA. rating) of plant rightback to the central station is partly determinedby the total current to be carried, whilst that,as seen, varies in an inverse proportion tothe power -factor.

What are the things responsible for poorpower -factors ? Actually, anything thattakes an A.C. magnetising-current-electro-magnets, transformers, induction motors,etc. This current is purely lagging, by90° on the supply voltage, and while usuallysmall compared with the normal full -loadcurrent of a particular piece of equipment,a large number of such " pieces " coupledto the supply network, many of which maybe on light loads for appreciable interval,will load the system heavily with reactivevolt-amperes.

If p.f. was looked at from a practicalangle instead of merely remembering it issomething given by " cos q," it would helpas an introduction to aspects of supplyeconomics generally.

The New Twin-engined "Aerocar"

Many new aircraft not previously seen in public were on view at the flying display and exhibitionorganised by the Society of British Aircraft Constructors, at Radlett, recently. It was the biggestshow of its kind held in this country, and visitors from all parts of the world viewed the aircrafton show, including the machine illustrated, the Portsmouth Aviation Company's new " Aerocar,"

a six -seater, powered by two Cirrus major engines.

February, 19 48 NEWNES PRACTICAL. MECHANICS 159

The Elements of Mechanicsand Mechanisms -4

The Second Law of

By F. 1. CAMM(All Rights Reserved.)

Motion Falling Bodies : Forces Acting in Opposite DirectionsIF a ball is struck with a cricket bat so that it

travels with a velocity of 5ft. a second,and whilst the ball is in motion it is

struck with a second bat with a similar force,it will have a velocity of 'oft. per second,thus the second force acting on the body inmotion has produced a velocity the same inmagnitude and direction as if the force hadacted on the body at rest.

Now take the case of a boat on a runningstream or river. Assume that in still water anoarsman can propel a boat at a speed of five

' miles an hour. Assume also that the sameoarsman using the same force propels hisboat on a stream which runs at the rate offive miles an hour. It therefore follows that,when rowing in the direction in which thecurrent is flowing, his muscular force, plusthe current of the stream will produce aspeed of five plus five equals so miles anhour. This is called the resultant velocity.If he rode against the stream his actual speedin relation to the rives bank would be nil.If the speed of the stream were two miles anhour, the speed of the boat in relation to thebank would be three miles an hour upstream.

The velocity of a falling body provides afurther example of the application of thesecond law of motion. Assume that the forceof gravity acts for one second upon a body.During this time that body will fall a distance of16ft. and will acquire a velocity of 3aft. persecond. If gravity then ceased to act the bodywould fall 32ft. during each succeeding second.We all know that gravity does not cease butcontinues to act irrespective of time.

During the second second, therefore, thebody will fall through 32ft. by virtue of thevelocity attained at the end of the first second,and through an additional 16ft. because of thecontinued action of gravity, thus making atotal distance traversed during the secondsecond of 48ft. At the end of the second secondthe falling body will have a velocity of 64ft.per second, which would carry it through64ft. in the third second. But the force ofgravity urges the body through 16ft. in thisthird second just as in the first, causing thetotal distance traversed in the third second tobe 64+ 16 =8oft. It is, therefore, clear that aforce acting on a body in motion will produceits full effects apart from any motion the bodymay already have. In other words it willproduce exactly the same effect as if it actedon the body at rest. We may summarise thisin the form of a rule :

The resultant velocity of a body urgedonwards by more than one force in the samedirection will be equal to the sum of thevelocity that the forces would produce if theywere to act separately on the body at rest.Forces Acting in Opposite Directions

The vertical velocity of a falling bodyincreases until the upward resistance of theair on its surface is equal to its weight. Thevertical acceleration is then zero and a maxi-mum velocity has been reached. Thisvelocity is called the terminal velocity, and itdepends on the weight of the body in relationto its windage. It is obviously affected by theshape of the body, streamline form giving thehighest terminal velocity for any given weightand body. The heavier the body the higherdoes its terminal velocity tend to be.

Terminal velocities can be determined with

reasonable accuracy only from special tests.For heavy bombs they are of the order of70o to i,000ft. per second. Similarly, therate of acceleration during ascent can befound with certainty only by experiment, butthe following analysis gives a reasonableapproximation to actual conditions if theterminal velocity is known. It assumes thatair resistance is proportional to the squareof the relative Velocity, and it is known thatfor bodies that approximate to streamlineshape this is very approximately true.

The downward acceleration of a falling bodyis equal to that due to gravity minus that dueto air resistance, or : g -ku-, where k is aconstant to the body and u is its downwardvelocity. If the terminal velocity is U,

g -ku"--o by definition. Hence k=U" and inu"general acceleration d° = g (1 --IP).

duThis gives -u'iU2 = g dt.

and by integrationU i+u/U-- log,2 I - U/u

whence u-Uexp (2gt/U)- zexp (zgt/U)+I

Here exp (2gt!U) means e2gt'U where eis the base of Napierian logarithms. Inhandling numerical values it is convenientto use the identity et -antilogio 0.4343 x.

If s is the vertical distance of descentfrom an instant at which the vertical velocityis zero,ds- -1.1, and integrating (2) is found thatdt

(I)

(2)

U 2 exp .(2gt!U)s =U [t -log,(3)exp (2gt/U)+Equations (2), and (3) may be used to deter-mine velocity and distance below the startingpoint after any time t. The time taken toattain any velocity u is determinable from (i).The time taken to fall through any distances may be determined from (3) by repeatedtrial.

For example, if U -700 f.s. and s = zo,000ft,insertion of numerical values (includingg=32.2 f.s.s.) in (3) leads to

700 2 exp 0.110.9)10,000 =700 [ t -log,32.2 exp (t/i0.9) +

, 2 exp (00.9)Or 14.29 -21.75 tog, q..)exp (t/to.9)-F I

In the case of a free fall without air resist-ance, the time taken to fall through a distances is

2S s If S =-10,000, this is 17.63 sec.g 4.01

The actual time will be longer than this.If the, velocity were equal to 700 f.s.

continuously, the time taken would beto,000- - -14.3 sec. The actual time will be

7oolonger than this.

As a first trial some value of t greater than17.3 should be used, say 1=25. With thisthe value of the right-hand side of ,4) is

25 -21.75 log. 1.818=13 instead of 14.29.It is found that t=28 leads to 14.55, t='27

leads to 14.05 and t =27.8 leads to 14.35.

Hence the value t=27.8 may be acceptedas being sufficiently accurate.

The vertical velocity on reaching theground is determined by inserting this valueof t in ,(2), where

2gt/U =2 < 32.2 X 27.8/700=2.56Then exp 2.56=12.88 and so

12.88 -1u-7oo 12.88+1-600

Horizontal VelocityThe variation in horizontal velocity during

the fall is less easy to estimate. The initialhorizontal velocity is that of the aeroplaneat the moment of release and the horizontalair resistance may be taken as proportional tothe square of the horizontal velocity. Theexact value of the resistance for any particularvelocity can be determined only from actualtest on the particular bomb, but it may beassumed to be at least four times'for the samevelocity in the direction on the axis of thebomb. On this basis the horizontal retarda-tion (i.e., perpendicular to the axis of thebomb) due to air resistance at a horizontalspeed v is equal to 4uv: g. Where U is (asbefore) the terminals velocity in a free fall.

Starting from an initial velocity V, thehorizontal acceleration at any time t

dr v"g

and by integration this givesg t+K

where K is the arbitrary constant of integra-

v =V when t=o, K =V

Vand so v4g1-1-4gVt

tf-' " V UzTaking the previous examples in, conjunct -

lion with initial horizontal velocity V=250m.p.h. =367 f.s., the horizontal velocity onreaching the ground, i.e., after time t=27.8secs., is, by (5)

367 367V -e+4 X 367

X 27. 8-36.9The striking velocity is the resultant of

600 f.s. vertically and 99.5 f.s. horizontally,i.e.,

1/(6002+ 99.5') - 608 f.s.The horizontal travel of the bomb between

release and impact with the ground is deter-

mined by writing v=-.: in (5) and integrating.

This gives' , V

s 4gU log,U(1 I 4g'

(5)

(6)

Using the same numerical values this givesfor the horizontal travel on reaching theground

4

00log, (14 4x 32.2 X 367

X 27.8)72.

7002

=4,970 ft.(To' be coh tittered.)


Makin a Pin -hole CameraConstructional Details of an Easily -made Instrument

By E. S. BROWN

APIN -HOLE camera can be veryinstructive and interesting and, pro-vided that its limitations are realised,

quite good photographs can be taken withthis simple camera. Of course, one cannotexpect the results of a camera costing manypounds-indeed, it would be foolish to do so-but with little practice quite creditable andpleasing results can be obtained.

The pin -hole camera is,, of course, novelin that it functions without any lens ; theimage being cast on the sensitised platesurface by a small pin -hole. This strangeoptical feature is often duplicated in natureby sunlight filtering through the foliage oftrees, and projecting a true image of thesun wherever a break in the foliage allows aminute shaft of sunlight to penetrate andstrike an object.

The camera that is described in thisarticle can be yery easily made from the mostelementary materials, and provides photo-graphy in its most simple and inexpensive form.

Fig. i.-An " exploded " view of the pin -hole camera.

Constructional DetailsTo construct the camera, two pieces of

gin. by 6in. by fin. and two pieces of gin.by 5f in. by tin. smooth wood are required.These are rebated fin. along both edges, andjoined together with panel pins and glue toform a box gin. long and 6in. square. Thefront of the camera is made from a piece of6in. by 6in. by 4 -in. wood rebated to make adose fit into the sides. It will be noticed thatall the joins in the camera are rebated. Thisensures a practically light -proof form ofconstruction. A hole fin. diameter is nextdrilled through the exact centre of the front,which is then fixed into position with glue andpanel pins. (Fig. z.)

The " lens " of the camera is made from apill -box or similar article, preferably of themetal variety, complete with lid. A small holeis made in the dead centre, of the pill -boxwith the aid of a normal -sized pin. The sizeof the hole determines the ultimate speed ofthe camera, and the clarity of the photographstaken. Unfortunately, in the pin -hole cameraone cannot have both. A small aperture isconducive to clear pictorial detail, but if theaperture is too small then the time of exposureis unduly protracted. Therefore, the .resultmust be a compromise, and a normal -sizedpin -hole will be found suitable for mos:purposes.

The bottom portion of the pill -box is nowplaced on the front of the camera so that thepin -hole in same is exactly centralto the hole drilled in the camerafront. With a washer of, thickpaper interposed between thepill -box and camera front, fastenthe pill -box into position with twosmall screws. Needless to say, itis of the utmost importance tomake sure that a light -tight fitis made, and the camera shouldbe held up to the light andthoroughly checked for any light -leakage, not only from the pin-hole assembly, but also from thevarious joins at the sides and frontend of the camera. If any leakageis detected it should be paintedwith a mixture of glue andlampblack. Sufficient lampblackshould be added' to make theglue opaque. Slight difficulty may

be eiperienced in renderingthe glue and lampblackmiscible, due to the oilynature of the latter. If,however, the glue is main-tained at a fairly hightemperature it will be foundthat by adding the lampblackin small quantities, and wells t i r r i n g, the recalcitrantproperties of the lampblackwill be overcome.

Plate CarrierThe back of the camera is

made from a piece of 6in.by 6in. by in. wood, rebatedfor a distance of fin. fromthe ,edges. A plate , carrieris constructed of tin, asillustrated, and is screwed

8 exactly central to the back ofthe camera. The overalldimensions of the plate carrierare 4Iin. by 3Iin. The

6'-.AV Eye Fastene.

Rebate

PlateCarrier

Runners

h'ed Plush Clued /1)Rebate

11111111111111Fiieing Screws

Fig. 2.-Back of camera and detail of plate -holder.

Plate Carrier

The completecamera. (Note

the position of theview -finder).

runners are f in. in width, and provide a s /z6in.clearance to accommodate the plate. (Fig. 2.)

The carrier should allow the plate to slidefairly easily into position, but at the same timethe plate must be held securely in place. Ifthe plate is not satisfactorily secured, therunners should be slightly bent inwards toincrease the tension on the plate.

A strip of red plush is now glued on to therebate to ensure a light -tight join when theback is closed. The hinge is made by glueinga piece of American cloth or similar material:on to the back and one side of the camera.On the opposite side a hook and eye fasteneris fixed. Care should be taken to see that whenthe back is closed slight tension is imposedon the fastener. This ensures a perfect lightseal.

The inside of the camera and the pin -holeassembly must now be painted with a mattblack finish. This finish or paint can beobtained at most photographic stores. Aglossy paint should not in any circumstancesbe used, as the reflection from its surface willalmost certainly cause " fogging " of the

.,negative upon exposure.The exterior finish of the camera can be

left to the readers' choice. American clothor leatherette glued into place gives a verypleasing appearance, and, moreover, has themerit of being easily cleaned. Of course, ifone decides to cover the camera in one ofthese materials the hook and eye fastenermust not be fixed until after the camera iscovered.

The camera illustrated was covered inleather removed from a very old damagedbox camera. Although the job was difficult,the results were very satisfactory.

View FinderThere, finally, remains the view -finder to

make and fix into the correct position. This ismade from a piece of fairly heavy gauge wire,41in. in length by 3f in. in width. This issoldered centrally to a piece of tinplate 6in.long by sin. wide. The view -finder unit isthen secured to the extreme front end of thecamera with three small screws, and thecamera is then completed.

As before stated, the camera has certainlimitations to its use. It is not possible to takeinstantaneous exposures, which, of course,implies that the subject must be immobile,The time of exposure depends, of course.upon the rapidity of the plate used, and the

February, 1948

quality and degree of light at the time of taking.This usually varies between three seconds forbrilliant sunshine, and upwards of 20 to 3oseconds for varying conditions.

When taking landscape views a bright,although not necessarily sunlight, day shouldbe chosen, and should the subject includetrees and foliage in the foteground, a calmday is necessary, otherwise the movementof the trees will blur and spoil the photograph.

LoadingTo load the camera first see that the cap

is in position over the pin -hole attachment.


The plate required is 41in. by 31in., or quarterplate, and it should be fairly rapid. It shouldbe loaded in a dark room by sliding the platein the carrier with the emulsified surfaceuppermost. With some plates, notably thePanchromatic type, it is not permissable toload with the aid of a normal dark -room lamp.In this case, the emulsified side of the plate canbe detected by gently stroking the finger acrossboth surfaces of the plate. The sensitizedsurface can be found by its matt textureas opposed to the smooth feel of glass.

Before detection by this means it is advisableto wash the hands, otherwise there is the risk

161

that the natural oils from the skin will bedeposited on the sensitised plate surface, andso preyent the full development of thoseaffected parts. When the plate is in positionsecurely fasten the back of the camera, and itis then ready for use.

When taking a photograph choose a daywhen the light is intensive and strong. Restthe camera on a firm basis, and sight the objectthrough the view -finder. Steady the camerawith the left hand, and with the right removethe pin -hole cap for the necessary duration ofexposure. When the exposure is completedreplace the cap as quickly as possible.

ObservationsFurther Interesting Scientific Facts About Everyday Topics

By Prof. A. M. LOW

(Continued from page 122, January issue.)

ReactionEVERYONE talks nowadays of reaction,

but they mean, as a rule, that they aretired after the strain of war. Reaction

has a technical meaning too. It is equal toaction, as one of the first laws of mechanicstells every student.

If I push you against a wall, my feet orbody push equally hard in the opposite direc-tion. A bullet flies from a gun but thegun jumps too ; being heavier it jumps lessfar.

My car has just been rebored and everytime I cautiously accelerate in neutral the car,shivers because it is trying to turn round theengine just as much as the engine is turninground in the car.

Relative speeds offer some comparableproblems. Bullets fired from trains at theengine driver can hit him because their totalspeed is that of the bullet plus the train,relative to the earth. Fired from the track,they merely run beside the driver if the speedof bullet and train are (most improbably)equal.

When you step on to a moving platformor stairway, walk quickly so that your bodyand the track travel together. If you walkat the rate of the moving platform and standstill when reaching it, there will be no shock.This avoids all chance of " after -dinner."accusations !

SecretsT CAN scarcely remember one occasion1 when I have ever approved of secrecy.In the first place it is nearly impossible ; andsecrets nearly always do harm in the end.

That is one reason why science is not verypopular. Until quite recently science wasrather frowned upon in England, and waslooked upon to some extent as the prerogativeof poor people while the wealthy devoted theirtime to the glories of Plato, Socrates. andLouis XIV. Or were supposed to do so.

All this brushes aside the brutal truth thatunless dead languages and old thoughts canbe reborn as something new or original theyare next door to worthless. The medicalprofession have been sinners in this respect.Everyone knows that many diseases havegrown due to the secrecy surrounding theironset. I understand that both cancer andT.B. can often be cured or rendered innoc-uous when taken in time. These things arenot matters for whisperings.

Nor do I like the extensive use of Latin,or rather Dog Latin, terminology for I think

it gives the partly educated an unfair advan-tage over those who are too easily impressed.I had the honour to learn chemistry from thegreat Professor Armstrong, and I recollectthat he would never allow us to speak ofsulphuric acid until we knew what we meant." Call it firewater," he would say, " in themeantime."

Patent MedicinesLOOK at the number of patent medicines

which are sneered at because they arepatents, although this trouble has now beenremedied in most casts by the new PatentLaws which do not permit a combination ofa few chemicals to result in worthwhile pro-tection ! One hears people say " How absurdto charge 5s. when the materials are worth afarthing." " Not at all," I reply ; " they arewell combined, conveniently manufacturedand they do their job."

So let us sweep away this idea that sciencebelongs only to a few queer men with bigblack hats and bushy hair. The housewifeusing soda for cooking, or bicarbonate of sodain bread, may be making a complicated ex-periment. As well treat this a secret as theatom bomb. In short, it is impoSsible to keepit dark.

If I mix a little acid and a little bicarbon-ate of soda into a pudding, carbon dioxide isevolved. Just the same gas that so manyfire extinguishers produce. A gas which isinert, can be used for preserving apples, andwhich comes out of our lungs every time webreathe. The chemical actions which can be expressed in complicated symbols really needno glorification.

If hydrochloric acid is used with chalk asa " riser " the pudding would rise most excel-lently. Some of the carbon combines withsome of the oxygen to produce carbon dioxide,some of the calcium in the chalk combineswith some of the chlorine in the hydrochloricacid and a little water in various stages ofcomposition is also released. The real pointis that chlorine, a deadly poison, is quiteharmless when combined with something itclings on to out of the chalk.

There are many similar examples. Thinkof the hydrogen from the gas jet which com-bines with some of the oxygen in the air, boilsyour kettle, forms steam in doing so longbefore the kettle boils, and then probablycondenses on the bottom of the kettle beforethe rate of heat transfer becomes great enoughto turn the water drops outside the kettleinto steam. All very scientific indeed.

Flowers Can Think !THERE is no need to look at pictures with

ones' head on one side although it mightbe logical not to look at them with the verycentre of the eyeball. Let me explain. Themillions of sensitive points which make upthe retina at the back of the eye are of differentkinds. Some seem so shaped as to be 'verysensitive to light, while others appreciatecolour.

You will have noticed that looking at aclock in a dimly lit room it is better to looka few inches to one side for this brings thelight-sensitive part of the eye into betterplay and the time is more easily seen. Colour,I imagine, should be looked at straightlybecause it is in the middle of .the eye that themajority of colour cells are found.

But to return to nature ; not literally.We rely upon artificial aids for most pleasures,and this is natural in an era when we try tosubdue the body that our minds may improve.

Flowers turn to the sun, some catch flies,others shrivel up' when touched. They aresentient. How can we be sure that they donot think and that, in fact, some are not evil ?Not evil because they may be poisonous,which doubtless has a vital purpose, butnasty in their outlook. Flowers may be, Ithink, on an infinitesimally smaller scale,living, thinking, and instinctive parts of life.Do you experience no feeling of diffidencewhen you cut down a "tree ?

What Are the ConsequencesTHAT depends upon what you have done.

But to be very serious, I have alwayswanted to write a book on conseqtiences andplatitudes. The latter are too terrible, for Ilisten to them all day in railway carriages andin restaurants. Why do people imagine thatone wants to hear their noise any more thanwe would care to notice their smell ?

Consequences are quite different. They atefascinating because of their illimitable range.Might it not be that wars are caused by awoman who loses her . comb (id. combs areis. in London streets nowadays) annoys aman and so on ? Could not a squabble betweenMr. and Mrs. Engine Driver one morning,account for an accident ? Why do some seedsbecome weeds over long periods of rest ;what, in fact, is the result of every thoughtwe make ? For thoughts do make materialthings in time.

"Action 'Stations"IN about the year 1916 I was at a shore

station awaiting the arrival of a submarinefleet which had been signalled in enormousnumbers. Guards turned out, it was " actionstations " and guns were loaded. A fewminutes' hurried investigation showed a smallfly to be stuck across the wires of an indicating,galvanometer. Think of sonic of the con-sequences of things you have done, and youwill realise when you wake up how far youhave travelled. I cannot say I believe whole-heartedly in chance.

162 NEWNES PRACTICAL MECI-1ANICS February, 1948

Notes on OpticalCalculations

A New Method of Working Which Simplifies Optical ProblemsBy D. C. STILL, F.S.M.C.(Hons.)

IT is frequently necessary for the engineeror model constructor to work out a simpleoptical system and, unless he has retained

a very good grasp of his earlier lessons inphysics, he may find the task somewhatdifficult. There are, unfortunately, severalquite different " sign conventions in yogue,and the tiro is often puzzled by the fact thatth sign in the well-known u v (conjugatefoci) formula seems to- vary from text -bookto text -book in the most inconsequent way.

It is the writer's intention therefore, toendeavour to clear the air a bit in regard tothese formulae, and to present a newer methodof working which greatly simplifies, opticalproblems. This necessitates the introductionof a unit little used except by opticians-the dioptre-but readers will find a clearconception of the term most helpful.

Card Screen

Imege In SheepFocus

Lens(t18 0)

Fig. 1.-Simple apparatus for finding the foeWhen the conventional formula: connecting

object and image distances with the focallength of a lens are used, great attention hasto be paid to the direction of the light, anda plus or minus sign given to it according tosome arbitrary convention. Depending onthis convention, the sign in the formula maybe either plus or minus ; hence the confusionamong students transferred from one collegeto another where a different sign conventionis in use. In the method I shall presentlyoutline there are only two things it is necessaryto understand-the dioptric system, and theelementary principles of the behaviour oflight on reflection or refraction. No formulaeare required ; and the sign convention,depending directly upon the type of lens ormirror used, cannot possibly confuse. Allthat is really required in addition to a know-ledge of the rudimentary principles ofrefraction is a logical mind.

The DioptreThe ,dioptre is a unit of vergence (con-

vergence or divergence), and is given by thereciprocal of a focal length or other opticalmeasurement in metres. Thus, a lens whichhas a focal length of 20 cm. will have a dioptricpower of .2 M. -5 dioptres ; if its focallength is 8o cm. it will have a focal length of100 CM./80 CM. =1.25 dioptres.

Similarly, if a mirror has a focal length of8 cm. its dioptric power will be too cm.18 cm ---12.5 dioptres (written 12.5 D.). Incidentally,I would remind readers that the focal lengthof a curved mirror is not to be confused withits radius of curvature ; the radius of curva-ture being always just double the focal length.

The advantages of the dioptric system arevery great. lit the first place, a good idea of

the power of the lens is obtained in manageablefigures. Moreover, the stronger the powerof the lens, the higher its dioptric number.Again, a combination of two or more lensescan easily be calculated simply by adding theirrespective dioptric powers, whereas their focallengths admit of no such simple calculations.Finally, the focal length can always be gotback from the lens by the simple expedientof taking its reciprocal again ; a 2 dioptrelens has a focal length of 1/2 m.=50 cm.,or a lens of 5o cm. focal length has a dioptricpower, of 11.5 m.=---2 D. It is just as simpleas that.' The optician always works in dioptres,which grew out of the focal length systemmany years ago. Of course, if you know thefocal length of a lens accurately in inches,it can still be converted to dioptres quiteeasily. There are 39.37in. in a metre-near

enough 4oin. Divide,therefore, the focallength of your lens ininches into 4o, and youagain find yourself withits dioptric power.

Finding Focal LengthYou may have a

collection of lenses byyou, but have shied offtrying to do anythingwith them because youhave no idea of theirfocal lengths. It is verysimple to find out what

their powers are. Simply set up your lensat one end of a ruler, and focus a distantobject (in practice anything over loft. away)on a piece of card set up behind the lens insuch a manner that it can be slid easily alongthe ruler. The diagram, Fig. I, should makethis clear. Then the distance of the lensfrom the card screen is its focal length.

If you have a lens of very short focal length,or a concave lens, the quickest and mostaccurate way to find its focal length is to takeit along to your optician, who should be ableto tell you within an astonishingly short timeexactly what its dioptric power is. Don't,however, worry him with microscope objec-tives or combinations of thick lenses.

Light From DistantObject

al length of a lens.

Convergent and Divergent LightCertain basic facts about lenses and mirrors

even the youngest student knows well.A convex lens always converges light ; so doesa concave mirror. A concave lens alwaysdiverges light ; so does a convex mirror.So much we all know.

It is not, then, too much to ask us to con-sider any lens or mirror which converges light,or any convergent beam of light, as " plus."

S

("4/3 a 40)Fig. 3.-If the direction of light is reversedsigns of object and image distances will betransposed, but the calculations remain identical.

10' 3Metres--P:30-.-.

Ca) +80

Para//e/ Light From DistantObject

(b)Light Source +SD

Y8..459in

331/3eim-30) (zi-sd)

Fig. 2.-Diagrams showing parallel light,and divergent light rays impinging on a lens.

On the other hand, all lenses or mirrors whichdiverge light, or any divergent beam of light,are to be considered minus." In the specialcase of light coming from a source it is alwaystaken as minus, because it diverges, spreadingout in all directions. If, therefore, we' have asource of light quite near to diens, we are ineffect using divergent light, and the focus ofthe lens will correspondingly be altered.

Consider, for instance, the exampleillustrated in Fig. 2. In the first sketch(a) we have parallel light impinging on =-8 dioptre lens. As the focal length of thislens is m.,the light will be brought to afocus 12.5 di. from the lens. Now supposeour source is brought to 33 cm. from thelens (Fig. 2b). The light f,rom the source isnow divergent, and the focus of the lens willconsequently be farther away.

But how much farthey away? Well, thelight divergent 33 cm. from the lens has adioptric vergence of -3 dioptres. We have,therefore, light divergent -3D redirected bya lens of? plus 8D. It is not difficult to seewhat the result is going to be. Recall thatyou can add and subtract dioptres-that theyare not difficult to handle like focal lengths.So we have minus 3 plus 8, equal to plus 5dioptres. The reciprocal of +5 gives you theimage distance in metres, so that the lightconverges to a focus on the image side of thelens at a distance of 20 cm. from it.

In case there is any shadow of doubtremaining, look at it like this : A convergenceof 8 acts on a divergence of 3 ; there will thusbe a preponderance of 5 of convergence, 3 ofthe 8 dioptres of the power of the lens beingused up in overcoming the divergence of theincident beam.

Another Example /Suppose we are making a " magic lantern "

and wish to project our image on a wall aboutloft. away. We have a lens of 25 cm. focallength:

It is always easier if you draw a cleardiagram for these problems, as in Fig. 3.

An important fact to remember, which canoften greatly simplify calculations of this type,is that the path of light through an opticalsystem is reversible. We can, therefore,consider it as coming from the screen (S),diverging for 3 metres (divergence =ID)until it reaches the lens of plus 4 D). Itwill have a vergence on leaving the tens of-4 plus 4=-3f13. The reciprocal of thisgives us the object distance in metres ; it isobviously 3/II metres, or 27.27 cm. from thelens-rather too long to be satisfactory inpractice.

I do not propose to deal with concavelenses or convex mirrors, as it is only rarelythat these are required. Suffice it that if youhave a convex lens of too high a power it ispossible-but not always practical-to placeit in contact with a concave lens to give youthe required difference in power. If you havea plus 7 lens you can make this in effect aplus 6 by placing a minus r dioptre lens incontact with it. - Concave mirrors areoccasionally used for various purposes, though

February, 1948

they are not as satisfactory as a convex lens,generally speaking. I will give one exampleincorporating a concave mirror for readerswho are interested.

Concave MirrorsTake the case of a mirror of 24 cm. radius

of curvature. Its focal length will be halfthis distance, 12 cm., and its dioptric powerwill be plus 8.33 dioptres. If we place an

-0600

#8330

-..--'7-1330- &,77Metres Giving /mage Distance Ot

f27%.Fig. 4.-Diagram showing divergent light

impinging on a concave mirror.

object 2 metres from the mirror where will itsimage be found ?

Those readers who have grasped the basicprinciples of the vergence method of calcu-lating will have no difficulty in solving theproblem with the aid of the diagram (Fig. 4).Divergent light from the object 2 metresdistant ; dioptric vergence of this light is-0.50 dioptres. Impressed vergence of mirror=plus 8.33 D. Therefore, vergence ofreflected light will be plus 8.33 D minus o.5o D= -I-7.83 D. The reciprocal of 7.83, easilyfound from four -figure tables, is .x277metres. So the image will be found x2.77centimetres from the mirror. (By the way,those readers who are digging into reciprocaltables after a long rest from them must re-member to subtract the differences in the endcolumns.) If you require to project an imageon a screen the light after passing throughyour lens must always be convergent (plus).If your calculation gives you a minus resultyou must either use a stronger lens or increaseyour object distance.

MagnificationThe approximate magnification is very easy

to find-indeed, it is simply given by therelation of the image to the object distance.This is clearly illustrated in the followingexample :

You have a lens of 14 cm. focal length, andwish to project an image on a screen about6ft. away. What will be the object distancerequired and what will be the magnification ?

Here again, the problem is two-thirdssolved with the aid of a diagram (see Fig. 5).

Now that the method, has been shown indetail it will be encouraging to work thisproblem out without going into explanations,to illustrate its speed and simplicity.

(a) Incident light may be taken as travellingbackwards through the known distance, sothat we have :

Incident light divergingfrom 2 metres .. minus 0.50 D

Power of lens -1004 cm. plus 7.14 DDioptric vergence of emer-

gent beam .. plus 7.14minus o.5o D

+ 6.64 dioptresTherefore object distance

=(reciprocal of 6.64) = +15.o6 cm.(b) Magnification.

Object distance -15 cm. (near enough)Image distance = zoo cm.Therefore image will be 200'15 times the

size of the object, or about 131 times.Like reversibility of optical path, magnifica-

tion applies both ways round, too. It is bestto regard it, not simply as the number oftimes the image is larger than the object (itmay be smaller), but rather as the ratio ofthe image and the object distances. If theimage distance is three times that of the


object, then the image is three times the sizeof the object. On the other hand, if theimage distance is a quarter that of the object,the object is four times the size of the image,and so on.

I might add, by the way, that it is impossible'to calculate the magnifying power of- a lensused as a magnifying glass, or the magnifyingeffect of one's spectacles, in this simplemanner.

A Few Notes on Optical ModelsIt will be realised that there are serious

limitations to what the amateur can do whenconstructing optical models. To make acamera, for instance, that will give only apassably good picture, a first-class lens isrequired, and even the simplest telescope willgive a rainbow -coloured image unless anachromatic lens is used, the cost of whichmay be prohibitive.

Often, however, one can pick up a goodquality lens, either new or second-hand, whichwill do for an enlarger, magic lantern orepidiascope. A few hints on optical troublesyou may find in setting up such instrumentsyourself may be founduseful. If you are gettinga blurry image, you canoften improve the definitionenormously by " stoppingdawn "-that is, reducingthe aperture-of the lens.But this, of course, cutsdown the amount of lightto a corresponding extent,so that the degree to whichimprovement can be effectedby this means is limited.If a black -and -white picturecomes out with red andgreen edges on your screen,it is probably because yourlens is not achromatic andwill not give very good results whatever !Tou dowith it. If, however, the lens is for use, say,in an enlarger, you can incorporate a colouredfilter-say green-in the system, which willreduce the trouble appreciably and will makeno difference to the print. Your exposuretime, of course, will have to be lengthenedand, if possible, your illumination improved

(a)'RIF-.

(b)

hi

6.640.15

ObjectDistance(K)

163

in this case. It must be realised, however,that a lens has a different focal length forevery colour, and you will have to make afine adjustment to your object or imageposition to get the best results if colouredlight is used.

An epidiascope needs a large aperture lensand a strong light to get a worthwhile result,and the projecting lens should be fairly closeto the photograph if practicable. You willprobably find, with most amateur work, thatthe images are rather disappointing ; you mayalso find that if the centre is in focus the edgesare blurred, and if the edges are clear thecentre is blurred. All you can do about thisis to reduce the blurring as much as possibleby any of the means suggested, and set yourfocus somewhere in between the two positions,so that the whole is very slightly blurred.You will find your audience will not be nearlyso critical of your result as you are yourself.

A " magic lantern " needs a condensinglens as well as a projecting lens. The reasonis that it is most important to get the slideevenly illuminated, and unless a condensinglens is used you will find your image patchy.

7140

2m.-0.500

Image Distance (X)

Magnification- 230 . 13,5X

h

Fig. 5.-Diagrams illustrating the method of calculating objectdistance and magnification.

The source of light should be placed approxi-mately at the focal point of the condensinglens. Incidentally, if the condensing lens youhave is somewhat scratched, it does not matter,though the condition of the projecting lensshould be good. However, it is far better touse a good scratched lens than a perfectlyclear one of mediocre quality.

First British Commercial HelicopterAFEW months ago, when the world's

largest land -plane, the 126 -ton " BristolBrabazon I, was towed from its building siteat Filton to the new Assembly Hall for finalassembly, the Bristol Aeroplane Companyprovided a fitting signal to the world thatBritain was determined to capture airsupremacy over the oceanic routes. TheBristol Company has not, however, devotedits entire post-war energies to the construc-tion of trans -oceanic air -liners, for at theother end of the scale it has producedBritain's first commercial helicopter.

Designed as a four -seater and known as she" Bristol" Type 171, it is intended for useas an air -taxi, feeder -line aircraft, rescuework or artillery spotting. In building thishelicopter, the company has aimed at pro-ducing a " foolproof " aircraft, capable ofoperation not only by airlines but also bythe private individual.

Many safety features have been incor-porated in the design. Apart from the specialcontrols which give an outstandingly lightand vibration -free control, together with avery neat rotor head, a particular feature ofType 171 is the rotor itself, which has been

designed to have an unusual high moment ofinertia and to run at high r.p.m. This com-bination provides the rotor with a very highkinetic energy, which can be used in theevent of an engine failure to ensure a safeforced landing. 'One of the great dangers ofhelicopters in the past has been that in theevent of engine failure at a fairly -tow alti-tude, if insufficient height was available to putthe machine into an auto -rotating glide, therewere no means of preventing a very heavy orpossible crash landing. With the high kineticenergy of the Type 171 rotor, however,a safe landing is always possible because theenergy of the rotor can be used to destroy thesinking speed of the machine and still leaveit capable of hovering for a few secondsbefore touch -down, even with no enginepower.

Another feature of the " Bristol " 171 isthat it has been designed throughout with aview to long -service life with a minimum ofreplacements of working parts. This appliesparticularly to the transmission system, whereall parts, including the gears and bearings,have been designed for a life of to,000 run.ning hours.


A Radio Metal LocatorA Device for Finding Buried Metal

By J. COBHAM

THERE can be few radio experimenterswho have not at some time felt thedesire to stray dowp one of the side

tracks of radio and to' carry out tests withsome pieces of apparatus employing wirelessprinciples and materials, although not beingconcerned with communication.

With this thought in mind the followingapparatus was designed. The circuit wasfound to give excellent results, and manyinteresting experiments have been carried outwith it. Used on the sites of old Romancomps in Dorset, many coins, rings andother metallic objects were located, someof them of considerable value.

The CaseThis is a simple box constructed of thin

wood. It is fitted with a shelf on which thecomponents are mounted. The measure-ments of the case are not important and willobviously depend upon the size of the com-ponents to hand, and also whether one usesmidget valves or those of the more normal

L /ST OSC.

\t011

T

The Search CoilFrameThis was made of.

thin wood r6in. by14 -in. by 4 -in. deep.It is fixed to the bottomof the case by meansof small right-anglebrackets.

The, search coilwindings are as fol-lows:

L.1-7 turns of 3ogauge DCC wire.

L.2-9 turns of 3ogauge DCC wire.

A space of about half an inchleft between the windings.The Circuit

This employs three valves : The first is anoscillator, the second a combined detector -oscillator and the third a low -frequency out-put valve. This last may be a small power

t_ 0

Phones

2ND Osc.Det,

2.-Rear

should

LE Amp

Fig. r.-Circuit diagram for

size. If some of the very small valves canbe obtained and are used in conjunction withother miniature components, a really lightand compact unit can be made.

the radio metal locator.

H.7:÷

VariableResistor

view, showing components, and- the locator readyfor use.

be

HT-

L,T4

valve or a pentode.The coils for the det.-osc. stage are

wound on a former made from a small lengthof ebonite tube 'lin. in diameter.

L.3-5 turns of 3o_gauge DCC wire.L.4-18 turns of 3o gauge DCC wire.The following is a list of values of the

other components required:Condensers. Resistors.

A-.000r mf.B-.000r mf. R -3o ohm variable.C-000r mf. R.1-r meg.D-r mf.E-.002F-.00; mf.G-.000r mf.

variable.

OperationWhen the set has been completed it is

advisable, to test it out before it is put to anyserious use. This may be done by buryinga small sheet of metal such as copper a fewinches under the ground, "then with about6o volts H.T. adjust the tuning condenserand the variable resistor until a whistle isheard in the headphones. With the searchcoil held just _above the ground it will befound that the pitch of the whistle will alterwhen the apparatus is passed over the buriedmetal.

Transformer. -ratio.

RFC. -25 turns, 3oDCC on lin. former.

'ValvesWith regard to these, it is best to try out

several valves, as it has been found in prac-tice that one valve will not oscillate as wellas another, although they may both be ofthe same type and,'according to their markings, identical.

New British Standard for Screen BrightnessFor the Projection Millimetre Film (B.5.1404)

THE question of screen brightness wasunder consideration by a Committee

of the British Standards Institution in 1938and this work, which was interrupted by thewar, was resumed in 1945 when it was foundnecessary to examine the effect of the fol-lowing variations:

Type of film-It Was generally believedthat colour film required more light thanblack and white film for satisfactory pro-jection, but no very significant differencewas in fact found between the two. Theffect of fine-grain release, positive -film wasalso examined.

Distance of print.-For the average theatrea decrease of density gives an inferior resultowing to loss of tone -discrimination in thehigh -lights ; this factor was found to be

highly significant, but the problems involvedwere complex.

Contrast of the print.-A loss of tone -discrimination may be at least partially off-set by an increase of contrast and this factor,although less significant than density of'print was still important.

Projector arc and screen.-The most im-portant of these factors was the nature ofthe arc.

Auditorium lighting.-This affects projec-tion in two ways, the degree of dark adap-tation of the audience and the' tone -dis-crimination of the screen: reflected lightfrom the walls does; this is shown by thefact that the white screen is clearly visiblewhen the projector is shut down.

The problems arising 'from this factorwere also complex and some of these prob-

lems are awaiting attention by a B.S.I. Com-mittee, but the results showed that, underconditions where auditorium lighting wasalmost entirely -controlled by the nature ofthe scene projected, no significant variationof brightness levels were found to correspondwith changes in type of scene.

Subject.-The investigations show thatonly insignificant variations in optimurnbrightness levels resulted from the type ,ofscene being projected.

Result of investigations published.-Theseinvestigations, which were carried out by 4Committee of independent experts, yieldedvaluable results upon visibility of grain;flicker, glare and the general quality of pro-jection. Consideration of these results ledto the publication of B.S.14o4 which con:tains not only the Committee's recommen-dations but alto a comprehensive report onthe tests carried out and the results.

Copies of this Standard may be obtainedfrom Sales Department, British StandardsInstitution, 24, Victoria Street, London,S.W.s, price 2s. post free. .


An Electric Floor -lampConstructional Details of an Attractive and inexpensiveAppliance. By R. J. CHAMBERLAIN

USING a length of ordinary tubularbrass curtain rod as a column greatlysimplifies the construction of electric

floor lamps and the simple, modern type oflamp described in the present article shouldappeal to most handymen. A piece of rod4ft. 6ins. or 5ft. long is wanted. Its outsidediameter depends on the diameter of thenipple end of a lamp holder. This end hasto be a tight fit in the " bore " of the tubing.

As most bakelite holders, with push -barswitch, have nipple ends about in. diameter,the brass rod will be about sin. or possibly;in. in diameter. 'Therefore, as it is impera-tive that the holder' fits in the tubing, theholder must be obtained first, then tried incurtain rod of varying " bore " diametersuntil the correct size is found. Incidentally,

L..

/2"

it is always a good idea to bear in mind that;in the case of a slightly loose fit, the nippleend can be wrapped with a strip of insulationtape to build the correct diameter required.In the case of holders which are a trifle toolarge, the diameter can be reduced by filing.Try, however, to avoid having this job to do,as the bakelite is weakened near the shoulder-ing.

Other materials you will need consist of a9ft. length of twin flex, four I lin. diam.metal furniture gliders, some riin. by 6 (or8) flathead iron screws, a 6o -watt frostedlamp and the wood for making the base andcolumn shouldering. Regarding the lampshade and its holder, these are best pur-chased. The shade should be about 'bins.to i8ins. in diameter. Anything smaller,such as tzins., is out of proportion.

Fitting the Lamp HolderAs mentioned previously, the nipple end

of the lamp holder is fitted tightly into oneend of the brass rod, as sectioned at Fig. t,Having tested the holder in the rod, connectthe twin flex to its terminals, push the freeend of the wire doWn the rod and finally

force the holder home. A touch* of paintcould be applied to the nipple end of theholder to serve as a fixative.

It should be explained that the type oflamp holder suggested has a proper screw -offnipple. This enables the holder to be usedas a pendant (ceiling) type. For floor ortable lamps, the actual bakelite nipple isremoved so the end of the holder may screwon a brass adaptor plate affixed to the topend of the lamp column. As tubing is used,such a plate would be difficult to attach. Asthe rod is tubular and takes the nipple endof the holder, such a plate is unnecessary.

The Base and Shouldering -

The base measures I.:tins. by 14ins. by tins.It could be built up from zin. thick planking

Tins. wide by rub jointing two14in. lengths together. Forextra strength, the pieces maybe dowelled together, and thisis recommended.

Having levelled both sideswith a smoothing plane andcarefully trimmed the woodsquare with a try plane orblock plane, the corners areshaped as shown in Fig. 2.Note that the shaping con-forms with the position of themetal gliders. Simply gaugea zin. margin all round thetop side, then scribe the quar-ter circles with the compasses.With a tenon saw, make cutsin line with the marginal linesto the depth required 'and sawoff the corners, followingwhich the wood is roundedwith a wood chisel, paring offa little waste wood at a time

Fig r. (Left).-Side elevationand enlargeddetails of lathp-holder andtubular column.

until the shaping is correctfor filing and glasspapering.A lin. hole is bored throughthe centre of the base. Thisis the outlet hole for the flexwire.

A constructional view ofthe column shouldering- isshown in Fig. 2. It con-sists of a wooden socket,fitted with a skirting. Assum-ing the column rod is tin. indiameter, you require twopieces of wood t3ins. by tin.by lin. and two side piecesof similar length, but zins.by lin.

Glue and nail the narrow-er lengths between the- sides(using' slin. oval nails), thentry the curtain rod in thesquare socket hole. The rodshould be a neat fit and notwobble. Before adding theskirting pieces, make theupper base piece, this mea-suring 8ins. by 8ins. by tin.

The completed floor -lamp in a homely settingor ;inv., with a 2 -in. square hole into whichthe shouldering fits neatly.

Add the skirting pieces, these measuring8ins. long. Cut two tins. wide and .twoSins. wide from lin. stuff. Affix to theshouldering With glue and nails. A fewscrews should be driven through the upperbase piece into the skirting to give additionalstrength.

Affixing the BaseThread the twin flex through the tin. hole

in the base and proceed to attach the upperbase in position with screws, one being driveninto each corner via the underside of theheavier base. To facilitate handling and

(Continued on page 168)

14"

-1 2. I-;

- :

1

=_-

Fig. 2.=Underside view of base, collar piece, with constructionalview of shouldering to the brass tubular column.

166 NEWNES PRACT'CAL MECHANICS February, 1948

Davy or Stephenson ?The Priority of the Miner's Safety -lamp Invention

WHO originated the well-known miners'safety -lamp, that simple, foolproofefficient lighting device which, during

nearly a century and a half, has preservedinnumerable mine workers from sudden andtragic disaster? -

No doubt, if you follow the official historywhich is retailed in popular textbooks youwill aver that Sir Humphry Davy, theCornish chemist, the discoverer of sodiumand potassium, and also one of the pioneerelectrical experimenters in this country, is tobe credited with the honour of inventing thefirst successful miner's lantern, the devicewhich even to this day is known as the" Davy lamp."

But popular history, even when it dealswith inventions and discoveries, proceedsonly in broad outlines, neglecting significantdetails of a subject. It is, indeed, preciselyin the matter of the miner's safety -lamp in-vention that a good deal of credit has beenbestowed in the wrong quarter, for despitethe enormous success of the miner's hand -lamp constructed on the Davy principle, SirHumphry Davy himself cannot be said tohold priority in this invention. Anotherinventor, and one no less eminent than therenowned George Stephenson, the railwaypioneer, devised a form of mining lamp andactually used it in underground colliery work-ings some time previous to Davy's announce-ment of his invention.

The question'of the priority -a this import-ant and vital invention has been talked about,written about, argued and even quarrelledover since the first days of the miner's lamp.There have been Davy factions. and Stephen-son enthusiasts, neither of these beinginclined to admit the claims of the opposingparty. Hence the result has been that thehistorical matter of the priority of the miner'slamp invention has never been universally

Gas Exit

WaterSea/ Metal Chamber With

Silk Windows

.1- Air Entrance

Water Seal

The " wa er" lamp invented by Dr. ReidClanny in 1813. It preceded both the Davyand Stephenson lamps and was the first of all

miners' safety -lamps.

admitted. Such, indeed, is the position atthe present day. The Davy claimants, havinghad the greater influence, have been able toattribute the miner's lamp invention more orlesg solely to their hero, and to sidetrack theStephenson issue as one of little importance.

Let us, however, consider a few of, themore salient facts in this historical dispute,facts which are available to any inquirer whohas the time and the inclination to go to theirsources and sift them patiently for himself.

Dr. ClannyIn the first place, neither Davy nor

Stephenson was the originator of the miner'slamp. That honour goes to a certain Dr.Reid. Clanny, of, Sunderland, who, in t813,invented the -first of the miner's flame lamps.The Clanny lamp was an absolutely safe con-trivance and it extinguished itself automatic-ally in an atmosphere of inflammable gas. It

By J. F. STIRLING, .M.Sc.

comprised merely a suitably -mounted candlewhich was burned in an enclosed spice. Airwas fed to the lamp through a water sealbelow the candle and the products of com-bustion also had to pass through a water seal.

George Stephenson, creator of the " Geordy,"or first miner's lamp.

The necessary air was blown into the lampby means of a diminutive pair of bellowsactuated by a boy whose special duty thiswas.

But because the Clanny lamp was cumber-some, because it needed careful and continual'attention from the " bellows boy," and inconsequence of the great ease with which thecandle flame could be put out accidentally,Dr. Clanny's lamp never became accepted asa suitable illuminant for mine use. All thesame, it is to this rather mysterious Dr.Clanny that the fame of being the originatorof a mine safety -lamp rightly belongs.

George Stephen-son, it may be re-collected, at the timeof his earliest loco-motive trials, wasengaged as an en-gine wright at Kill-ingworth colliery,about seven milesnorth of Newcastle -on -Tyne. Previouslyhe had been abrakesman or eh-gine - attendant atother collieries inthe district and hewas well, familiarwith the many 'disas-trous "'blasts " orm i n e- explosionswhich, at that time,were increasing infrequency in theDurham and New-castle mining dis-tricts.

So dangerous weresome of these col-liery workings thatminers, driven to

desperation, refused at times to enter thepits, preferring, seemingly, economic and,indeed, actual physical starvation 'to a dailyencounter with pit perils which threatenedhourly to put an end to their existence.

" Blowers"Some of the mines were so bad that their

workings were full of " blowers " or fissuresin the coal seams through which inflammablemine gas escaped with a characteristic gush-ing noise. In these mines, naked candleswere utterly impossible. The phosphor-escence of decayed fish skins was tried as ameans of illumination, but it was of little use.In such mines the " steel mill wasemployed. This was a device in which anotched wheel revolved against a flint. Itstruck a stream of cold sparks which, it wasfound by experience, would not ignite thegas, and by this feeble illumination the Dur-ham and Northumberland miner carried onhis dangerous work.

There is an anecdote about GeorgeStephenson, aided by a few chosen men,bravely extinguishing a fire in the workingsof Killingworth colliery by building a wall ofbricks across the entry to the workings. Oneof the men, Kit Heppel, subsequently askedengineer Stephenson whether he thoughtthat something could be done to obviatethese continual mine explosions.

The answer which Stephenson gave wasthat he thought that something could be doneto this end.

" Then," ejaculated Kit Heppel, " thesooner you start, the better ; for the price ofcoal -mining now is pitmen's lives."

And that, if we are to believe records, ishow George Stephenson brought himself togrips with the pressing problem of construct-ing a lamp which would not fire mine gas inunderground workings.

The first idea of the afterwards celebratedlocomotive pioneer was that if he couldconstruct a lamp having an elongated chim-ney a current of air would continually ascendthrough the lamp ,and this would prevent theinflammable mine gas from descending downthe chimney and thus becoming ignited. Airwas admitted to the lamp through a narrowtube at its base, and Stephenson had a regu-

The rail -side cottage at Wylam, Northumberland, in which George. Stephenson was born, 1781.

a

February, 1948

lating slide fitted to this air tube so that hecould control the amount of air obtainingaccess to the interior of the lamp.

A Brave TrialIt was on October 21, 1815, that Stephen-

son received from Messrs. Hogg & Co., tin -men, of Newcastle -on -Tyne, the very firstsafety lamp which had ever been manufac-tured. It was 'a lamp which had been madeto Stephenson's own design.

Almost immediately, Stephenson subjectedhis lamp to practical test, a trial which, per-*haps, if it had failed, might easily have endedhis life abruptly and on the spot.

Taking a couple of colliery workers,Nicholas Wood and Jack Moodie, with him,Stephenson carried his new lamp down themine and into one of' the most dangerousworkings where explosive gas was issuingwith a loud noise from a fissure or " blower 'in the roof.

The men erected some deal boarding roundthat portion of the workings from whichthe gas was escaping, thereby making the airfouler than ever it had been before. Moodie,whose practical experience of fire -damp wasgreater than that of either of his companions,averred that it was suicide to enter into theboarded -up enclosure with any form of light.

But Stephenson declared his confidence inthe safety of his lamp. Leaving the othersbehind, he went boldly into the enclosure andheld his lamp up to the escaping gas. Theflame of the lamp grew bigger. Then itflickered aneP went out. But there was noexplosion.

In a distant part of the mine workings,Stephenson relighted his lamp. This timehis companions followed him into theboarded -off enclosure. Again, the same se-quence of events occurred. This time, notonly did the flame of the lamp grow bigger,but the lamp's interior seemed momentarilyto be filled with fire. However, the flamewas quickly extinguished and the lamp wentout.

Several times that night was the sameexperiment repeated. Always the same resulthappened. The problem of the mine safety -lamp had, in its essentials, been solved, andGeorge Stephenson knew it.

About a fortnight afterwards, Stephensonrepeated his experiments in the pit, this timein front of a larger number of interestedindividuals. As before, the lamp was entirelysuccessful. Not, of course, that the lampwas not capable of improvethent. Its fault

More famedpreserved by


was that it tended to become extinguished inthe presence of only traces of inflammablegas, and in such atmospheres it had to bevery steady and free from vibration.

Stephenson had an improved edition of hislamp made. This was tested and found to

better results. A third lamp was alsosubjected to tests in the mine on November3o, so that between October 21 and thelatter date Stephenson had designed and

Sir Humphry Davy, to whom popular historyhas accorded the chief fame of the safety -tamp

invention.

tested three safety -lamps of his own inven-tion.

The Sunderland CommitteeNow let us consider the Davy side of this

safety -lamp controversy.In the summer of 1815, a committee of

mineowners and their agents, alarmed at theincreasing frequency of colliery disasters inNorthumberland and Durham, sat at Sunder-land to consider ways and means of reducingthe hazards of mining. The committee satand talked, but found itself unable to do any-thing from a practical viewpoint. It did,however, recommend that Sir HumphryDavy, of London, should be approached in

the matter and that heshould be requested toturn his attention to thepossibility of devising asafe light for mines.

And that is how Davy.the chemist and elec-trician, came into 'themining world. Davy,at this time, was verymuch at the height of hiscareer and his fame. Hewas being lionised byLondon society. His ex-perimental genius waseverywhere admit t e d.His fame as a " chemicalphilosopher " was secondto none in Europe.

Quite unknown toStephenson, the greatDavy visited a number ofcoal mines near New-castle -on -Tyne on August24, 1815. He made arapid tour of inspectionand then departed. No

- doubt, one day in a col-as a locomotive engineer, Stephenson's memory is liery was enough for him.this memorial tablet set into the wall of his In London, Davy con -

birthplace cpttage at Wylam.t-

centrated on experiments.

167

His idea was to have a flame burningin an iron -mesh cage. Air is given freeaccess to the lamp and the products ofcombustion escape equally freely. In anexplosive atmosphere, the inflammable gaspasses through the gauze and is ignitedwithin the gauze cylinder surrounding theflame. The ignition, however, is unable topass beyond the metal gauze, the gauzethereby acting as a flame sieve.

Such was the principle which Sir Hum-phry Davy applied to the design of hit safetylamp. He announced his invention in a newhistoric paper entitled " On the Fire -dampof- Coal -Mines, and on Methods of Lightingthe Mine so as to Prevent its Explosion,"which he read before' the Royal Society ofLondon on November 9, 1815.

Davy seems to have conducted his experi-ments more or less'in secret. True it is thathe wrote a few letters to interested friendsin which he mentioned the progress of hisexperiments, but the fact remains that hisfirst demonstration of his experimental lamptook place during his Royal Society lectureon the date above mentioned.

By this time, Stephenson had designed andtested two of his safety lamps and was wellon the way to having a third lamp made..

Such are the facts, and they are facts whichclearly demonstrated the contention that,apart from the initial efforts of Dr. Clanny,it was Stephenson and not Davy who wasfirst in the field with the safety -lamp inven-tion. The time interval between the twoinventions was a small one, but the prioritywas undoubtedly Stephenson's.

The Davy lamp was rather simpler thanStephenson's, and gave a better light. More-over, it did not tend so greatly to go outin the presence of inflammable gas as didStephenson's lamp. But, of the two, theStephenson lamp, was rather safer, because ifthe wire gauze surrounding the flame in theDavy lamp became red hot, it then lost its

(Left). The original Davy lamp. (Right) TheStephenson lamp with its metal cover removed.

Qability to keep back the eternal spread offlame and in such circumstances it becameactually dangerous..

" Davy" and " Geordy "Davy's lamp won the day. If was pub-

licised extensively and popularly dubbed" the Davy." The Stephenson lamp, on theother hand, which became known as the" Geordy," was more or less restricted in useto the Northumberland -Durham collieries.

The rival claims of the " Davy " and the" Geordy " were hotly disputed, although,eventually, a synthesis of the two lamps wasbrought about. All the scientific people ofthe day, sided with Sir Humphry Davy, hisscientific reputation being so well established.The Davy faction affected supreme disdainfor Stephenson and his claims. Typical of

168

this attitude is the following passage extractedfrom Dr. Paris's " Life of Davy " (1830:

" It will hereafter be scarcely believedthat an invention so eminently philosophic,and which could never, have been derivedbut from the sterling treasury of science, -should ever have been claimed on behalfof an engine-wright of Killingworth, of thename of Stephenson-a person not evenprofessing a knowledge of the elements ofchemistry."In 1816, steps were taken to raise a sub-

scription for the purpose of making a suit-able presentation to " the inventor of the

The flame lamp displaced. An early accumu-lator electric lamp for mine illumination.


safety -lamp." Meetings were held in whichfeelings ran high. The claims of the Davylamp were well admitted by the Stephensonfaction, but the contention that Davy hadpriority in the invention was 'stoutly resisted.After a number of meetings had been held,the sum of £2,000 was ultimately presentedto Sir Humphry Davy as the inventor of thesafety -lamp and a purse of £ too was votedto George Stephenson " for what he hadaccomplished towards the invention." With-out any doubt, it was a case of Davy beinggiven the first prize and of Stephenson hav-ing to put up with the booby award !

Stephenson was, of course, uneducated andilliterate, although something of a naturalgenius. But, with the assistance of his son,Robert, the indomitable George put together

. a Written account of his activities and achieve-ments in the development of his safety -lamp.The document was printed and publishedand it subsequently appeared in the localpewspapers, the upshot of this publicity beingthat George Stephenson was entertained ata public dinner held in the NewcastleAssembly Rooms on January 18, 1818, andthere presented with the sum of it,000in testimony of his being the first to con-struct a practical safety -lamp for mining use.

And there Stephenson left the matter.After all, he had other and more spectacularinterests around him. He had already con-structed a successful locomotive engine whichwas to be seen running about daily at theKillingworth colliery. This had not beenheralded by articles in the newspapers andby eloquent lectures at the Royal Society,by fashionable cartoons and by variousreviews as were many of Davy's achieve-ments. It was a creation of his own brainwhich, he imagined, might ultimately servea much greater purpose than a mere collieryrunabout and which might, indeed, bedeveloped into a locomotive engine for use inconveying passengers from town to town.And to what extent Stephenson's dreams andimaginings came true we are all well aware.

Summing up, there is no doubt that both

February, 1948

Stephenson and Davy worked on theirrespective lamps independently and unknownto each other. Stephenson got in with hispractical lamp :Irst, but Davy, the fashion-able scientist of the day, had by far the betterbacking and the greater publicity. Therespective lamps possessed points of advan-tage and disadvantage over each other. Bydifferent routes, both the inventors arrivedat similar results, although, as old NicholasWood, the Northumbrian mine -worker andan excellent judge on colliery matters, onceremarked : " Davy's lamp is safe-butStephenson's is safer."

The modern safety -lamp as usedLancashire collieries.

AN ELECTRIC FLOOR -LAMP(Continued from page 165.)

screwing, the position of the upper baseshould be pencilled on the surface of themain base, then the screw holes bored andcountersunk at the underside. It will thenonly be a matter of positioning the upperbase, making starting holes with a bradawl,and driving home the screws.

It is assumed that all exposed nail headsin the woodwork are punched and coveredup with plastic wood or beaumontague (a hardwax filler). When the wood has been glass -papered smooth, it may be stained and pol-ished. A. light walnut finish is suitable. Itcan be obtained by brushing on severalapplications of light walnut french polish.Each application should be allowed to dry,then be rubbed down lightly with No. o orNo. oo grade glasspaper. Three separatecoats is sufficient. The final coat, of course,is not glasspapered.

To complete the work, fit a plug to theflex, and secure the latter to the undersideof the base with a suitable staple. The metalgliders are then. added. Use a frosted lamp,as there is too much glare from lamps havingclear glass envelopes.

It may be thought that, by having an 18in.diam. shade, the floor lamp will be top-heavy. Actually, the shades are very lightlymade up, and if desired, the main base couldbe lzins. square. If necessary, a 16in. shadecould be used with. this size of base. Bases,however, are seldom smaller than tzins.

square. When smaller, the base is usually" loaded " with lead, thereby counteractingany top -heaviness.

in

Report of NewStorage Battery

Club NoteRichmond and District Engineering

SocietyTHIS society has been formed with the

object of fostering interest in all aspectsof engineering and to provide a commonmeeting ground for engineers of all branches'within the various trades and professions.

Another .object is the presentation of lec-tures, talks, films, visits and exhibitions ofgeneral engineering interest.

Further particulars regarding membership,etc., can be obtained from J. W. Parton,hon. sec., 53, Onslow Road, Richmond,Surrey.

WORKSHOP CALCULATIONSTABLES AND FORMULA

Eighth Editionby F. J. CAMM

handbook dealing with methods of calcula-tion, solution to workshop problems, and therules and formula necessary in various work- --

'shop processes. It contains all the information .

a mechanic normally requires.From all booksellers, 6/- net,by post 6/6 from the publisher,

GEORGE NEWNES, LTD. (Book Dept.),Tower House, Southampton Street, W.C.z.

the

THIS report gives an outline of the basisof a new type of electrical storage

battery. Whilst the principle is well set out,the information is far from complete andconsiderable work would be necessary beforesuch batteries could be produced on a largescale.

The battery is reputed to have a cellpotential of 3-4 volts ; the cathode consistsof mercury or an amalgam retained behind aporous diaphragm such as a clay dell, whilstthe anode is a lead oxide grid. The aectro-lyte is a mixture of sodium hydroxide andsodium . sulphate solutions. On charge,sodium is deposited on the cathode and theanodic lead oxide is converted to the peroxide(which, incidentally, is termed superoxide inthe report). On discharge the reverse re-action takes place, sodium hydroxide beingreformed.

It is important to note that the cathodemust be specially shaped in order to preventself -discharge of the battery whilst on opencircuit. For further details, anyone interestedin this subject should refer to the F.I.A.T.report published by the Stationery Office.

This report is issued with the warning thatif the subject matter should be protected byBritish and/or U.S. Patents or Patent Applica-tions, this publication cannot be -held to giveany protection against action for infringement.


Electric Water Heatin PracticeConverting Existing Installations Various Types of Circulator : Thermostatic

SINGLE -HOLE fixing is widely adoptedfor copper cylinders (Fig. 6), sometypes being made for tinning and

soldering to the copper cylinder wall (Fig. 7).Sometimes it is necessary to use a template,and this is often provided by the manufac-turers.

Where drilling the tank is_ particularlydifficult or impossible and the tank capacityis larger than necessary, it is often possible tofix the immersion heater in the inspection

Fig. 6.-- (Above). Cut-away cylinder showing theposition of the circulatortype heater. Thermostatis enclosed in draughttube. Note the single holefixing of heater flange inthe top of the cylinder.(a) Non -soldering Essertype flange ; (b)" sweated " ring type.

Booster Heater

a

By G. A. T. BIJRDETT, A.M.I.I.A.(Continued from page 118, January issue)

cover. To do this, the cover is removed inthe normal way, the hole drilled and theheater screwed home. Inspection of theelement is then a simple operation. Beforeadopting this method, care must be taken toensure the tank contents, viz., water, abovethe element will meet the demands of thehousehold.

e

CirculatorsThese are fitted in the existing storage

tank and enable small quantities of hot waterto be drawn off soon after switching on.

They consist of an immersion -heaterelement surrounded by an outer sheath ordraught tube (Fig. 6). Water in contactwith the element circulates upwards insidethe draught tube and passes through a com-paratively small, hole at the top. This is

BThermostat

Controlusually too long and cannot be accommo-dated, but circulators, due to their length,will usually extend almost to the base of thetank, but rarely can be fitted in rectangulargalvanised tanks, which are n9t, of course,installed in, soft -water districts.

Other Types of CirculatorWhere there is little head room above a

cylinder and it is not possible to instal a con-ventional type of circulator which is fitted

Constant Heater

stored in the top of the tankand can be drawn off at once bythe user.

Circulators should, however,only be used in soft -water, nothard -water districts, as the venthole quickly becomes fouled withscale. In fact, circulators whichcan only be mounted verticallyare particularly adaptable in thesoft -water districts, for it is inthese areas where the cylindricalcopper tanks are largely fitted.These tanks have a height muchgreater than their diameter.

b Horizontal immersion heaters are

WM11110111111111111\

M1\11111111

g

Fig. 7.-Various types of circula-tor. (a) is a standard circulator;(b) has a booster heater com-

prising an additional elementto give a high loading and

therefore quicker heating.(c) is for externally fitting

to the water heater; and(d) is for horizontalfixing, which can be

used in cylinders orrectangulartanks ; (e)), (f)

and (g) showthe methods

of insialla-don.

This type ofheater is shownfitted in a cylin-drical tank inFig. 7(g).


be adequately lagged to prevent undue lossof heat and unnecessary consumption ofelectricity.

Lagging is generally carried out withgranulated cork. This, form is one of thecheapest and most effective methods of lag-ging a rectangular tank. Special pre-fabricated heat insulated jackets are, however,obtainable for both rectangular and cylin-.drical type tanks, and are wrapped round asa jacket (Fig. 8). Granulated cork can, ofcourse, be used for cylindrical tanks, whilean effective job can be achieved with an oldblanket or corrugated cardboard using

vertically in the top of the cylinder, two othertypes are available. These are: Side entrycirculators (Fig. 7d) and external circulators(Fig. 7c).

The side entry circulator consists of animmersion heater fitted horizontally in theside of the tank and a vertical extensiondraught tube which passes through the bodyof the tank and terminates near the top. Thishas an open outlet through which the hotwater circulates. As with the conventionaltype, small quantities of hot water can bedrawn off shortly after switching on theheater. A thermostat is usually incorporated.

a

not being used, the circulator can be fittedto them.

Two -element ConversionThis system has become a most popular

method of control. Two immersion heatersare installed in the tank, one at the bottowwith a loading or 2-3kW. and one of 'kW.near the top of the tank. These can becontrolled by separate thermostats, thoughhand control may be used. but is, of course,less satisfactory.

For all normal use the smaller heater atthe top may be used. Small quantities of

e

Fig. 8.-Various types of cylinder and tank lagging. (a) (b) and (c) are special jackets whichcan be purchased and tied on the cylinder or tank ; (d) shows how a wood framework can bebuilt around a tank and filled with cork granules ; and (e) a similar method of lagging a cylinder.

These, like all circulators, should not beinstalled in hard -water districts owing to thescale which is likely to form in the smalldraught -tube outlet.

External CirculatorThese are fitted externally to the side of

the tank or cylinder. Two holes are boredin the tank, into which flanges are insertedor " sweated " and the heater is screwed on(Fig. 7f). If the cylinder is fitted with boilerflow and return connections and these are

water for washing and washing up can bedrawn off, but when a bath is required thelower heater is also brought into operation,when the whole contents are heated. Chiefadvantage of this method is the saving inrunning costs, since, as only part of the tankcontents are normally heated, losses -are there-fore reduced to a minimum. It is necessaryenly to lag the top portion.

LaggingA converted electric hot-water tank should

d

several layers over which is sewn acanvas cover.

Before applying granulated corkto a rectangular tank, a frame ofmatchboard should be built, leav-ing a space of at least tins. betweenthe tank and woodwork for pour-ing in the cork. This is thenrammed in firmly and evenly(Fig. 8d) and an effective heat insu-lator is thus made.

Heat losses from a lagged tank(3ins. of granulated cork) where thetemperature of the water is 180deg. Fahr., are approximately 4waifs per sq. ft. of surface area.Heat losses, on the other hand,from an Unlagged tank where thewater temperature is r8o deg. Fahr.are between 36 and 72 watts persq. ft.

Immersion HeaterImmersion heaters are made in

various electrical loadings from soowatts up to 6 kW. (6,000 W.). Sizeof heater to install depends oncapacity of tank, whether thermo-statically or hand controlled and, ifhand controlled, the time which isto be allowed to heat up the tank'scapacity from cold. Maximumloading in an individual case alsodepends upon the electricity supplyauthority's regulations. Someauthorities require a low loading.

Calculating Optimum Size of ElementThe average hot water tank has a capacity

of between 20 to 3o gallons. One 2 kW.heater where a thermostat is incorporatedis usually sufficient, but with hand controla 3 or 4 kW. heater should be used.

Some knowledge of the mechanism of heatand electricity is, however, necessary todetermine the optimum loading in a givencase.

(To be continued.)


THE WORLD OF MODELSNottingham Exhibition of Models00 Gauge Permanent Way

: Model -making Activities in Barnstaple : NewBy "MOTILUS"principal' award, the " Pool Trophy," forhis lin. scale "Princess, Royal." Othernotable awards were the " Wallis Binch "Challenge pup to Mr. J. Tilson for hiswatchmaker's lathe, and the " Syne anpnyme"cup to Mr. J. Witty for his 21in. gaugeL.N:E.R. " Flying Scotsman."

As well as the excellent locomotive models,there were many other varied items to catchthe eye of all modeltmakers, in whateverspecial branch, of the hobby they were inter-ested. Not least arnong these was Mr.S. J. Bradley's under -type engine and boiler,shown in Fig. 3. The Nottingham ModelYacht Club also had a good display of modelsailing yachts and boat hulls of several types.(Fig. 4.)

Fig. t. Mr. Barkes' fin. scale L.M.S.locomotive, " Princess Royal," used on therunning track at the Nottingham Society's

Exhibition last March.(Photo by Reginald Clarke, Nottingham.)

AT the end of March the NottinghamSociety of Model and ExperimentalEngineers will be holding their

twelfth annual exhibition. Those who hadthe opportunity of seeing the exhibition lastyear, already have an idea of the splendiddisplay of models that this society can pro-duce. Full particulars of this year's exhibi-tion, which is to be held from March 31stuntil April 3rd, can be obtained from theHon. Secretary, Mr. E. S. Wright, 186, Wil-ford Road, Nottingham.

I think this is a good opportunity to saya little more about the Nottingham society'sshow last March and some of the two hun-

Fig. 3.-Mr. S. J. Bradley's compound, under -type engine and boiler, awarded a certificate ofmerit for good workmanship at th& Nottingham

Society's Exhibition last March.(Photo by Reginald Clarke, Nottingham.)

dyed models gathered there. Out of fivethousand visitors, some two thousand chil-dren enjoyed rides on the multi -gauge pas-senger -carrying railway. - Three locomotiveswere used on the track: the society's 5in.gauge o -6-o goods engine, Mr. J. Barkes'31in. gauge " Princess Royal," and Mr.Ruffle's " Flying Scotsman." The twolatter engines are illustrated here (Figs.and z). Mr. Barkes was awarded the society's

Fig. 2 (Above).-Mr.Ruffle's tin. scale, 21in.gauge, " Flying Scots-man," also used on theNottingham Society's

running track.(Photo by Reginald

Clarke, Nottingham.)

Mention of just these few exhibits, withthe accompanying illustrations, will convincereaders that this exhibition is well worth avisit if they are within reach of Nottinghambetween March 31st and April 3rd. Even if'you have to come from far afield, you will bewell rewarded by making a pilgrimage to

Fig. 4.-A group of sailing yachts and boat hulls of various types, displayed by the Notting-ham Model Yacht Club on their stand at the Exhibition.

(Photo by Reginald Clarke, Nottingham.)1

172

Victoria Baths, Sneinton, where the exhibi-tion is to be held. Mr. Wright has told methat the society are extending an invitation toall model engineers to enter the open com-petition held in conjunction with the exhi-bition, for which they are offering their usualprizes of 5 guineas, 3 guineas and 2 guineas.Model -making in Barnstaple

While spending a short while in Barnstaple,North Devon, recently. I noticed in the


what he has told me, I feel sure it will bea success. The intention is to launch thisclub with a local exhibition of models, andto get some of the influential residents inBarnstaple to give act. ve support to the ven-ture.

"Puffin Building Books"Almost everyone is familiar now with the

Penguin, Pelican and Puffin books that areto be seen brightening every bookstall, and

Fig. 6.-Another view of the model CotsWoldvillage, showing the stream, bridge and railwaystation. The piece of ibo gauge permanent waytrack is the new, realistic, " Peco-Way."

Athenaeum museum there a good model ofa steam winding engine, made by Wm.Sparks, of Pilton. Mr. Sparks was awardeda medal at the exhibition of the Agriculturaland Industrial Association of Queensland,Australia, in 1894. This is an excellent pieceof amateur workmanship and makes a wel-come contribution to the small but well -arranged museum at Barnstaple.

Shortly after I had examined this engineI found I had the opportunity of a brief meet-ing with Mr. J. S. Hutchinson, of Barn-staple, who is a keen model -maker, now en-gaged in building a tin. scale, coal-fired,4-6-2 locomotive, to the designs of" L.B.S.C." Mr. Hutchinson has convertedone of the rooms in his home into a well-equipped workshop and the .loctimotive hadreached a stage where it was possible to ex-amine the fine workmanship put into themodel. Mr. Hutchinson has promised mesome photographs, showing various stages inthe construction of his model, which I hopeto include in a later article.

I was pleased to learn that Mr. Hutchinsonis gathering a few enthusiastic friends toform a local Model Engineer Club. From

Fig. 7.-Section of " Peco-Way" oo gauge track, showing detail.

February, 1948

stone walls. The railway station is fencedoff with a wooden paling, where you canimagine small boys running from the villageschoolroom to perch themselves, regardlessof discomfort, watching the Midland ex-presses rush past, heedless of the quiet peacethey so rudely disturb for a short space.

Margaret and Alexander Potter contributesome very pleasing sketches and notes toassist in the cutting out, folding'and erec-tion of the model. I am fortunate in hav-ing a friend who is keen on architecturalmodels of this kind. The two illustrations,Figs. 5 and 6, show different views of thecomplet4 village, after my friend had builtit and, aided by the black and whitesketches, added some imaginative improve-ments in the way of trees, lawns and animpression of water in the stream, whichheightened the realism of his model. Hemounted it all on a base, 2ft. 6in. by 3ft.The piece of railway track you can see inthe foreground of Fig. 6 was not taken fromthe " Puffin Building Books," but is a pieceof " Peco-Way " 00 gauge permanent way.

"Peco-Way" 00 Gauge TrackTalking of Peco-Way, I wonder how many

readers are conversant with, this very realisticnew form of 00 gauge permanent way.It is now becoming ver3, popular among

11111Mm"

Fig. 5.-:The model Cisuold village, built up from the three new " Puffin Building Books,"

on all booksellers' shelves. I am pleased tosee some new publications now on sale, the" Puffin Building Books." The first three ofthis series, numbered 1A, il3 and IC (price2s: tod. each, including tax), are to enablemodellers to build a miniature Cotswold vil-,lage, from cut-out drawings in the book.More than this; the completed model is to ascale of 4 mm. to the foot, which is thestandard 00 gauge scale. Here is a chancefor 00 gauge fans to enrich their railwaylayout with characteristic scenery. I donot think a better choice could have beenmade for all who know and love the pleas-ant, mellowed atmosphere of the Cotswold

villages. The cut-out drawings inthese books havebeen planned by anarchitect, Mr. L. A.Dovey, who isfamiliar with thematured stone build-ings in the Cots-wolds. Here in thesebooks you will findall the features asso-ciated with anEnglish village: thecottages, the church,the village hall, theinn and the waysiderailway station. Here,too, are the stream,spanned by a simplestone bridge, and the

' paved village street,edged with the old

00 gauge enthusiasts Who demand real-ism as a feature of their track. Fig.7 gives a close-up of a section of a railwaylaid with this track, including a pair ofpoints. Centre or side rail for electric trac-tion may, of course, be added if you requireit. The main new feature in this track isthe base, which is of special card with thesleepers embossed on it, darkly coloured, andpierced ready to receive the chairs. M.E.T.A.standard nickel silver rail is used. If youare interested in Peco-Way, you can obtainfurther information about it from Messrs.Bassett-Lowke, Ltd., at their branch at 112,High Holborn, London, W.C.r, or by postfrom the Head Office and Works at North-ampton.

I have just heard that Messrs. Bassett-Lowke also have some news for shin model-lers. They are shortly issuing a new cata-logue devoted entirely to ship models, fittings,parts and all accessories for the model shipbuilder. The catalogue is now with theprinters, and should be available by the timethis journal.is in your hands, ready for youto start building in preparation for the sum-mer season.

A NEW VEST POCKET BOOK

NEWNES METRIC &DECIMAL TABLES

By F. J. CAMM316 or 3/9 by post from

Geo. Newnes, Ltd., Tower House,Southampton St., Strand, W.C.2.


Trade NotesThe "Handyman" Anvil

THIS sturdy anvil has been produced tomeet the demand for a small anvil suit-

able for engineering enthusiasts, modelmakers, and handymen. Made by the manu-facturers of the well-known Coburn range ofanvils, the " Handyman " anvil is of solid

The " Handyman" anvil.high carbon cast steel with flame -hardenedworking surface. Further particulars areobtainable from K. and L. Steelfounders andEngineers, Ltd., Letchworth, Herts.

The "Beatrice" Piano ConditionerTHIS electric conditioner is designed for

the purpose of keeping a piano in per-fect playing condition. This it does bymaintaining the interior of the piano at anaverage temperature of 6o to 65 deg. Fahr.,thus drying out all dampness from the operat-ing mechanism. It also has the effect ofpreventing " bloom," so keeping the exteriorof the piano case in a highly polished condi'-tion.

The conditioner, which is 71 -in. long, .3ins.high and 2.1ins. wide, is supplied completewith 2 yards of 3 core cable, power plug andsocket, and fixing wood screws. (Extra cablewill be supplied, if desired, at is. per yard).The aluminium alloy case is designed to pre-vent accidental or intended insertion offoreign bodies, and to be dustproof, yet toallow free circulation of air. The metal caseof the conditioner being earthed and comply-ing with electricity regulations. The instru-ment is designed to be coupled through thepower plug and socket continually to themains (220-25o volts) A.G. or D.C. and con-sumes only 3o watts per hour.

It is easily fitted in the lower right handcorner of the upright type of piano, screwedto the baseboards, and in the case of grand

and baby grand pianos is fitted beneath thepiano case at the top of the pedal column.Full fitting instructions are enclosed with eachconditioner.

Particulars as to price, etc.,can be obtainedfrom B. Whittaker, 252, ury New Road,Heywood, Lancs.

(Right) ThePrestacon Pressand accessories.

The Prestacon PressTHE Prestacon Press is a precision tool that

will appeal to. all model -makers andhome handycraftsmen. It will pierce roundand square holes in sheet metal, rout larger holes or straight slots and bend metal stripand plate to any angles up to 45 deg.

The " Beatrice" electric piano conditioner.

Civil Aviation News" Bristol" Hercules on Show in

MelbournePROMINENT among stands designed to

give British industry a boost at therecent Royal Melbourne Agricultural Showwas that of the Atlantic Oil Co., featuringa section model of the " Bristol " Hercules63o sleeve valve engine.

Mounted on a railed, circular stand, theengine stood in front of a strikingly effectivebackcloth showing Herculean figures at workat the glowing forge of Industry.

The stand was the centre of .attractionfor thousands of Australians who flockedto Melbourne for the show-the mostimportant event in the calendar of theAustralian agricultUral world

Freighter's 35,000 Miles Trip

"UNDOUBTEDLY one of the larIe'st

and most ambitious air -freightingprojects ever undertaken since the early daysin New Guinea " . . . in these words, Mr.G. D. Nicoll, manager of the Aircraft Divi-sion of the Overseas Corporation (Australia),Ltd., summed up the latest exploit of the" Bristol " Freighter, Merchant Venturer,which, after a successful 35,000 milesdemonstration tour of Australia and NewZealand, is now in charter service withAnsett Airways Pty., Ltd.

The project was delivery by air fromMelbourne to Launceston, Tasmania, of afleet of ten passenger tourist coaches urgentlyrequired for the summer season. Tours

All these operations 'can be carried out atany position on a metal plate and each opera-tion can be reproduced on any number ofplates with complete accuracy. This is dueto an ingenious arrangement of indexed holesinto which the " location " or " guide " barsfit at right angles to each other. These, guidebars form set edges against which the metalfor working is placed. No measurementshave to be made by the operator and it takes

only a few seconds to change the positionof the metal or the operation of the press.The guide bars also provide for a " minus "working which allows for metal thicknesswhen bending or when piercing holes tomatch inside an angle.

With the aid of this handy tool, whichbrings workshop, practicewithin reach of everymodel - maker, variousmetal parts can be madeinto. an unlimited range ofmodels.

A comprehensive Pres-tacon outfit includes: Allnecessary tools, guidebars, piercing punched,dies, forming die span-ner, screwdriver, metalplates, strips and angles.

urther particulars areobtainable from L. Reesand Co., Ltd., 31-35,Wilson Street, London,E.C.2.

had already been arranged, and it was there-fore essential that the operators, PioneerCoaches Pty., Ltd., should have at least sixof the vehicles delivered by October s.

Unable to obtain shipment by sea becauseof the - widespread strikes and shorthe ofshipping, Pioneer Coaches, Ltd., appealed -to the Overseas Corporation-the BristolAeroplane Company's Australian agents-forassistance. Aid was readily given and,thanks to the versatile Freighter, the entirefleet of ten coaches was delivered beforethe end of September. In a series of twice -daily flights from Essendon Airport, Mel-bourne, the Freighter crossed the Bass Straitto Launceston, carrying on each flight onecoach 22ft. in length and weighing 6,000lb.,plus an additional t,000lb. of freight. Onthe return trips the aircraft carried on eachoccasion a freight load of approximately7,000lb. of miscellaneous merchandise.


Letters from ReadersTrisecting An AngleSIR,-Why do the people imagine such

a vain thing ? It is impossible to trisectan angle by Euclidean geometry.

The construction suggested by R. E.Brett in your December issue is based on anincorrect assumption to which hs lends anair of truth by stating that " it is well known."

If the base of an isosceles triangle bedivided into two parts of ratio m : i thenthe angles subtended at the apex will havetheir sines in the same ratio. This cannot beextended to more than two parts.

Examine his Fig. 2. The triangles ABPand APQ have the same height and bases ofequal length. Therefore, their areas areequal. But the area of a triangle can alsobe expressed as ab sin C., i.e.,

AB AP sin BAP -1 AP AQ sin PAQ.Now AP is common and AB and AQ areobviously not equal in length. Therefore,the angles BAP and PAQ cannot be equal.-M. C. MOORE (Epsom).

The CinegramSIR,-I recently read in the October issue

of PRACTICAL MECHANICS an article byMr. F. Townsend Pamment on the Cinegramwhich I found most interesting, but for whichI would suggest a slight improvement.Instead of having an oscillating mirror(G, Fig. 3) it should have a series of rotatingmirrors, i.e., a revolving wheel driven by ashaft at right -angles to the spindle (R) and

driven by the bevel gear (N), revolving at thesame speed as the turntable (M), having onits edge a series of mirrors suitably set. Eachof them would follow the image the same wayas the oscillating mirror, but at the end,instead of flicking back, would be replacedby the next one, that would now pick up thenext image, and so on.

This would give a much steadier image onthe screen, as practically there would be nointerruption between the images and noflickering, and would be easier to regulate.

The new shaft or spindle should have asquare or T -section and a free longitudinalmovement through the centre of the revolvingwheel with the mirrors, to allow for theforward movement of the turntable, and sobe always centred under the tone-arm.-DR. ANTONIO LEITH MONTEIRO (Funchal,Madeira Island).

Synthetic FatsSIR,-I found the article on fats by J. F.

Stirling (November, 5947, issue) veryinteresting as I have had actual experienceof the ersatz margarine named " Prima "which he mentions as being issued to theGerman forces.

During the occupation of Guernsey Iworked in the German food store, and whenthe stocks of French butter ran out we gota stock of this margarine in 25o grammepackets. I used plenty of it at home andhad no complaints regarding taste from

friends to whom I gave

-.)

Off -setMirrors

Cinegram movement with rotating mirror wheel.

Apackets. Of course, thismay have been because itwas a welcome gift, anykind of fat was, but, per-sonally, I found it all right,particularly for makingchips.

That was in 1941-2, but'ater, in 5944-5 we hadsome issued to us in theinternment camp I wasthen in.

An interesting sidelighton the German stocks offats is that towards the endof 1944 the Commandanttold us that we would haveto have our fat ration ofbutter, as no more margar-

ine was available. I suppose they needed it allfor war purposes.-E. WEBSTER (Brighouse).

An Effective Alarm

t.)IR,-I was very interested in C. Brad-

shaw's practical method of contrivingan alarm which appeared -in the Decemberissue of PRACTICAL MECHANICS.

I would like to improve on this by usinga three -terminal, continuous ringing bell,thus eliminating one or two disadvantages,such as the newspaper coming in too far, andthe possibility of it getting wet in bad weather.

The accompanying diagram explains itself.After the newspaper has fallen to the floorthe bell will still continue to ring, until thecord is pulled to replace the trip.

These bells are very little dearer than theordinary bell and are obtainable at mostelectrical supplies shops.-H. WILLIAMS(B.A.O.R.).

An alarm circuit

Books ReceivedMotor Cycling Manual (12th Edition).

By the Staff of " Motor Cycling."Published by Temple Press, Ltd. i6opages. Price 5s. net.THE purpose of this useful manual is to

provide the newcomer with a ground-.work of knowledge which should make himself-reliant and conversant with technicalterms, which are usually puzzling to thebeginner. The intricacies of construction andoperation are explained in a manner which iseasily understandable by the most un-mechanically-minded novice, whilst at thesame time being satisfactory to the mostexacting enthusiast. There are also chapterson such practical problems as " vetting " asecond-hand machine, and hints on the road -craft which distinguishes the really efficientrider from the novice.

Among other noteworthy features of thismanual are the many excellent line drawingswhich illustrate it.

Let's Take a Photograph ! By G. J.Matson. Published by Thomas Nelson& Sons, Ltd. 212 pages. Price 7s. 6d.net.THE beginner with a camera need have no

fears if he has this interesting and usefulbook to help him with his first experiments inthe realm of photography. The subjectMatter covers the whole art in simple and clearlanguage, from descriptions of the varioustypes of cameras to developing, printing andenlarging. The book is illustrated withnumerous photographs and diagrams.

Electrical Engineering. By Frederick W.Purse. Published by Southern EditorialSyndicate, Ltd. 104 pages. Price5s. net.THIS book, which deals with the scope,

training and prospects of electricalengineering as a career, caters -primarilyprimarily foryoung students of both sexes who are aiming

Circuit Breaker Switch

---.---1

Switch OnLetter Bar

with continuous ringing hell.

for one of the higher posts in the profession.There are nine chapters under the headings :Electricity in Retrospect ; Various Aspects ofElectrical Engineering; Preliminary Decisions;Foundation Studies and Training ; Career tobe Adopted; Successive Progress.; GeneralProspects ; Ultimate Aim ; and LookingAhead.

In addition to students, anyone comingwithin the scope of electrical engineering willfind this book interesting reading.

NEWNES ENGINEER'SPOCKET BOOK

By F. J. C.41111

10/6 or by post Hi-Obta;nabk from booksellers, or by post fromGeorge Newnes, Ltd., (Book Dept.), Tower House,

Southampton Street, Strand, London, W.C.2.

February, 1948 NEWNES, PRACTICAL MECHANICS 175

Ns

QUERIESENQUIRIESA stamped addressed envelope, three pennystamps, and the query coupon from the currentissue, which appears on page 32 (THE CYCLIST),must be enclosed with every letter containing aquery. Every query and drawing which is sentmust bear the name and address of the reader.Send your queries to the Editor, PRACTICALMECHANICS, Geo. Newnes, Ltd., Tower House,Southampton Street, Strand, London, W.C.2.

Experimental BatteryT HAVE a drawing of an experimental apparatus

for producing electric current by aluminiumand copper plates revolving half -immersed in" a liquid." Would the liquid, or electrolyte, bechromic acid ? Can you suggest any betterelectrolyte for this purpose ?-R. Wright (GoldersGreen).WE are afraid that, with such meagre details of your

experimental project, we cannot be of muchassistance to you. The electrolyte would certainlynot be chromic acid since this would rapidly destroythe metal.

We consider that a solution of sodium phosphate(say, r part in 3 of water) would provide a more adaptableelectrolyte. A similar solution of sodium metasilicatemight also be useful, or even a very dilute solution ofhydrochloric acid. You might also try solutions ofcitric and tartaric acids.

All these suggestions of ours, however, are purelytentative ones, and, in the circumstances, we cannotpossibly guarantee their success.

Any of the above materials may be obtained fromchemical houses, as, for example, Messrs. Griffin andTatlock, Ltd., Kemble Street, Kingsway, W.C.2 ;Messrs. Hopkins and Williams, Ltd., 16-17, St. CrossStreet, Hatton Garden, E.C.r ; or Messrs. Vicsonsand Co., :48, Pinner Road, Harrow, Middlesex,if not, through, or from, your local druggist.

" Ferrotype" ProcessCAN you advise me on the following matter :

I would like to know what are the solutionsused by the street photographers who produce aprint in one minute. I understand the " plate "is bromide paper.

I have tried many reversal solutions and findthat the results are poor. Would you also giveme working details of the camera used and theaddress of a manufacturer who supplies cameraand solutions. -L. Clancey (Mottingham).THE street photographers to whom you refer operate

the old ferrotype " process, or a modificationof it. Originally, this process gave direct positiveson enamelled iron plates which were coated with a veryrich silver emulsion. Nowadays, paper is substitutedfor the metal plates.

Ferrotype cameras 'and materials can be obtainedthrough any of the big photographic dealers, such asMessrs. Jonathan Fallowfield, Ltd., Newman Street,London, Wa ; or Messrs. Wallace Heaton, Ltd.,Bond Street, London, W.r.

The image is not reversed. It is developed up as apositive in a single operation. Developers vary, butthe following is a typical one :Sodium carbonate .. 4oz. or 200 grams.Sodium sulphite .. 20Z. too grams.Hydroquinone }oz. 12.5 grams.Potassium bromide .. 290 grains 29 grams.Hypo solution (as below) IOZ. 25c.cs.Warm water to.. .. zooz. r,000c.cs.Allow the above to stand for two days. Then pouroff the clear solution for use. In cold weather, useonly half the above quantity of potassium bromide.

The fixing solution is made by dissolving 4oz. ofhypo in 200Z. of water.

Development of the exposed plate or paper normallytakes 8 to 12 seconds in hot weather; 12 to 20 secondsin cold weather. The plate is then momentarily rinsedin water (if practicable) lnd fixed in the above fixingsolution for zo to 3o seconds. It is finally rinsed.

Note that in this ferrotype process the image isalways reversed in relation to right and left. Usually,however, this is quite immaterial.

Waterproof DistemperCAN you tell me how to make a waterproof

whitewash mixture ? I wish to use this out-doors. My objection to marketed brands is thehigh cost. -Norman James (Orpington).DISTEMPER paints nowadays are expensive on

account of the high cost of the casein compoundwhich is put into them. On this casein depends thewater -resisting properties of the colourwash. Hence,at the present time, a dependable distemper cannotpossibly be made cheaply.

Distempers have varying formulae, many of themsecret. They all contain casein, however. or some simi-

lar and related compound. The following is a typicalformula:

Casein .. .. too parts

Urea 34 3,HexamineLithoponeZinc oxideLime .. 50

The above gives a white distemper. It may be colouredby replacing the zinc oxide with mineral colours.

Unfortunately, you will hardly be able to make up theabove formula for yourself since casein, which isindispensable, is extremely difficult to obtain.

By dissolving glue in an ordinary whitewash mixture,a certain amount of extra binding power is given to thewhitewash, but the material is not waterproof in thestrict sense of the term. For outdoor use, such materialmight, however, last a season. The amount of gluedissolved should be about 5 per cent. of the volume ofwater used to make the whitewash.

Filler for Woodwork : Mixing Paints(T\ COULD you please inform me how I couldAi make a filler for motor -car bodywork,mudguards and woodwork which could beflattened with a pumice block ?

(z) I have a can of azure blue paint ; how canI change it to a wedgwood-blue shade ?-J. W.Howie (Glasgow).

\ A MIXTURE of equal parts of whiting and fine) silica dust makes an excellent filler for woodwork

when moistened with a little thin oil. For metalworkand car bodywork generally, the following filler mediumis better :

Rubbing varnish 2 gallons. 'Boiled linseed oil .. Z gallon.Japan varnish gallon.Finest silica .. 41b.White lead .. 41b.Aluminium silicate .. 20 ozs.

The aluminium silicate has a flaky structure whichmakes it so suitable for filler purposes. Whiting,however, may be substituted, but not quite with thesame results.

(2) It is quite impossible for us to give you directinstructions to bring about the colour change whichyou desire, since there are so many shades or varietiesof the two blues which you mention. Moreover, paintsdo not readily permit uniform colour changes withoutsome process of regrinding the colour into the paint.Your best plan will be to mix together ultramarine blue,3 parts ; white lead, 12 parts ; lemon -chrome yellow,r part, and then to work this mixture very slowly andcautiously into your misting paint.

Fluorescent Sign on GlassT WISH to make a fluorescent sign on glass to

hang in a shop window.Would you please inform me as to how to go

about it, and what type of electric bulb is requiredto make the sign become fluorescent ?-D.Delany (Leis, Eire).TO obtain a fluorescent effect from certain fluorescent

substances you must have a source of lightcontaining ultra -violet rays. Ordinary incandescentelectric bulbs do not emit these rays. You must haveeither a mercury -vapour lamp, an arc lamp, or a dis-charge type of lamp emitting ultra -violet rays. No othervariety of artificial light will bring about fluorescence.

The fluorescent material is dissolved either in wateror spirit and painted on the glass or, if it is insoluble,it is finely powdered and mixed with gum water or agum arabic solution and then painted on the glass.After drying, the glass thus treated is placed in the pathof the rays from the special electrical device, whereuponthe painted areas fluoresce so long as the exciting raysare emitted from the electrical device.

To obtain a source of ultra -violet light your bestplan, we think, is to consult one of our advertisers inelectrical materials, or, alternatively, to apply to one ofthe large firms of electrical fittings dealers.

Anodes for Silver PlatingWILL you kindly give me the following

information ?(a) Can I use old sterling silver articles for

plating direct on to new work ?(2) Should this not be possible, will you

explain how I can recover silver and render itsuitable for use as anodes ?

(3) Can you also give a method for indicatingthe amount of silver deposited ?-D. J. Easter-brooke (Exeter).

\ ANODES for a silver-plating bath must (or should)be of fine silver, not sterling silver. Sterling

silver contains 7.5 per cent. of copper. This copperwould find its way into the bath and upset its chemicalbalance. For occasional silver-plating, sterling silveranodes can be used, but for any regular work fine silveranodes must be employed.

Suitable anodes of fine silver can be purchased fromMessrs. Wm. Canning & Co., Ltd., Great HamptonStreet, Birmingham. They are not very expensive.

(z) It is not easy to convert sterling silver into finesilver, and the trouble and cost renders the process notworth while in the majority of instances. The sterlingsilver is dissolved in warm dilute nitric acid, and thesolution of silver nitrate which results is filtered. Dilutehydrochloric acid is added. This precipitates thesilver as white silver chloride. This is filtered, washedon the filter, and suspended in water through which astream of hydrogen is passed. The silver chloride isreduced to silver which is deposited in a black, powdery -form. This is collected, washed, dried and then fusedat a near -white heat under a layer of borax and sodiumcarbonate. A silver " button results at the bottomof the crucible

From the above description you will, we think, agreethat the process is a tedious one and that it calls for agood deal of chemical knowledge, to say nothing ofexperience and practical skill.

(3) There are several methods of indicating theamount of silver deposited in a plating operation, butthey are all somewhat complicated, and for theirdescription we must refer you to a book on electro-plating, such as Field and Weill's " Electroplating " :(Pitman, 1946, 15s. net).

Messrs. Canning (address above given) may be ableto supply a suitable " silver meter."

If you have access to a chemical balance, you canobtain an indication of the amount of silver depositedby accurately weighing the object before and afterplating. In this case, the increase in weight willrepresent the quantity of silver deposited.

Sterilising! Air in a LaboratorYTN a small laboratory, size gft. by 6ft. by 8ft. bin:,A used for the preparation of sterile solutions,I wish to institute a system whereby the air in thelaboratory is sterile and maintained at a higherpressure than that outside.

This will entail drawing air from outside thelaboratory through some sort of filter into apump fromwhich it presumably escapes by leaking past thedoor.

What I want to know is :(a) The type of filter necessary.(b) Capacity and type of pump.(c) How many changes of air per hour are

necessary ?(d) How is the air pressure inside and outside

the laboratory measured ?-H. T. Thomas (Kelso).

YOU will require a certain amount of reliableequipment for the establishment and maintenance

of sterile air in your laboratory. It will be necessaryfor you to have a small rotary pump which is caused todraw air through a bin. layer of glass wool ("Fibreglass"),and then through two or three separate " wads " of thismaterial which have been impregnated with a hypo -chlorite solution, such as can be obtained from I.C.I.,Ltd. The " wads " of glass wool should be looselypacked and should be about 3in. thick and 6-8in. square ;all these, of course, being contained in a suitable glassjar fitted with inlet and delivery tubes. The glasswool wads will have to be re -impregnated with thehypochlorite solution every day.

Suitable glass wool can be obtained fairly clieaplyfrom Fibreglass, Ltd., Ravenhead, St. Helens, Lin. cs.

Pumps suitable for the work are obtained from anyof the following firms, although in these days theremay be great delay in delivery of a suitable pump :

Messrs. James Beresford & Sons, Ltd., Cabo StreetWorks, Birmingham, 7.

Watson -Warner Pumps, Ltd., Pottery Lane, New-castie-on-Tyne.

.E2 THE P.M. LIST OF BLUEPRINTS"PRACTICAL MECHANICS" 12 FT. ALL -WOOD CANOE.* New Series. No. I. 3s. 6d."PRACTICAL MECHANICS" 10 -WATT MOTOR. New Series.' No. 2. 3s. 6d."PRACTICAL MECHANICS" COMPRESSED -AIR MODEL AERO ENGINE.* New Series.

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Southampton Street, Strand, W.C.2.= An * denotes that constructional details are available, free, with the blueprint.

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ek.

176 NEWNES PRACTICAL MECHANICS

Messrs. Philip Harris & Co., Ltd., LaboratoryFurnishers, Birmingham.

Hardly more than one complete change of air in theroom every two or three hours will be necessary, butin order to set up a constant slight pressure, the pumpwill have to be a substantial one and all possible leakagesfrom the room will have to be eliminated. The pumpmanufacturers themselves will advise you as to the besttype of pump to establish any required pressure.

For pressure measurements inside and outside theroom, a barometric mercury tube is the simplest and,also, a sensitive means of measurement.

Furniture CreamT WANT to start manufacturing a furniture

cream in a small way.Could you give me a formula for a cream that

only needs to be rubbed on, dries quickly andleaves a brilliant non -greasy hard surface ?-A. Bullock (Beeston).WE note that you wish to prepare a furniture cream,

as distinct from the more usual paste polish.A cream formula is the following :

Canauba wax .. .. 6 parts (by weight)Japan (or candillila) wax .. 31 33.

Paraffin wax ..Turpentine ..White soap ..Pale resin ..

.. 12 ,, 53

3 )3

WaterDissolve the soap in the water. Dissolve first the

resin, then the waxes in the hot turpentine. Allowthe resulting solution to cool so that it is just warm.Then heat the water to nearly boiling -point and add theturpentine solution of the resin and waxes with con-tinual (and preferably mechanical) stirring, whichshould be continued until the resulting cream is quitecold. If the cream is too thick, add more hot water.The cream may be coloured or tinted with a trace ofdye, if required. It may also be perfumed.

Unfortunately, the materials above mentioned areall difficult to obtain unless you are an establishedpolish manufacturer.

Decoration of China Under GlazeT SHOULD be grateful if you could supply meA with detailed Information on the abovesubject, especially on the following points :

(t) Obviously metallic oxides must be used forcolouring. What oxides produce black, grey andother colours ? Can they be obtained ?

(2) What oil medium is used for brushwork,and up to what temperature must the design befired ?

(3) What is the composition of the glaze ?(4) Would you suggest a coke oven blown up to

the required temperature ? Can you advise hod/to construct a simple one ?-C. S. Knapp (Gillingt.ham).

\ METALLIC oxides and other compounds forI) ceramic use are obtainable from Wengers,Ltd., Etruria, Stoke-on-Trent.

Ceramic colours are usually compounded to secretformula. Here, for example, is a published formulafor a black ceramic colour :

Iron chromate .. 24 partsNickel oxide (black) .. 2Tin oxide .. 2Cobalt oxideA dove grey is produced by the following formula :Nickel oxideCobalt oxideChromium oxide : : . xFlint..........IS Paris whiteIn all cases, however, it is better to purchase ceramic

colours ready prepared.(2) Yqu can mix your colours with a little raw linseed

oil, or, better still, use the oil or other medium which isprepared by the colour makers. No standard ratio ofcolour to oil is extant. The colour should just " flow "on the unglazed surface.

The design is fired around 1,100 deg. C. to 1,250 deg.C. for about five hours, depending on the nature of theclay, the glaze and the colour.

The glaze is similarly fired, but for a period up toeight hours.

(3) Glazes vary enormously in composition. Likecolours, they can be purchased ready compounded foruse. The following is a typical formula for a hardglaze :

Feldspar .. .. 25 partsFlintRed lead .. .. 15Plaster of pans .. " I(4) We doubt whether a coke oven furnace would

suit your purpose. A specially designed gas mufflefurnace, or, better still, an electric furnace is reallyrequired. You could construct a simple gas furnaceby arranging a ring of gas jets (blue flame) within anasbestos -lined firebrick chamber, making sure that thegas jets do not actually impinge on the articles beingfired.

You will understand, however, that, within the spaceof a short reply, we cannot give you all the details andinstructions which you are apparently seeking. Hence,we must refer you to a suitable elementary textbookon the subject, such as " The Potter's Craft," by C.F. Binns, or " Handcraft Pottery for Workshop andSchool," by H. and D. Wren. Another book whichwould be of interest and use to you is C. F. Binns'" Manual of Practical Potting."

Lighting and Charging PlantTN the accompanying diagrams Fig. x givesA details of a cut-out attached to a smallgenerator. . Fig. 2 is a charging circuit I havearranged for lighting two lamps and for charginga 12 -volt battery.

Would you please advise me on the followingpoints :

(x) Is the circuit in Fig. 2 correct, especiallyfrom terminal P through the red lamp ?

(2) Would the lamps get full generator voltageif I removed the 12 -volt battery ?

(3) When and how does the cut-out operate ?(4) Would the regulation of the cut-out have

to be altered to run the lights without thebattery ?-J. B. Singleton (Scunthorpe).(T `1 IN order that the red lamp shall light from theI. generator when switched on, the circuit shouldbe from (P) terminal through the lamp and switchto the (-) terminal.

Bucking nr.-Shunt

PointsResistance Dynamo

Fig. 1. Diagram of cut-out

RegulatorPoints

P Red Lamp Switch

Fig. 2.

Head AndRear Light

Switches

Rear And Head"" Lamps

ParallelField

Resistance

Switch

Fuse

Battery

Lighting and charging circuit.-(J. B. Singleton.)

(z) The lamps would receive the full generatorvoltage if the battery was removed.

(3) Apparently the regulator contacts are of thevibrating type, the coil connected to the cut-outcontacts being connected so as to assist the buckingshunt coil when current flows to charge the battery.When the voltage rises high enough the core magnetismis strong enough to close the cut-out contacts so thatcharging current passes to the battery. The currentthrough this coil then assists the bucking coil to increasethe period of opening of the regulator contacts, toavoid overloading the generator when the battery isdischarged, and its voltage low. The battery voltagerises with charging and the charging current will ceasewhen the battery voltage is equal to the dynamo voltage.Should the dynamo voltage fall, due to reduced speed,a reverse current through the cut-out coil will opposethe voltage coil and weaken the core magnetism sothe cut-out will open.

(4) It should not be necessary to alter the regulatorin order to run the lights without the battery, providedthe voltage is correct with the battery also in circuit.

Argon : Tungsten WireTN connection with experimental work I shall beA glad if you can help me with the following

(x) Can you state at what pressure it is usualto fill electric lamps with Argon ?

(2) Is Argon of 98 per cent. purity good enough ?(3) Can you suggest where I might obtain

.001 tungsten filament wire ?-G. Davies (Brook -mans Park).

THE degree of vacuum in a gas -filled lampvaries a good deal. Originally, such lamps

were filled under slight pressure. Now, however, thegas pressure is reduced to about a twentieth of anatmosphere. Pure argon is rarely used, a mixture ofabout two-thirds argon and one of nitrogen beingpreferred.

(2) Argon of 98 per cent. purity may or may not begood enough. It all depends on the purpose of thelamp in question. If the 2 per cent. impurity in your98 per cent. argon is nitrogen and nothing, else, welland good. A minute trace of oxygen is 'mit of muchconsequence, since this will quickly disappear. Butif the impurities embody any water vapour, then thegas is highly unsuitable. The most minute trace ofwater vapour in a lamp gas will steadily deteriorate thefilament, the water vapour traces setting up a cyclic

( I )

February, 1948

action, so that relatively few water vapour moleculescan effect a great damage within a lamp.

If the argon contains traces of the other inert gases-helium, neon, krypton, xenon-no harmful effectswill occur. .

(3) Tungsten wire, of varying thicknesses can beobtained from one or other of the following firms:

Messrs. Johnson, Matthey and Co., Ltd., HattonGarden, London, E.C. ; British Driver Harris Co.,Ltd., Little Peter Street, Manchester, 15 ; Messrs.Everitt and Co., Ltd., 40, Chapel Street, Liverpool:

Waterproofing Indian InkWOULD you please tell me what I must mix

with Indian ink to render it waterproof ?-J. Hunter (Dulwich).0.00D quality Indian ink is usually quite

waterproof after it has been exposed to light andair for a few hours.

Your best plan is to dissolve a single crystal ofpotassium dichromate in a teaspoonful of water and tomix a little of the resulting orange solution with the ink.After being exposed to light for a few hours, this inkmixture will become quite insoluble in water.

You must only treat a small amount of ink at a timewith the bichromate solution, otherwise the whole ofthe ink in the bottle (if exposed to daylight) will becomea thick mass and will not flow well from your pen.

Luminous PaintCOULD you please supply me with the necessary- formula for phosphorescent paints used tocover the figures of dials ?

I have seen paints giving the phosphorescencein three colours : green, pink and blue, and alsophosphorescent enamel covering an ash -traymade from pressed sheet. How should I make it ?

In what books could I find something aboutphosphorescent paints and enamels ?-K. Edwards(Henley-on-Thames).QATISFACTORY luminous paint is very difficult4" stuff to make. In fact, the only really efficientmaterial of this nature is that which contains a traceof radium salt.

However, for the making of an ordinary luminouspaint, proceed according to the following formula :

Calcium oxide (lime) .. .. 5 gramsSulphur toStarch

Heat the above to white heat for 2o minutes. Thisforms the " luminous base," although it is not luminousitself.

To make a luminous powder from the above, usethe formula below :

Luminous base (as above) .. .. 15 gramsPotassium sulphate .. 0.25 gramsSodium sulphate .. 0.25 grams

per cent. solution of bismuth nitrate o.5 c.c.per cent. solution of thorium nitrate t.0 c.c.

Calcine the above at white heat for a quarter of anhour and expose the residue to sunshine. It will havea bluish luminescence.

Unfortunately, however, thorium compounds are notnow obtainable without a special permit, since theyare radioactive. You will, therefore, have to omit thethorium nitrate, but we are afraid that the result willnot be good.

You can obtain luminous (no -radium) powders forpaint -making from Home's Luminous Co., Ltd.,London Road, North Cheam, Surrey.

There is no book dealing comprehensively with themaking of luminous paints. Information is to befound scattered through the back numbers of variouspaint and chemical journals, but, for the most part,the " know how " of this manufacture has been keptmore or less secret..

Waterproof Glue and CementCAN you please supply me with particulars for

making a glue that will fasten hooks on togut for fishing purposes ? Is there a solution orpreparation that I could buy ?-S. Beedham(Sheregreen).AWATERPROOF cement used for the making of

microscopical preparations is made by Messrs.Flatters and Garnett, Ltd., Oxford Road, Manchester,13. This-cost about 2s. per bottle-might suit yourpurpose.

Alternatively, you might use any type of cellulosecement ; or, again, you might use ordinary thick gluesolution in which has been dissolved a little potassiumdichromate, say 3 parts of the dichromate in 97 partsof the glue solution. This dichromated glue mustnor be exposed to daylight, for it possesses the propertyof becoming insoluble under the influence of light.It can be exposed to any ordinary household artificiallighting.

Make the joint with the dichromated glue, let it.set, and then expose it to strong daylight-preferablysunlight-for about half an hour, after which time theglue will have been insolubilised.

PRICE CORRECTIONThe price of S. G. Brown Type "K"

Headphones, as advertised in PRACTICALMECHANICS for. January, page 113, should readPrice £5 : 5 : o per pair.


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The Grasshopper MindYOU know the man with a

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At hoine in the evening he tunesin the wireless-gets tired of it-then glances through a magazine-can't get interested. Finally,unable to concentrate on anything,he either goes to the pictures orfalls asleep in his chair. At theoffice he always takes up the easiestthing first, puts it down when itgets hard, and starts somethingelse. Jumps from one thing toanother all the time.

There are thousands of thesepeople with "Grasshopper Minds"in the world. In fact, they are thevery people who do the world'smost tiresome tasks-and get buta pittance for their work. Theydo the world's clerical work, andthe routine drudgery. Day afterday, year after year-endlessly-they hang on to the jobs that aresmallest -salaried, longest-houred,least interesting, and poorest-futured !What is Holding You Back ?

If you have a " GrasshopperMind " you know that this is true.Even the blazing sun can't burna hole in a piece of tissue paperunless its rays are focused and con-centrated on one spot! A mindthat balks at sticking to one thingfor more than a few minutessurely cannot be depended upOnto get you anywhere in your yearsof life !

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Here is the answer. Take upPelmanism now ! A course ofPelmanism brings out the mind'slatent powers and develops themto the highest point of efficiency.It banishes such weaknesses anddefects as Mind Wandering, In-feriority, and Indecision, and intheir place develops strong, posi-tive, vital qualities such as Opti-mism, Concentration, and Reli-ability, all qualities of the utmostvalue in any walk of life.

The Pelman Course is fullyexplained in The Science ofSuccess. The Course - is simpleand interesting ,and takes up verylittle time. You can enrol on themost convenient terms. Thebook will be sent you, gratis andpost free, on application to -day to :

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Crinothene-Cellulose Acetate-Parch-ment-Plastics-Lampshade Franies andPatterns-Raffia-Plastic Leather-ToysModels-Materials, tools and fittingsfor Crafts that are different.Send 11- for copy of the Magazine

CRAFTWORKER(includes full price lists)

HOMECRAFTS (Dept. 2), AlbionStreet, Broadstairs, Kent.

t;I'sm BATTERIESINERT

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CRYSTALTONE PIEZO CRYSTALPICK-UPS. A brand new crystal pick-up,boxed and unused, for only 3716 ! Full -recorded frequency range covered. Lightweight of pick-up on record practicallyeliminates wear and surface hiss.

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ADMIRALTY RECTIFIER UNITS,1204B. A fully stabilised and smoothedpower pack for use on 230v. A.C. withoutput of 500v. at 170 m,,A. Weight 60Ibs.Incorporates rectifying valve and twostabilising valves. Only £21151-. (Carriageand packing 10/-.)

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A CARBON PILE VOLTAGEREGULATOR, complete with seleniumrectifier and rheostat. Only 51-. (Carriageand packing II-.) New and unused.

HAND GENERATORS. A new andunused 10 -watt hand generator, of U.S.A.manufacture, complete with winding handleand connecting cable. Specification : 162v.,.06 amps and 3.1v., .3 amps. 60 RPM. 30)-.(Carriage and packing, 116.)

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ir178 NEWNES PRACTICAL MECHANICS

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2.0 hy., 120 mla., 1016 each ; 30 hy., 150

rill,. 2216 each.MAINS TRANSFORMERS, 230 volts.50 cys. I ph. input. Output 500101500 voltsat 250 mla., 5 v. 3 a., 4716 each. Anotherwith two windings of 61- volts 5 amps.,301- each ; another with 350101350 v.,180 mla., twice three 6.3 volt windings andtwo 5 volt windings, 4216 each ; another50 volts at approx. 50 amps., also a 5 voltwinding, 231151-, each CIF. All the aboveTransformers are very large type, so pleaseallow 316 for carriage.EX-R.A.F. ELECTRIC FANS ORBLOWERS, 12 volts A.C. or D.C.,complete with Sin. impeller, brand new,boxed, 271- each ; current taken at 12 volts3.2 amps.T.C.C. CONDENSERS (New). 4 mf.1,000 volt working, 316 each. PIF MainsSmoothing Chokes (New), 10 hy. 150 mfa180 ohm, 816 each. Ditto, 10 hy. 80 ma -200 ohms, 616 each.EX-R.A.F. D.C. TO A.C. ROTARYCONVERTORS, 12 volts D.C. input,220 volts 50 cys. I ph. at 100 watts output,851- each.MAINS VARIABLE RESISTANCES,worm wheeled controlled, 5.7 ohms 8 amps.,351- each ; ditto, 60 ohms 1.5 amps., 301 -each ; both new and unused.SHUNT WOUND D.C. 110 voltmotors, 1,500 r.p.m. approx. h.p., con-dition as new, 1716 each, post 21..'-X-GOVT. NEW MAINS TRANS-ilORMERS. Input 200/250 volts, Output525101525 v. 150 mla, 5 v. 3 a., 6.3 v. S a.,351- each, post 216. Special price for lots ofhalf dozen or more.

LEARNTO

EARNLeave the overcrowded ranks of the poorly paid-' letThe Bennett College help you to the top where there isalways plenty of room for the well -trained. Just chooseyour career or let us advise you. The Bennett Collegewith its proud tradition of friendly persarial tuitionand its long record of triumphs, is the most progressive,most successful Correspondence College in the World.We teach nearly all the Trades and Professions by postall over the Globe. DISTANCE MAKES NODIFFERENCE.

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requirements above, write to us onany subject. Full particulars free.

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74 College with a as well as brains

February, 1948

ELECTRADIX BARGAINS.TRANSFORMERS, double wound formodels, etc., 230120 volts 2 amps, 301- ;

230/12 volts 3 amps, 3216.Auto Transformers, 2301110 volts 85watts, 351- ; 300 watts, 651- ; I k.w.,571101-.

CRYSTAL SET. TheLesdix Bijou Crystal setin bakelite case, semi -perm. detector, con-denser tuning, 151-.Headphones, 2216 pair,with cords.

BUTTON MICRO-PHONES provideinteresting e x p e rments for making out-side listeners, soundtransmission, etc.These ex-G.P.O. VoiceUnits are under lin.diam., filled carbon ""'"),granules and fittedmica diaphragm, 316 each. Special Trans-former and Condenser, 51-. InstructionLeaflet with each Button. G.P.O. Mikeinserts, 216.HAND MIKES in moulded bakelitecase, 416. Tannoy hand mike, multi -cellcarbon type, metal case with neat switchin handle, 1216, special transformer, 816.SEND -RECEIVE Hand -corns. All -metalfield type ; the famous No. 16, Govern-ment pattern, as used in field telephones ;mike and ear piece with damaged switchin handle, 51- each. Double Headphonecords, 216. 4 -way 5 -foot cords, ex-G.P.O.,216.MAGNETS. D.C. Electric magnets,weight 113oz., lift on 2 volts, 111b., 4 volts31b., 6 volts 41b., new, surplus, 716 each.Permanent powerful flat bar magnets,2in. x lin. x Ain., drilled 2 holes eachend, for any pole pieces, 21- pair. Thewonder Midget magnets. Alni perm. steeldisc. ; 'in. diam., in. thick, with 3116in.centre 'hole, 316 each. Large stock ofHorseshoe magnets. Send for specialMagnet Leaflet " P.M."

Please include postage for mail orders.

ELECTRADIX RADIOS214, Queenstown Road, London, S.W.8

(Late Queens Road)Telephone MACaulay 2159 -

Higher andHigher

stands the reputation ofHarbutt's " Plasticine." Formore than fifty years it hasbeen the only reliable materialfor model makers of all ages.Whether for home amusement- designing - experimenting-or the handyman, " Plasti-cine " is indispensable. Be-cause it is ever -plastic andhygienic, " Plasticine " hashundreds of other uses, and it

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'Plasticine'HARBUTT'S PLASTICINE LTD.,BATH AMPTON, SOMERSET.

LONDON : 68, Victoria Street, S. W. t.

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ELECTRIC MOTORS2A v. D.C. for driving models of alldescriptions, and -cameras. Can beadapted for many useful experimentalPurposes. All brand new. Price 15/ -each.

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STEEL TAPEMarked in metres. 50 metres long.On reel and winder ; for builders.surveyors and all purposes requiringmeasurements of land and floorspace. 50/- each.

POCKET SAWOf high speed steel. When extended42ins. long. Complete with sharpeningfile and tooth bender. Price 10/- each.ORDNANCE MAP CASECelluloid window -Mins. x 181ns. ZIP -fastening, laminated cloth roll, 25/-.

SPRINGBALANCE WEIGHER

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No C.O.D. Delivery 8 to 10 days. Fullmoney back guarantee.

M. LAWTON, (Dept. P.M.)

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ATTENTION! PLEASESets of CLEAR DIAGRAMS' and IN-STRUCTIONS for making easily fromreadily obtainable materials only.

1. Toy and Model Maker's Lathe 3/62. Toy and Table Model FretJig Saw Machine 3/6

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6. Tubular Furniture (all kinds) 2/67. High Tension Batteries 3/6

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LAE:ORATORY APPARATUSAND CHEMICALS.

Send today for New Lists and OrderForm. 2d. Stamps.

A suggested order for the StudentBeginner :-1 Flask 150 ml. 1/10. 1 Beaker 100 ml..

1/8.1 Gas Jar (with plate). bin. x L in., 2/Old.1 Beehive Shelves, 3in. diam., 1/3.1 doz. Test Tubes, 51n. x lin., 1/4.1 doz. Corks for above, 5d.1 Tripod Stand, Collapsible, 1/6.1 Wire Gauze Plain, 5in. x 5in., 8d.1 Bunsen Burner, Student's, 2/,1 doz. Tubes Assorted Chemicals, 4/6.

£1, inc. Post and Packing.Easy Home Chemistry Book for Boys,2/-. Post 4(1.

ELECTROTORS.290. 8/6, post 4d. 242. 10/6, post 9d.

List S.A.E.

TRADE ALSO SUPPLIED.

VICSONS & CO.,148, PINNER ROAD,

HARROW, MIDDLESEX.

SOldIers. Aeroplanes.Farin-and Wild

Casting moulds deepcut Patti

Animals. Can. meStamped envelopefor list. IllustratedCatalogue 6d

POST RADIO SUPPLIESRemote Contactor. New, with manyuseful items including luminous dialand pointer. 3 amp. toggle switch, tworelay bobbins wound 3 ozs. clean enam-elled copper wire, two Platinum con-tacts. cable leads, etc., 3/6 each. 3different Multi -point Switches, silvercontacts. 3 for 2/-, 7/6 doz. 10 -wayTerminal block and connector.30 screws,1/- each. 6 for 5/-. Hamoill heat -resist-ing rubber cover copper connectingwire. 12 yds. 2/-. Peribraid sleeving,finest quality. high voltage, variousColours, 1 M.M., 1.5 m.m., 4d. yard.Bakelite bobbin wound 1/ ozs. cleanusable 36 s.w.g. enamelled copper wire.1/- each, 10/8 dozen. Used ex-R.A.F.low resistance earphone with switch,2'6. New S.G. Brown ex -Army highresistance headphones, complete withheadband and leads, 12/6 per pair.New U.S.A. single small earphone,1,000 ohms resistance. 5/8. New U.S.A.high resistance headphones, completewith headband and lead, 12/6 per pair.As above, but special lightweight withdetachable rubber ear guards. Com-plete. 15/- per pair. All above postageextra.Send S.A.E. for list of insulated copperwires, screws, nuts, tags, Ebonite andlaminated Bakelite panels, coil formers,etc., etc.

POST RADIO SUPPLIES33, Bourne Gardens, London, E.4.

A Fine SetThe verdict of many satisfied con-structors using the famous DORSETCircuits.NOVICE or EXPERT. These circuitsare TOPS. Each manuscript containsvery detailed instructions, easy to readblack and white drawings, point toPoint wiring, every step and stagedescribed. - NO RADIO EXPERI-ENCE necessary.

DORSET 2/6 CIRCUITSeach

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DORSET COMPONENTSspecially designed for above.

Chassis. Coil packs, Group Boards,I.F. Transformers, Chokes, MainsTransformers, Speakers, etc.

Hot Spot " battery soldering Outfits.Send Id. for list. Theoretical circuits,

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WELDONARADIO ACCESSORIES LTD.38. Gloucester Road, BRIGHTON.

TOY -CASTING MOULDS-DEEP' CUT

Soldiers, sailors, airmen, ships,'planes, tanks, cars, fkrm animals,wild animals and keepers. Samplemould 3/6. Plastercraft MetalMoulds. -Wall plaques, galleons,brooches, dog ornaments, etc.Sample mould of brooch 3/6.German flat moulds from 3/6.S.A.E. for List. 6d. for IllustratedCatalogue.NUTHALL, 69, ST. MARK'S RD.,

HANWELL, LONDON, W.T

ELECTRIC ENGRAVERS. -Powerfulinstruments in cylindrical case, onstand with spring attachment andswitch. Suitable for dog collars, toolmarking, etc., 4-6 volt model, price50/- A.C. Mains model. 200-240 volts,60/- : A.C. Engraver only 50/,TELEPHONE SETS, comprising 2G.P.O. hand phones. 2 bells, 2 pushesand 80ft. twin wire. Price 65/, postfree. Single instrument, 25/8.6 inch Brass Brackets lin. thread, 1/9.S.B.C. Fancy glass shades 1/9. Circularresistances on china base 10 ohm.. 2/-.Screwplates for threading 0 2 4 B.A. 4/8.MOTOR. -4-6v. dry battery driven,well made, powerful. 11/8. Illustratedlist, 6d. Carbon Diaphragm1/- each and carbon granules64. packet.BATTERY CHARGERS FOR A.C,MAINS. FOR CHARGING 2 -volt accu-mulators at 1 amp. Parts with diagram,12/8. Complete 21/6: Postage 10.1.FOR TRICKLE _CHARGING CARCELLS, parts with diagram. Output11 amps. for 6v.. cells, 30/- set. For12v. cells, 35/- set.Larger sizes quoted for.MINIATURE HEAD-PHONE. Reproducesequal to best 'phones.Fits into ear, does notrequire headband. Twonipples large and small10 ohm or 1,000 ohm.Black or flesh en-amelled. 9ft. cord.Price 301-.ECONOMIC ELECTRIC CO.,64, London Road, Twickenham,Middlesex. Tel.: POPesgrove 1318

MODEL ENGINEERSFOR THE TURNER:

Lathes, 31 and 4} S.S. Bench Millers. Drilling Machines.Hand Bench Shaping Machines.

FOR THE WOODWORKER :Wood Turning Lathes, 21- and 51" centres. 4in. Planers. Saw

Benches. Sanders. Spindle Moulders.

Pedestal Jig and Fret Saws.

Per,spen,-- All sizes and colours in stock.

MUTTALL'S (LATHES) LIMITED,MANSFIELD, NOTTS.

Our latest Model isa REAL RADIORECEIVER, whichIs fitted with aPERMANENTCRYSTALDETECTOR.WHY NOT HAVEA SET IN YOUROWN ROOM ORAS A STAND-BY I-9/6, post 66.nE LUXE RE-CEIVER in poi.shed oak cabinet.18/6, post 1/-.

Spare Permanent Detectors, 2/- each. When or-dered separately, 2/6. Postage, N..0003 Pre-set Condensers, 2/, post 3d. Headphones,brand new, S. G. Brown, G.E.C., etc., 15/-, 23/-,and super -sensitive, 30/. a pair, postage 66.

HIGHSTONE UTILITIESCRYSTAL SETS

MICROPHONESJust the thing for impromptu concerts, room toroom communication, etc. Bakelite table model,6/9; Suspension tope, 8/8, Post 66. Super Modelon stand, 12/6. Fitting Instructions included.Mike Buttons, 2/6. Transformers, IV-. PublicAddress Transverse current Mike, 37/6, post 1'-.All microphones have transformer incorporated.

MORSE. KEYS AND BUZZERSStandard size keys wired to work Buzzer or Lamp.Chromium plated, 7/6. No. 3 Heavy Duty DoubleCoil, 4/9, post ad, Plugs (for Jacks) with shortlength of twin flex, 1/6, post 4d.

BELL TRANSFORMERSThese guaranteed trans-formers work from any

;A.C. MAIM giving 3, 5,or 8 volts output at 1amp., operate bulb,buzzer or bell. Will

supply light in bedroom orlarder, etc. PRICE 7/-. Post 86'BELLS for use with either the

above or batteries, 11/-, Post 6d,

SOLDERING IRONSAdjustable Bit, all parts replaceable and fullyguaranteed. 200/250 v., 60 watts, 8/6 ; 150 watts.121, poet 86. Small Soldering Irons, for useon gas, 1/4. Post 4d. Resin cored solder for easysoldering, 8d. packets, or Ilb. reels, 6/-. Postageextra.

Sparking Plug Neon Teeters with vestpocket clip, 2/6, post 3d.

Ex-R.A.F. 2 -valve (2 -volt) MicrophoneAmplifiers as used in plane inter -corn.,in self-contained metal case, which Inturn is housed in a useful wooden box,10,- each (less valves), post 1/-.

Wield. Intercommunication Sets, ready foruse, complete with ringing hand generator,bell, signal lamp, morse key, relay andall necessary jacks and switches. Con-tained in a strong metal ease with circuit,diagram. 25/- each, carr. 2/6 ; 47/6pair, carr. 2/6. Telephone hand generator,with handle, 9/6, post 1/6. Bell, 4/6, post 6d.

Hand Microphones, with switch in handle,and lead, 4/-, post Bt.

' Headphones, reconditioned and in goodorder, 5/6 a pair, post 6d. (better quality,7/6 pair). These phones and mikes canbe used with telephone sets above.

New Headphones, 10/- a pair, post 6d.Balanced armature type (very sensitive,open bracket and suitable for use withcrystal sets), 15/- a pair, post 6d. NewSingle Earpieces, 3/6. Bal. armature type,6/-, post 4d. Headphone cords, 1/- a pair,post 3d. ( S4 per 100). Replacementbands for headphones, 1/ -,post 4d. (14per 100). Wire bands, 6 per pair ( 42per 100). Rotary Transformers, 12 v.D.C. input, in sound -proof cabinet, forCar Radio, etc., will also light two 25 w.lamps in series, 22/6 each, carr. 2/6.

Rola Bin. P.M. Loudspeaker and cabinetwith volume control, $1, post 1/6.

METERS, COO m,a., 3in., m/c., 15/-;Double rending 40/120 rn/a., 2in., rn/c.,11/- ; 20 amp., 2iin., mid, 7/6 ; 15 volt,2iin., rn/c., 9/6 ; 30 amp., Gin., m/I Switch-board mounting, 35/- ; 120 volt 81n.,rn/i switchboard mounting, 37/6 ; 6,000 v.3iin., m/c., 43/10/-. All postage extra.SEND 1d. S.A.E. FOR ILLUSTRATEDLIST B.P. OF USEFUL ELECTRICALACCESSORIES. Money refunded if notcompletely satisfied. Letters only. Pleaseinclude postage ; any excess will berefunded.

HIGHSTONE UTILITIES58, New Wanstead, London,

E.I I

0


THE NEW

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The NEW much -improved Philidyne Lighting Set hasrapidly established itself as an outstanding success with

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The NEW 8 -Pole Dynamo (type 7422) weighs only9i ounces yetis rated at 6 volts, .5 amps. Very smoothin action. Self-lubricating. Polished aluminium finish.

The NEW Headlamp is streamlined, with black lacquerfinish, chrome -plated rim and polished reflector.

Designed to take a flat battery for parking or traffichalts. Switch on top of headlamp gives siinultaneousconnection to either Dynamo or Battery.

The NEW, Rearlamp gives improved access to thebulb -holder. Lens is of heavy plastic, prismedinternally with smooth convex exterior.

PRICE complete with twin -flex cable and clips 43/6d.

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BRANCHES AND SALES DEPOTS AT BIRMINGHAM, BLACKBURN, BRISTOL, CARD&F, EDINBURGH, GLASGOW, LEEDS, LIVERPOOL, MANCHESTER, NEWCASTLE, NOTTINGHAM, SHEFFIELD(PH.3 I 3B)

DITNLO \AO,

JUBILEE 1888.1948,Zeeede

8 Hi 31.3

February, 1948 THE CYCLIST 33

VOL. XVI

c541( -

Editor : F. J. CAMM

FEBRUARY, 1948 No. 311

Comments of the Month

All letters should be addressed tothe Editor, " THE CYCLIST,"George Newnes, Ltd., Tower House,Southampton Street, Strand, London,

W.C.2.Phone : Temple Bar 4363

Telegrams : Newnes, Rand, London

Cycle Show in NovemberFOR the first time since 1938 The Cycle

and Motor Show is to be held atEarls Court from November t8th to

the 24th. This is good news indeed, for itindicates that the industry is back again onits feet. Although supplies to the publicwill still be scarce the show presages a time,not far distant, let us hope; when all controlswill be removed and cyclists will be able topurchase in a free market, with a free choice ;when there will be an abundance of goods andour exports consist cf an over -spilling in theforeign markets of production in excess ofhome needs.

The cycle industry was one of the first toget back to its peacetime activities, and thevigilance of the British Cycle and MotorCycle Manufacturers and Traders Unionhas been responsible for the removal of manyof the restrictive controls.

Steel and other raw materials used in themanufacture of bicycles and accessoriesremain a handicap supplies.Notwithstanding this the industry is produc-ing goods at a rate almost equal to the pre-war level. Many countries have for the firsttime sampled the delights of British bicycles,and even America, whose bicycles look likethe grandparents of all dreadnoughts, isbeginning to either purchase British bicyclesor the American copies of them, instead ofthe imitation motor cycles with dummy tankswhich provide film stars and others with ameans of getting their photographs into thepapers.

Cyclists have enjoyed a greater freedomfrom controls and restrictive legislation thanother road users, for successive Governmentsnaturally hesitate to offend so large a votingsection of the population. It istrue that onthe question of rear lights and one or twoother small matters points have had to beconceded, but in the main we retain ourfreedom.

At the Show there will be reunions andcelebrations. We shall meet old friends whomwe have not seen for over 8 years. We shallsee under one roof all of the new bicycles andaccessories, and be able to survey the wholeindustry from one building. Clubs will includea visit to the show as an item in their clubrun calendar.

Let us hope that no international catas-trophe causes the plans to be abandoned orthat some internal crisis does not do so as itdid last year. The industry is ready to'exhibit its goods to its home market and itsforeign buyers.

Battery LampsTHERE has been much criticism regarding

the quality of battery lamps, which inthe opinion of cyclists are cheap and shoddy.It has been suggested that a big marketexists for a reliable combination of front andrear battery lamps. In defence of the batterymanufacturers we should like to say that thelimitation of supplies and the poor quality

of the materials available are responsible formost of the causes cf complaints.

The, zinc pots used in dry cells is of alighter gauge and therefore not so durable.This is not the fault of the manufacturer's ;they are allowed so much metal and have todo their best to make as many batteries aspossible from it. This does give -everyone achance to buy a battery. Like clothing orfurniture or any other article produced to -dayon a utility basis, quality has to suffer be-cause of the shortage of material. We do notthink that the criticism of batteries is reason-able at the present time.

The Committee on Road SafetyTHE Minister of Transport, as previously

recorded, has set up a Committee onRoad Safety as a permanent feature of theorganisation of the Ministry in relation to thestudy and prevention of road accidents. Thesetting up of the committee was recommendedby the Committee on Road Safety whichrecently issued its final report after threeyears of intensive survey of the road acci-dent problem.

The new committee will be presided overby Mr. James Callaghan, M.P., Parliament-ary Secretary to the Ministry of Transport,and it is composed of members nominatedby the government departments concerned,the police, education and local authorities,road users' associations, the Royal Society forthe Prevention of Accidents and the TradesUnion Congress. The committee will advisethe Minister on those matters relating to roadsafety which he may refer to them, and willreport to them on other questions which seemto be of importance to the relation of roadaccidents.

The members of the Committee are asfollow: Mr. H. R, Lintern (Ministry ofTransport) ; Mr. E. B. Hugh -Jones, M.C.,B.Sc., M.Inst.C.E. (Highways (Traffic andSafety) and Engineering Divisions) ; Mr. F.G. Humphrey, O.B.E. (Information Divi-sion) ; Mr. J. H. Burrell (Home Office) ; Mr:D. H. Leadbetter (Ministry of Education) ;Dr. W. H. Glanville, C.B.E. (Department ofScientific and Industrial Research) ; Mr. H.G. Whiles (Scottish Home Department) ; Mr.H. Dalton, C.B.E. (Metropolitan Police) ;Capt. Sir Archibald Horden, C.B.E., A.F.C.(English County Police) ; Mr. A. C. West,O.B.E. (English City and Borough Police) ;Mr. J. McConnach (Scottish Police) ; Mr. A.Floyd, C.B.E., M.Inst.C.E. (County Coun-cils' Association) ; Alderman T. J. W.Templeman (Association of Municipal Cor-porations) ; Mr. F. L. Snow, J.P. (UrbanDistrict Councils' Association) ; Bailie PeterMeldrum (Association of County Councils inScotland, Convention of Royal Burghs andCounties of Cities' Association) ; Mr. H. M.Spink, M.C., M.A., B.Sc. (Association ofEducation Committees) ; Mr. J. R. HowardRoberts, B.C.E. ; Dr. Ewart Smart, M.C.,M.A.B.Sc. ; J. A. A. Pickard, D.S.0:

By F. J. C.

(Royal Society for the Prevention of Acci-dents) ; Major R. A. B. Smith (National RoadTransport Federation) ; Major Frank Bale(Standing Joint Committee of the RoyalAutomobile Club, Automobile Associationand Royal Scottish Automobile Club) ; Mr.R. C. Shaw (Cyclists' Touring Club) ; Mr.V. H. Robins (British Motor Cycle Associa-tion) ; Mr. T. C. Foley (Pedestrians' Asso-ciation) ; Miss F. Hancock, Mr. F. Donlon(Trades Union Congress) ; Mr. Ben Hall(Municipal Passenger Transport Associationand Public Transport Association) ; andS. G. Griffin (Secretary).

All correspondence should be addressed tothe latter at the Ministry of Transport, Berke-ley Square House, W.I.

The Committee seems comprehensive, andwe are hopeful that something useful willemerge from it.

Whether or no they implement the recom-mendations made in the Report, which is theraison d'etre of the Committee's existence,remains to be seen. We do not think that allof those recommendations will be adopted.

Nationalised TransportAT midnight on December 31st, 1947, the

principal railways of Great Britain,London Transport, and the greater part ofthe Canal system passed into public owner-ship. The Ministry of Transport alreadycontrols all of the arterial roads of this coun-try and thus is in complete charge of ourroads, the vehicles which use them, as wellas the railways and the canals.

There should be no excuse therefore infuture for inefficiency in our transportsystem, nor for bad roads or bad streetlighting. Fortunately, cyclists are not affectedby this great change -over from private enter-prise to State Control. They are not tied totimetables or queues, and run their owntransport system, which never can benationalised. There are those who watchtheir interests in and out of Parliament. Hasnot the time arrived, however, when a newcycling organisation is required more inkeeping with the times, less hidebound bythe traditions of the past and with more up-to-date knowledge of the changing times ?We have made this suggestion on more thanone occasion, and the time seems ripe torevive it. What is required is an organisa-tion representative only of cyclists' interests,and not especially interested in .touring ortrack racing or time trials. We have anational Committee on Cycling, but its mem-bers are chiefly drawn from existing organi-sations, including the Manufacturers' Union.Their views are well known, and, under-standably, they represent the views of theorganisations to which they are attached.What is required is an organisation inde-pendent of all these bodies and drawing itsmembership from that vast body of cyclistsoutside the comparatively small ranks of thepresent organisation.

a

34 THE CYCLIST February, 1948

Para fains

trera^r....

lititacie 1.Cornwall

The quaint Pod- Office

Smells of Prejudice !COMPLAIN'FS were made at the November meeting

of Grimsby Highways Committee that while scoresof cyclists are regularly fined for disregarding a diver-sion sign in Scarthoe Road, Grimsby, practically everyCorporation bus driver ignores the sign and gets awaywith it. It was described as " making a mockery ofthe law." One councillor said he left the Bench indisgust when one cyclist pleaded guilty, after othershad pleaded not guilty, and was fined double. Thediversion of traffic is. to continue for a further threemonths, so no doubt quite a few more cyclists will beappearing before Grimsby Bench.

Training Them YoungBELIEVING in practical training for children in

road safety, the Parks Committee of Oldham(Lanes) Borough Council has decided to use a portionof their parks as training grounds for child cyclists.The Committee have in mind the construction ofminiature roads and a portion of a town on some fouracres of ground. The children will learn traffic senseand the rules of road safety by ridingtheir cycles andpedal cars while others act as pedestrians. Speciallectures will be given by police experts.

Doncaster's Alderman -cyclistTHE abolition of the basic petrol ration is no worry

to Alderman Walter Crookes, of Doncaster, whohas just completed his twenty-ninth year as a member ofthe town council. The bicycle is his favourite means oftransport and he ought to know as he first startedriding a " penny-farthing " in the very early days of thesport, and was a member of what was probably one of thevery first cycling clubs in the district, the Adult SchoolCycling Club of Doncaster. He is still on the roadregularly, although he celebrated his seventy-seventhbirthday on Christmas Eve. For many years Mrs.Crookes used to accompany him on his trips, but latelyher health has prevented her from doing so.

Cycling at 52 m.p.h.AT Grantham Road Club's roller contest, held in a

local dance hall, the winner of both the 440 and the88o yards sprints was R. Meadwell, of Melton Mowbray,who is the East Midlands Clarion champion rider and alikely competitor in the Olympic Games. His speedin the 44o yards was 52.94 miles an hour. The winnerof the women's 44o yards scratch was Miss G. Copeland,of Oldham Clarion Club, whose speed was 42 miles anhour.

Bedford Trader DiesMR. ARTHUR WILLIAM CHATTELL, of t97,

London Road, Bedford, a cycle trader in thetown for some 25 years, has died at the age of 68.When he first went to Bedford he commenced businessin Ampthill Road, later removing to St. Mary's Street.In 1935 he extended his business and opened an up-to-date shop at the present premises in St. John's Street.Mr. Chattell was a prominent member of the localChamber of Trade, of which he was, this year, vice-president.

Growing UpTHE report of the Fenland Clarion Cycling and

A Athletic Club, presented at the club's first annualmeeting at Peterborough, showed satisfactory progressduring the year. Members agreed that the comingyear would be even more successful. At the meetingMr. P. Goodale was elected chairman and Mr. J. R.Maxfield was re-elected secretary and treasurer.

Police " Lit Up "WHEN an electricity cut in Peterborough after

dark put the traffic lights out of action the lightswere replaced with illuminated policemen. Thepolicemen each wore white helmets, bearing the word" Police " illuminated from a pocket battery, and white

capes, and controlled thetraffic by means of one redand one green cycle lampin the hands. 'f'hescheme, devised by the Chief Constable (Mr. F.G. Markin) when he wasat Salford during the war,worked perfectly, and ateach of the three busycrossings where thepolicemen substituted forthe traffic lights the trafficflowed well without a

check. The three outfitsused by the policemencost altogether t6s.and the Chief Constablehas sufficient material leftto complete a fourth outfit.

End of CavendishBridge

THE last remaining archof the Cavendish

Bridge, which spannedthe River Trent atShardlow for t76 yearsuntil it was severelydamaged by the floodsof early 1947, has beenblown up. Blasting

charges were used in the demolition, but these had tobe placed with great care.- as the masonry to beremoved was very close to the Bailey bridge whichwas erected to provide an alternative means ofcrossing the river. The work of demolishing thebridge has taken some five months and a great dealof careful planning.

Delivery Boys' Reliability TrialUOR the first time since the war a post office boyA failed to gain first place in the delivery boys'reliability trial held at Leicester. This year the winningcyclist was 14 -year -old D. Naylor, an employee of theLeicester Co-operative Society. There were 32 entrants,not quite so many as the previous year, but interest waskeen. The boys had 69 minutes to cover a courseof t t J miles in the city, passing five checking pointsand riding so as to observe the rules of the road ratherthan to complete the course in the quickest possible

'time. Cycles were all checked before the start androadworthiness and general condition of the machineswere taken into consideration. The trophy, the RussellCup, is presented by Mr. S. Hibbert Russell, chairmanof Leicester and County Accident Prevention Council.

Finding the TroubleMUDDY, dishevelled and looking a bit under

the weather, an airman called in at a villagepublic house in Huntingdonshire to inquire if therewere anyone about who could have a look at his bicycleand tell him why it was he kept falling off every time hetried to ride. He said it was also making a queer noise.Several Good Samaritans went outside to look at thecycle and were soon able to explain to the airman thata cycle with the handlebars and front wheel bentcompletely round back to front is not the most satis-factory of mounts.

Long-distance Cyclist DiesMR. TOM MADDEX, of Kempston, Bedfordshire,

who recently died, was particularly well knownfor his long distance cycle rides. He won the NorthRoad 12 -hour race in i93o, over a distance of 2131miles, and in 1928, 1930 and 1931 he did 24 -hour ridesover distances of 3951, 383J and 3791 miles respectively.Riding a tricycle, he set up a national record for coveringthe 383 miles from Edinburgh to London in the timeof 27 hrs. 17 mins. He was a member of the Bedford-shire Road Cycling Club, and a life member of theNorth Road Cycling Club, which he joined in 1928.Mr. Maddex was also interested in cycling journalism,being from 1941 to t944 editor of The North RoadGazette.

Cowboy's Ambition-To CycleBACK home for a holiday with his father at Fishtoft,

Lines, is a real live cowboy, " Tex " Bedford.who for .27 years has been riding the ranges in theStates, the Argentine, Canada and Old and NewMexico. Before he goes back home to his ranch inBritish Columbi,a next February he is determined tolearn to cycle. He can do anything on and with ahorse, but a bicycle has so far proved his master.His sister is taking him in hand and when lie goes backshe means him to he a real cyclist. Tex, who is 46years old, has during his cowboy life broken all hisribs but two at one time or another, and if learningto cycle is any tougher than that he will be surprised.

What's Wrong ?LABELLED " What is wrong with this bike ? " a

much ill-treated bicycle was suspended from theceiling in the room in Gallowtree-gate, Leicester,devoted to the Leicester and County ,Safety FirstWeek Exhibition. Judging from the appearance ofthe machine, the boys and girls under r8 who wereeligible for the competition would have found it easierto write down the one or two things that were rightwith the machine. Some ruthless hand had beenso busy with the cycle that anyone who took it on theroad would have been well advised first to book aspace for himself in the local cemetery. Even so,

it was probably only a little more decrepit than somemachines that are actually ridden.

Yorkshire OfficialsMR. FRANK SPENCER, of Blaxton, Yorks, has

been re-elected chairman of the North MidlandsDistrict of the Road Time Trials Council at a meetingheld at Rotherham. On the committee are N. Phillips(Thorne Paragon Club), T. R. Snowdon (DoncasterWheelers), W. H. Lindley (Brodsworth Road Club)and M. Clark (Bircotes).

Prejudiced ?AFTER paying tributes to three L.N.E.R. goods

van drivers at March, Cambs, on the occasion oftheir being presented with awards from the RoyalSociety for the Prevention of Accidents, the chairmanof the Urban District Council said that the great 'trouble of the drivers on the road was cyclists. Sucha sweeping statement. suggesting that every cycliston the road is just a menace to everyone else, oughtto have some foundation in fact before being made.

Generous GiversQ PEAKING at the annual dinner of the Grimsby

Cyclists' Club, held at the Town Hall, Grimsby.the Mayor (Aid. J. W. Lancaster) congratulated clubmembers on their work for charitable causes. Duringthe -seven years since 1940 the club has given altogetherZ:3,690 to various deserving causes and the Mayorsaid it must be a record for all clubs and organisationsin the town. " The public of Grimsby," he said," should be grateful for all the cyclists' club hasdone." Over zoo members and friends were presentat the dinner and the dance which followed.

Fast Married Men !PROBABLY because married men have to be more

nippy on their feet than single men, a 25 mile trialevent organised by Peterborough Cycling Club resultedin a win by the married men's team ovbr the singlemen's team. The aggregate time of the married teamwas 3 hrs. 29 mins. 46 secs. and that of the unmarriedwas 3 hrs. 31 mins. This event was the club's lastevent of the season.

Sensible AdviceTHE suggestion that the State generally is tending

too much in the direction of spoonfeeding peoplewas made by Mr. John Garrett, headmaster of BristolGrammar School, at the School Speech Day, and hegave as one example the fact that the police and othershave to inspect the cycles used by school -children,otherwise the parents would allow children to ridemachines that are in a shocking Condition. " I suggestit is within the province of every responsible father todo that for his children," he remarked. " Unfortunately,however, most fathers seem to prefer to leave the jobto someone else these days."

Not One Of ThoseACYCLIST'who appeared before Peterborough

magistrates charged with ignoring a "Halt" sign, saidhe took exception to the remarks of a policeman whostopped him. He said he had been up and down theroad 15 times that morning and had seen the policewatching, and when he passed the sign he was"dreaming." When he told the policeman he had nooccupation, being in fact a disabled soldier, he saidthe policeman smiled and said " Oh ! You're one ofthose ! "

Tributes to St. Neots ClubMANY tributes to the keenness of members and the

efficiency of the club were paid at the lothannual dinner and prize distribution of the St. Neotsand District Cycling Club, held at the Cross Keys,St. Neots, Hunts. St. Neots was described as " thehome of cycling " by Mr. Woodbine Haylock, presidentof the Bedfordshire Road Cycling Club, and he addedthat the Cross Keys was the Mecca of road racing men.In the chair at the gathering was Mr. E. J. Bass, himselfonce a very well-known figure in road racing circles,who was a member of a cycling club at St. Neots in1896, and he presented the awards obtained during thepast season.

Missing Bicycle MysteryTHE fact that no trace of a cycle could be found

after the body of a man wearing cycle clips hadbeen taken from the water at the North Bank, Thorney,near Peterborough, made the Thorney coroner adjournthe inquest. However, in spite of an intensive searchby the police, no trace of the machine has been foundand at the resumed inquest a verdict of " FoundDrowned " was returned. The coroner said there wasno evidence to show how the man got into the water,where apparently the body had been for several days.

Feet v. WheelsIN the first cross-country scramble between cyclists

and harriers organised by the Boston Cycling^ andAthletic Club over. a 31 mile course the runners werewell ahead of the cyclists. The first six runners hadcrossed the finishing line before the third cyclist hadcompleted the course, but the cyclists secured secondand third places, with a runner first and fourth. A gateand one or two ploughed fields hindered the cyclistsmore than the runners but matters became more evenat other places on the course. One cyclist retired witha puncture during the scramble, and four others foundsimilar pleasant surprises when they had completedthe course.


Around the Wheelworld

"Motives Behind Massed Racing"THE talk by Jimmy Kain as the guest

speaker at a recent meeting of a club,during which he dealt with the history andmethods of the B.L.R.C., and of massedstart racing, has invoked an article in acontemporary under the above title.

The article is written by G. H. S., whoadmits that massed start racing on publicroads is a " subject of more than ordinaryinterest." Kain explained the organisationof massed start events, how law and order onthe..highway is " preserved," how the eventsare marshalled and supervised, and howpolice and other co-operation is secured.

G. H. S., however, thought that theaudience would have preferred to learn why,rather than how, massed start races are beingpromoted. He says that the importantquestions to be answered in this connectionare : (t) Do we want massed start racing atall, and, if so, why ? (2) Is it practicable toestablish such a system of road sport as apermanent feature of our national life as inFrance and other continental countries ?

Now G. H. S. does not like massed startracing. He has said so many times, and it istherefore not surprising to learn that " theanswer in each case must be in the negative."G. H. S. is, of course, entitled to his views,but it must not be presumed that those arethe views of the majority of cyclists. I amin favour of massed start racing, and althoughthat happens to be my perSonal preference,to my certain knowledge it is also the opinionof many tens of thousands of other cyclists.

It is true that I have had a few lettersopposing massed start, but those few representsomething less than 1 per cent. of those Ihave received in favour. Mr. Kain rightlyinsisted that his club was not a breakawayfrom the National Cyclists' Union. Of coursenot. I have already pointed out to those whowanted to " heal the breach " that therewasn't a breach, and if there were it shouldbe hailed, not healed.

G. H. S. is right when he says thatB.L.R.C. methods differ from the old styleof massed racing in England and from themodern methods adopted on the continent.They differ, however, only in detail, andthe difference is insufficient to provide adistinction. He says that in the past centurythe only massed start events were a fewscratch races such as the North Road " 24,"and the Bath Road " too " (the originalBath Road " too " Cup is in my possession.I am the only one to possess a Bath Road" too" Cup without having ridden a hundredmiles for it l), and club contests were con-fined to handicaps. Pacing was, of course,employed in the scratch events. The fieldssoon dispersed and the massed formation wasonly " temporary."

Such events were before my time, but Ihave debated the matter with some of theveterans who tell me that the massedformation was anything but temporary ;that in some of the events there weremassed finishes as well as massed starts,as G. H. S. admits took place in the handicapstowards the finish. Under the modernmethods the mass, he says, tends to remainunbroken all the time.

Unlike the continental counterpart, wherethere is some high speed racing in the townsand villages, B.L.R.C. events are neutralisedin the interests of public safety, and he thinksthat this renders B.L.R.C. events " a faintshadow of the continental prototype." Onthis score he thinks that no one can saythat this is a finer type of sport than the

By ICARUS

unpaced races that we have developed underour system of time trials.

With something approaching a sneer or atinge of acerbity he asks : " For what reasonare massed start races being promoted ?The argument that this hybrid type ofcompetition in which the riders lay off atintervals to parade through a town, to delivera message to a Mayor, or to receive a kissfrom a film star, will eventually give usinternational supremacy is not to be takenseriously." Unfortunately for these viewsit is taken seriously, in spite of the oppositionof those who would like the sport to remainon the hole and corner system, with itsaspenlike fear of intervention by the police,introduced when many of the critics wereyouths in the 'eighties and 'nineties.

He asks whether there is any possibilitythat the higher authorities will agree to it,notwithstanding the support of police officersand civic dignitaries. He rightly says thathighly -placed members of the Governmenthave condemned this form of road sport,but omits to say that it was an inspiredcondemnation, the inspiration coming fromthe National Cyclists' Union and the R.T.T.C.with supporting remarks in the Press, fromG. H. S. and others who, because they donot like massed start racing, think that youshould not like it also. The few inspiredpolice cases which have been brought againstmassed start riders (here again I think thepolice were " making a case " as a result ofinspiration !) have ended ignominiously forthe police and for massed start opponents.

" Is It Worth \While ?"

WITH a concern for the continuation oftime trials, a concern which I have at

heart, too, he asks : " Is it worth while torisk so much for so little? " My answer tothat is that no one in authority would havetaken the slightest notice of massed startracing, if attention had not been drawn to it bythose who vigOrously opposed it, not sincerelyon the grounds that it was dangerous, butbecause they felt that it would replace thosebranches of cycle sport in. which they wereinterested, either as officials or as com-petitors.

When the opposition started and thebogy of danger to the public was raised, Ipointed out how weak their case would be if asa result of experience of massed start they wereproved wrong. It was said that the absence- oftraffic on the roads when massed start wasintroduced during the war would give a falseimpression of its safety. Well, many eventshave been run since the war, when traffichas been well-nigh back to pre-war standards,without accident and without incident. Thefew " test " cases which have been broughthave been lost, and all of the evidence showsthat under the rules it is perfectly safe. Thecritics have been more than proved' wrong.

The point made by critic G. H. S. that, in itspresent watered-down form as compared withthe continental methods, it is not really massedstart racing, goes. No one pretends that itis. The fact is that it is a new form of massedstart, that it is wanted, and enjoyed by severalthousand riders and spectators, and that itsadherents are increasing.

The B.L.R.C. are in the strong position ofbeing able to fortify their arguments and toconfound the critics by the direct evidence ofthe police. There seems no end to whichthe opponents of massed start racing will notgo in order to get it suppressed. Many yearsago they proclaimed that such a form of racingwas illegal. It was left to me to investigatethe legal position, and to proclaim massed

start racing quite legal. A great deal of theopposition is, as I have said before, notpromoted by sincere concern for the safetyof the public, otherwise the practical demon-strations they have had of its safety and of thecare taken in running these races would cause.them to admit that they had made a mistake.Their real concern is that, having aroused theinterest of the authorities in it, the wholesphere of road sport has been brought into thelimelight. If one goes it is extremely likelythat the other will, too.

Does G. H. S. suggest that road recordsshould be abolished because there have beenaccidents ? Does he suggest that becauseDonovan was killed (to cite only one example)time trials should be abolished ?

The matter is to be further debated at -alater meeting, and I shall refer again to thematter` next month.

Perhaps the recent attempt by the N.C.U.to regain control of all forms of cycle sporthas something to do with the opposition.For I shall not tire of pointing out that theN.C.U., which professes such an interest incycle sport, 5o years ago abandoned all formsof it except racing on closed circuits. It nowwishes to control time trials again. In theunhappy event of that being brought about,we hope that the N.C.U. is entirely re-organised and that some fresh and youthfulblood is made to pulse through the arteriesof this old body which is suffering from atrophyand thrombosis.

It has not exhibited any great ability in itsrunning of track events since the war, and inmy view is a quite inefficient organisation andunrepresentative of the cycling movement itprofesses to dominate.

New Light Alloy RimQ MALL supplies for original equipment0 will soon be available of a new lightalloy rim specially designed by Dunlop fortubular sprint tyres. Its sizes are 26in.(weight III ozs.) and 27in. (x21 ozs.). Therim has flat side walls suitable for caliperbrakes, a reinforced base for strength andspoke tensioning, and a rigid bayonet typepegged joint. It is depressed and pierced fortrue tangential spoking and is suitable for alltypes of hub, with a highly polished metalfinish. The retail price is 78s: a pair.

Rhos -on -Sea Cycling Club (Affiliated to

the W.R.R.A.)AM informed that the N. Wales R.C.(B.L.R.C.) and the above club have

amalgamated and will continue as the Rhos -on -Sea C.C. affiliated to the B.L.R.C. Hon.sec. is J. P. Thomas, 15, Tan -Lan Road,Old Colwyn, N. Wales.

Road Accidents-November, 1947FATAL accidents on the roads of Great

Britain during November were thelowest recorded for any corresponding monthsince 1931. The total of 476 killed is 55fewer than in November, 1946, and 23 fewerthan in October last year. Non -fatal accidentstotalled 14,152, compared with 14,496 in thecorresponding month of 1946.

Adult deaths were highest among pedestriansand pedal cyclists, being 194 and 73 respec-tively. In the case of pedal cyclists there wasan increase of 14 compared with November,1946,

Child deaths included 74 pedestrians and8 cyclists, compared with 63 and 7,respectively, in the corresponding month of1946. It is disquieting that more than halfof the children killed were under seven years.


Wayside ThoughtsBy f. J. URRY

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,0121-3.ft,DAN-, r

One Good TurnTHE days of mellow fruitfulness have gone, but the

mists persist on occasion, and they are a bleakand oblique nuisance. To be sure we are better off onbicycles than in motor -cars when the grey ghosts ofcloud cling to the earth and the familiar places becomea phantasy merged in dirty cotton wool that clingsclammily and spottics your person and apparel with asample of the industrial haze. Usually I can find myway home without trouble and manage to dodge themaelstrom of blaring cars that congregate at crossroads ; and with a certain subdued sense of importancefrequently pilot a string of smoking vehicles as faf asI go along the road. It is quite a pleasant sensation toundertake a job of this sort, because it provides proofof the wonderful mobility of the bicycle when conditionsare difficult, and you undertake the small aid withoutany personal inconvenience, always provided thefellow on your tail light can stop, as quickly as you.And it provides a nice lesson in patience for the folkwho are not usually renowned for that virtue. Generally,the fellows who follow me home are pleasantly thankfulfor the slight assistance, and when in the mornings theelements have recovered from their bout of nuisancethe numbers of greeting horn -pips as overnight friendspass me on the way to work considerably increases. Iwish all road users were more partial to the improvedtempers displayed' when foggy conditions reduce alltraffic to a crawl for that would help enormously in thesolving of our road problem. I do not desire to reducetraffic to a crawl, when conditions are normal, but Iwould like to see a happier exchange of commoncourtesy between all road users, and a far greater careexercised when the ways are slippery with mud, wetleaves or silvery frost.

Autumn GloryUP to the middle of November my mackintoshes had

enjoyed the longest rest from their protectiveduties I ever remember ; or perhaps I had enjoyed itand my macks had lain dormant in the bag. Twice, Ithink, since mid -June I had slipped the cape on to resista passing shower, and its only other service was as asitting -mat for a wayside lunch interval when the dewhad not quite departed. It was indeed a wonderfultime for the outdoor folk, and I should think therenever was a finer cycling time than the late spring,summer and autumn. I had used up all my holidaytime before November, but during that month enjoyedone glorious week -end when the sun shone most of theday on woodlands rioting in colour as rich and warmingas in any late autumn I remember. With so dry gseason one would have thought autumn and its pageantof glory would be short, yet it was the longest period ofgold and russet beauty I remember. Its glory cameright up to the edges of the towns, and in some placesinvaded them, and I thought on my journeying howlucky we cyclists were to roam at a speed that alwayskept the pictures positive rather than a blur of visioninduced by speed. In the middle of, the supposedlydoleful month -you know, " No sun, no moon, no

. light, no noon-November ! "-I was out amid ourWarwick woods on a Sunday morning and they werethe richest thing I have seen on the eleventh month ofthe year. What a gift the possession of a bicycle is andthe ability to ride it comfortably ; yet how few folkrealise what they are missing. If they were shown thepageant of this autumn in Technicolor on the films,

go'4.311

C haleIsle of Wig 1-4

The weatherbeat et% oldchurch. overlookinq Chap13.19

many of them would enthuse about the vision ; yet itis, or was, down the mad for the youngest and the oldestto revel in from the saddle of a bicycle, and nothingto pay.

Still ShortWHILE the cycle trade is to be congratulated on its

. achievements in the export field, I'm afraid thatfact does not help greatly in supplying native riderswith the first-class ,goods they have been awaiting theopportunity t6 buy for so long. Ask any dealer and youwill find he cannot keep a stock_of good bicycles oraccessories. 'they are snapped up the moment theyarrive, and the high prices seemingly make no difference.Personally I find it most difficult to use myself to thenew sense of values : which I suppose is not surprising.for I was buying bicycles in the Victorian age, andbecame far more used to looking for reductions thananticipating rises. The fact is that the number ofhigh-class machines and their proper equipment willbe meagre compared with demand, and the luckyones among us who have decent mounts will be wise tocare for them more closely than ever. Thank goodnesswe can buy light tyres now, for the Sprite is back on themarket at, to me, an astonishingly cheap price, 8s. gd. percover, considering that the pre-war figure was 75. 6d.That fact will make a lot of difference,' it will enliventhe old machine no end, taking away that feeling ofdrag the wartime tyre induced, which was sufficiently.positive to penetrate consciousness. And I understanda new line in Sprites will soon be available, to be knownas the Tourist Sprite. This cover is a little sturdierthan the open -sided type, for its walls are protectedwith thin white rubber, and the tread is of a vigorous,non-skid pattern ; a good, sound light tyre for winteruse, or for the rough rider who likes to negotiate theremoter tracks. Yes, we shall have to wait yet awhilebefore we can make the ideal choice in bicycles orequipment, but the fact that first-class tyres are nowavailable is a lively step forward in the comfort ofcycling.

They Are GoodT KNOW quite a lot of people think I exaggerate1 the cycling value of light and lively tyres, and somehave told me they would prefer an added handicapin running quality for the sake of obtaining greatersecurity from punctures. Now, I've little recent experi-ence of the resistance of what are known as full roadstercovers, but I can tell you that my average of puncturesriding on the open -sided Sprites are three a year, onemore than was the case well pre-war, because of theincrease of the broken glass menace. Three thousandof my annual 8,000 miles are over city andsuburban roads, and half that town mileage is overgranite setts. I keep my tyres fully inflated andnormally do not wear them to the last bit of rubber,yet even so I get an average of 7,000 miles a coverprovided I escape the disaster of a broken bottlesegment when riding in the dark. That fate woulddeal just as severely with a roadster tyre. In return Iget a lively bicycle, and the comforting consciousness thatI am making the best use of my automatically decliningpowers. Personally I think the added tyre cost per annunibetween the light cover and the heavy one is no morethan ten shillings at the most, and what value for thelittle extra outlay At speed-which I, do not now

practise, because it makes me blow-I consider thedifference between the light and heavy tyre at least twoMiles an hour, and if you transfer that speed increaseto ease increase, it makes a very great difference to happ'cycling, and happy cycling is the fact I want to impresson all people, young and elderly, or in-betweens, whitlove the country, the ever-changing panorama of theroad and value the health of outdoor living.

The DifferenceIJRING the Christmas holidays I saw a lot of rayD . young ftiends off to the hills and the sea, gay,

little parties who made the four days' break a joyousjourney amid delectable places; to be candid I enviedthem such freedom, wishing them the luck to make themost of 'it while such conditions lasted. It remindedme of my young adventures half a century ago whenfew cars prowled along the roads and every inn had awelcome for the wanderer, while to review the foodwe ate would be unkind to -day and perhaps unwise.Once, when in North Wales, Boxing Day came in withstorms of sleet and rain, and Barmouth Bridge quiveredunder the impact of the wind. Nothing daunted, welads struggled along the coast road to Towyn, found awarm room and the considerable remains of a Christmasdinner to console us, so it was late in the afternoonbefore we reached Tal-y-Llyn, but the gale helped usto be in time for tea. Being fairly dry by then I wantedto stay the night, but the Sancho Panza of the pattywould insist we push on in order to shorten the home-ward journey for the morrow. So out we went, thefour of us, into the bleary night with the hail moreprominent in the descending moisture, and muchtrouble with oil lamps which "doused their 'glims "when a more fierce gust than usual came screamingthrough some crevice in the rocky passage. A brightthought struck our leader ; we would climb the hill toCorns and seek shelter there ; it was only four milesfrom where we struggled with the lamps. We did,and got a soaking from the knees downward for thepain of crossing the divide. And, believe it or not,Corris was locked up for the night at 8.3o, and wasapparently sound asleep. We awakened the custodianat the hotel on the right as you start to fall down thelong street, and he did his stuff nobly, building up a.huge fire from the smoulder. reaching down the hamand cutting thick slices half way round that great legof pig, and soon the eggs were added and the scentof it dismissed all thoughts of the howling storm." A nasty night it is whatever, not fit- for man or beast,"and We agreed. " But this will do you good indeed,"and it did. And my recollections of -the bill, with abreakfast repetition of the supper; was five bob. Yes,I've seen some changes ; no wonder I find it difficultto match to -day with yesterday, especially in the matterof prices.

Making GoodMANY years ago I knew intimately a youth whose

keenness for speed cycling was extravagant.Work and racing was his motto, and though his trainingfor " the littleness of life "-earning a living-washard, it did not appear to sap his wheeling energy, forhis greatest delight was to knock a few seconds orminutes off the last occasion on which he rode themeasured course. I expected him to mellow in duecourse, to see and love something of the beauty hepassed by -so swiftly. Then the accident happened.Early one morning on his way to work a car crashed into.him, and a third of the bones of his body were shattered.He was a long time recovering, pertly due to depression.His early industrial training was wasted, his wreckedbody could not do the job, nor would he ever moveswiftly again by his own effort. Life looked bleakindeed, despite a fair sum of money paid over as com-pensation. One day he came to see me with an adver-tisement offering a country inn. It would take all hiscapital and more. Could he make good ? And Ithought he could with the aid of the girl whom heforthwith married " for better or worse." It was abrave thing to do, the marriage and the purchase, theall or nothing. A year later the couple were learningby trial and error the duties and also the delights anddisappointments of host and hostess ; and they learnedslowly and completely. In his spare time the boy'searly training resulted in building a model of thecharming village in which he lived, a whole miniaturevillage in a garden, with its river, its church and itsinn. It was an attraction, a tiny loveliness in the greatglory of a lovely countryside ; and the couple pros-pered, learned their business thoroughly, added thelaughter of children to their fortune, and alwaysremembered they were once cyclists. There is a great-`welcome at this inn for the comfortable rider, and a1:happy recollection of those faraway days when some,roadside was busy in the pearly dawns, and numbers ofus-now growing old-were busily despatching th -

fleet -limbed youngsters of yesteryear. That is one othe memories worth committing to print, the happoutcome of a great disappointment. Of such stuare men and women made who ride bicycle; and fortifthemselves against " the slings and arrows of outrageoufortune."

4 GEARS AND GEAR CUTTINGEdited by F. J. Camm.

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CYCLORAMA"5,:,

'2.9

Among the Southgate BoysIKNEW that I should enjoy myself with

the members of the Southgate CyclingClub, when I attended their annual dinnerat the end of November. It was a most happygathering, presided over with dignity andcharm by the year's president-my old friendBallantyne. And what an enthusiastic lot ofcyclists gathered round the festive board.Good speeches (I except my own), goodfare, considering these austerity times, andthat sense of comradeship which I everassociate with cycling men : there is nodoubt about it-this game of cycling doespromote harmony and good fellowship to aremarkable degree. *Good luck to this oldclub-founded originally in the year 1882.

Curious Place-namesTHE Dunlop Company, I think, hit upon

a happy idea when they introducedthat current series of cycle tyre advertisements,featuring curious place names . . . those oddnames which many English villages bear, andwhich never fail to intrigue me. "Barton -in -the -Beans " is one in the series, and " Box'sShop " is another. One may meet withcurious names like this in many parts ofEngland, and I know of one keen rider witha love for the curious and out -of -the -ordinary,who has made quite a collection of them.But personally, I like best the " lovable "names, of sweet cadence, which one maycome across particularly in Cornwall. . .

" St. Just -in -Roseland " is one I recall, andI cannot think of a more beautiful name for avillage. To get back to this Dunlop advertise-ment series, I feel that it is always good toadvertise cycling, and not merely the bicycle.It is what a bike can give us, in the way ofhappiness, scenic beauty, and good health,which really counts.

-The Raleigh Industries Fair

THIS event, which attracted so muchfavourable attention, owed much to the

organising ability, and strenuous work, ofmy old friend Fred Keller, the advertisingmanager of the Raleigh Group. I met him atthis unique show, and congratulated him onthe excellence of the arrangements . . . theshow was marked by that good hospitalitywhich one ever associates with the Raleighname. Touring the show, and looking at

7.;' '''' '

111.e lands .Lncl,Cornwall

The 6rnouS Westernmost"Point of E.rtqland ,

Los ships Lighthouse.

that intriguing display of cycling clothing,presented in conjunction with the WoolSecretariat, I met several old Nottinghamfriends, and-as a loyal Midlander-felt thatI was back on my native heath for a fewhours.

The Good North RoadRECENTLY, and private en-

gagements have necessitated sometravel along the Great North Road, and inrenewing cycling acquaintance with this mostfamous of highways, I have recapturedsomething of its charm. Barnet, despite allthe modernisation which has taken place inthe recent years, is full of charm, and some ofthe "old bits" areuniquely historic. Anddown Galley Lane thereis an old and picturesquefarm where my small sonhas his pony . . . and it isgood for me to ride out tothis farm and watch theyoungsters putting goodcobs over jumps, and in-specting the sleek cattle inthe modern cowsheds,and imbibing, with a nos-talgic love, all the sightsand sounds of farmland,stable, and byre-whichwere my delights in child-hood days in the long ago.And the Great NorthRoad is one of those gctodhighways which retainssome historic and comfort-able inns. Not all havebeen spoiled by somemisguided brewer with apassion for chromium -plated fittings, and a finedisregard for the treasuresand traditions of the past.The low-ceilinged tap-room, the cosy bar, theblackened rafters . . . theseare the things I love in aninn.

"February Filldyke"

NOTalways do the

ditches run with rainin this the shortest month

sesp,"5.:.

iii

By

H. W. ELEY

of .the year. But February rain is good andbeneficial, and I always like to associate themonth with showers which kiss the cheekswhilst one is a -wheel, and my good farmerfriends smile when they see the rain -soakedfields, and hear the gurgle of the water in theditch. And, February brings us St. Valentine'sDay . . . when, in my far-off youth, sweet-hearts exchanged gay, colourful cards,pledging perpetual love. And even in thisunromantic age I see that modernised editionsof these amorous greeting cards are available. . . and St. Valentine is not forgotten.

And . . . Spring is On the Way!THE cold rain may beat on our faces

as we ride down the lane, and the treesmay still be bare . . . but it is quite possiblethat there are snowdrops abloom in the dellby Sweet Briar Farm. Shy, virginal blooms

. . . which have to be looked for carefully . . .

but what more lovely harbinger of spring ?

Plea for ComfortQUITE recently I was chatting with a

young cyclist in an inn. It was inhomely Hertfordshire, and I took a goodlook at his bike . . . and it all ended in mygiving him a lecture on the virtues of comfortin riding. Because that boy's bike neededa bit of attention ! The saddle springs hadgone . . . and how he managed to ride any.distance in any degree of comfort, I do notknow. And his tyres : sadly under -inflated !And brakes . . . a menace ! Such simplethings to put right . . . but then this was onlyone case of neglect I have met with recently.It really is surprising how many cyclists lettheir machines get into bad condition andsuffer therefrom. Now is the time, beforethe spring touring season is with us, to givethe mount a thorough overhaul, and remedyany defects. A comfy saddle, properly -inflated tyres, and sound brakes make such adifference !

p/7 -

;AO',"

-.17-7".1_.e',7: ;11

/I

In the louely vale ofei /CA't E. HA M.

Ike litHe curreti villagelying snugly beneath..Box Hill


My Point of ViewBy WAYFARER

"s411., ttr, 49)s) 1.

Parrot SayingTT is to be expected that we shall hear, ad-1. nauseam, statements to the effect that " thebicycle is coming into its own again," thanksto the abolition of the basic petrol ration. Ifthis means that many People who are unableto use their motor -cars and want a quickform of transport (preferably in fine weather !),will turn-probably in desperation-to thebicycle, then undoubtedly the statement is true. Inpoint Of fact, however, the bicycle " came into its own "very many years ago, and has always maintained thatposition, which is unaffected by the folks who drift awayand worship " other gods." The popularity of the bicycle-of cycling-endures. It endures through sheermerit-even when those who view- the magical two -wheeler only from the utilitarian standpoint cease toemploy it, thus casting aside the tremendous potenti-alities of the pastime. The cycling vogue is not madeof those whb are here today and gone tomorrow.

Open-air MerchantsIALWAYS feel slightly curious about the attitude of

mind of cyclists-fresh-air fiends, if ever ' suchexisted-who, on occasion, shut themselves up in ill- ventilated places. On a recent Sunday I entered thecottage where I usually obtain tea and found no fewerthan i8 fellow -cyclists ensconced. Many of them weresmoking (cigarettes and pipes) and the door and windowswere closed. I, who had just ridden 5 miles to reachthis rendezvous, did not fancy the atmosphere and openedthe door wide-and blocked it open. Nobody was anythe worse ! I recall that, when I lived in Birkenheadand crossed the River Mersey every day, a small groupof my brother-Anfielders were usually on the same ferry-boat. Like myself, they were keen on fresh air, andyet they made a point of gathering on the lower- deckin close proximity to the engine -house, where they couldobtain liberal draughts of warm oil! For my part, Ialways patronised the upper deck of the boat, wherethere were tons of fresh air.

Lonely Furrow'nY chance, on a recent Saturday, I had tea with aL.' collection of Midland cyclists, members of one ofthe oldest of our clubs, sharing, with them the almostinvariable torrent of badinage and leg -pulling whichenlivens such occasions. When the time came for meto start for home, I mentioned my proposed route andasked if anybody were bound that way. " You're toofast for us! " was the surprising reply, and, as theyrefused to put this valuable statement into writing, sothat I could use it as a testimonial, I was driven to theconclusion that the remark was merely a spill -over fromthe tea -table flippancies.

So, lighting my lamps, I set forth to plough my lonelyfurrow. - I had the vaguest ideas as to the distancelying before me. In any case, that point wasunimportant, and irrelevant-especially as I keptadding bits to my itinerary-and, three hours later, onreaching horne, I found 31 miles on the tally. Howpleasant it was, that serene travel in the dark, alongalmost deserted roads: turning here to the right, andswinging there to the left : intent only. on filling in thetime and having a quiet and happy evening. I happenedto be using a network of roads and lanes which cir-

summer by the Mole.

Looking across the riuer tothe little church of STOKE.DAtsE.R.N ON A fretisurechest -of monuments e brasses.including the brass of the fiat'Sir John D'Abernorl -the oldesttithe country dated 277.

cumstances have causedme to neglect for a fewyears; but I had nodifficulty, in the blacknessof the night, in finding myway, and in recallingwhere this switch or thatwould land me whentempted to leave my mainroute. I found, as I alwaysfind on the arrival ofautumn, all the old joysof night cycling, evenwhen the furrow is alonely one.

Active Participation-MY eye was attracted

by the followingparagraph in an articleabout mountaineeringprinted in one of thedaily newspapers a fewdays ago : " I climbbecause, in common withevery man-and manywomen-I need a re-creative spbrt i because,in common with a largeminority, I prefer to takepart in sport myself ratherthan pay someone else totake hazards while I lookon ; because, of all sports,mountaineering, to mymind, is the finest. I getnothing out of it excepthealth, strength, adven-ture, comradeship,

freedom, and a deeper sense of the endless magnificenceof our earth." What conviction that statement carries,and how admirably it is expressed ! Moreover, with thealteration of but one word (" cycling " substituted for" mountaineering "), how well it fits our great game.Yes, we who are enthusiasts for cycling propel thebicycle because we feel the ,need for recreatibn. Weview cycling as the best -ever pastime, and we extractfrom our chosen game just what our mountaineeringfriend obtains from his-health, strength, adventure,comradeship, freedom and education. The bicycleopens the door to all these tremendous gifts. Alas,that so many people pass by without realising theinfinite possibilities lying in wait for them ... at so littlecost. Other people, slightly (and only slightly) wiser,go through the open door and, lacking -enterprise, failto take their toll of the manifold delights and advan-tages which the' bicycle will provide. The pity of it !

Undesirable SystemAN ex -Serviceman, with whom. I ride pretty regularly,

tells me that when he was learning to drive amotor -car, which was part of the R.A.F. curriculum,he was reproved by the sergeant -instructor for leavingtoo much space for a cyclist who was being overtaken.My friend, as a cyclist of many years' experience,treated the wheelman as he himself likes to be treated-and thereby put himself in the wrong ! The statementcan be relied upon, and it appears to me that thereinmay lie the secret of some of the bad driving on thepart of Servicemen, which provoked so much criticismand condemnation during the war period. To reprovea driver for allowing a cyclist too much room seems tome to be part of a very undesirable system.

" Some" TyreTUSW before setting forth for a brief holiday a fewJ weeks ago I was fortunate enough to acquire apair of Dunlop " Sprite " tyres, and you may be surethat these added very considerably to the enjoyment ofthe tour in which I indulged. The mental effect ofriding " Sprites " was most marked, and I am certainthat there was a physical counterpart. Having reachedan age when any little bits of help which the bicycleas a whole can give me are most acceptable, I welcomedthose light tyres with both hands. The recent warstruck cyclists a savage blow when it put the manufactureof " Sprites " on the top shelf, out of the way.Personally, I did not do so badly, thanks to a spot offoresight and perhaps a bigger spot of luck, but mystock of " Sprites " ran out a few months ago, andI then had to take to fully-rubbered tyres. Howevergood these are, they do not possess the lightness and" life " of open -sided tyres, and I was accordinglymore than glad to get back to wheels shod in mypre-war fashion.

Immunity BadgeITmust be admitted that the immunity badge of which

I would now speak is not a badge at all, nor doesit ensure zoo per cent, immunity. Nevertheless, itbears some relation to that badge which is sold tomembers of the public, Who are then saved from beingpestered by sellers of flags and things in favour of somecharitable object.

This paragraph is the result of a conversation 'witha young friend who, when she lived within convenientreach of her office, was able to cycle to and fro, andshe claims to have thus enjoyed an almost completeimmunity from colds. Now, in changed circumstances,it is neither convenient nor easy for her to continuethe cycling act, and she has to rely on public tritiaport,with the result that, as she puts it, she is " getting coldafter cold." Further; a relative of mine is putting herhusband on an expensive cold -avoiding course ofmedicine, " as he has to travel so much on buses."For my part, I cannot help feeling that a better cure-or preventive-would he indulgence in cycling. Abicycle is available for his use, and while it is at timesadmittedly disagreeable to ride through unpleasantweather, it seems to me to be at least as disagreeable --at least, I say-to walk to" the bus, wait in a queue,and then to be crowded into a small space with a lotof other people, with the prospect of another wet walkat the business end of the journey, the whole procedurebeing repeated, in the reverse, at the end of the day'swork. Whatever else may besaid in favour of cyclingto and fro, the bicycle does take one from doorto door. There is no waiting : there is no jostling :there are no steamed windows, speaking of air whichhas been breathed again and again.

Alive and Kicking.THE recent delivery, in little over half a week, of

three cycling lectures at widely spaced townsgave me a like number of opportunities of linking upwith people who, because of my long -sustained workfor cyclists, are good enough to write me as an oldfriend. It was very pleasant to meet these people,some of them for the first time in the flesh, their previouscontact with me having been by correspondence, andthey mere able, uncannily enough, to quote bits ofadvice I gave them long years ago, and to repeatpassages from articles I had written, while some ofthem were good enough to thank me for forgottenservices I am supposed to have rendered. Here andthere one came across a feeling of surprise that, I wasstill ".alive and kicking," and still " getting 'em round,"those who have drifted away from the pastime beingprone; at times, to believe that I had done likewise.On this point I can only repeat what I said to thesefriends, namely, that when I find something betterthan cycling-and I've not found it yet !-I may bein danger of relinquishing the pedalling process. Ihave made a point of telling all these people that Iam still writing in this journal, and that The Cyclist.

. though merged for the time being with PRACTICALMECHANICS, will one of these days resume weeklypublication with a bang, and we shall then see whatwe shall see !

Day of DaysON the penultimate Sunday of November I set

forth for my usual 70 -mile_ ride without a pullover,and with a thin pair of gloves packed away in the bag.It was a grand morning, with, plenty of wind (whichcaused me to " step on it " at times) and a joyousmeasure of visibility and sunshine. A change came overthe scene as three of us dealt faithfully with a knife -and -fork (not to mention spoon!) lunch, and it was actuallyraining when our journey was resumed. At least, thatwas our impression. We were in no doubt half anhour later, when the rain came down in torrents-coldtorrents-and the wind increased in fury, There was

- a feeling amongst us that this form of madness wouldnot endure for long, and the impression was well based,but we hod no conception of the beauty which was tofollow. The rain stopped, and the sun returned toduty. An extraordinary translucent light was overeverything, and up above, where blue sky was notshowing, there were stupendous cloud effects, with arange of colouring which one seldom sees. The massivearchitecture of the heavens was indeed a joy to behold.The colour scheme gradually faded, and as daylightgave place to darkness we had a final glimpse of thedistant hills, seen at an earlier stage of our journey.

Tea at a small country cottage formed a mightypleasant interlude. There was a glowing wood fire,and the mom was pleasantly warm. The welcome wasjust as warm. The food was plentiful and good, andour table was lighted-if " lighted " is the word to use-by a small oil lamp. Then oueinto the night again,to find a nearly -full moon on duty ; to find, also, a muchreduced temperature, making the wearing pf glovesdesirable. Thus the Three Musketeers went their way,weaving in and out of deserted lanes, now riding insilence, now talking of old times, and all the whileenjoying to the full this day of days-which they feltit to be. A day to remember-a day to look back uponwith pleasure, if only because of the magnificence ofthe aspect when the afternoon's fury had died away.So another joyous Sunday passed into history, withanother 7o miles of pleasure to be recorded.

"Practical Mechanics" Advice Bureau. COUPONTills coupon is available until February 28th,1948, and must be attached to all letters contain-ing queries, together with 3 penny stamps. Astamped, addressed envelope must also be enclosed.

Practical Mechanics February, 1948

Published about the 30th of each month by GEORGE NEWNES, LIMITED, Tower House. Southampton Street. Strand, London,W.C.2, and Printed in England by W. Speaight & Sons, Ltd., Exmoor Street, London. W.10. Sole Agents for Australia andNew Zealand-Gordon & Gotch (A/sia), Ltd. Sole Agents for South Africa-Central News Agenoy, Ltd. Subscription Rates(including postage) : Inland, 10s. 6d. per annum,. Abroad, 105. per annum. Canada, 105. per annum. Registered at the G.P.O.

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" PIGMY" ELECTRIC MOTORSLow voltage, reversing for models. Usethe famous "PIGMY" motor for your Boats.Cars, etc., the most powerful motor obtain-able. Weight 9) ozs., 2iln. x 2lin, x2 to 24 volts. Price 25:-. Send 2(d.for leaflet.Ex -Gov. Motors, 24/50v. A.C.D.C., 3lin. x21tin. Ball Bearings, 25:'-. 12;24v. D.C. BallBearings, 2iin. x Din. x 12/8. With10/1 worm gear, 18/8. Worm gears, 10/1 :vase. lin. x llin. x stn.. EP-. Satisfactionguara.nteed.-E. M. Co., 120, TorringtonAvenue. Coventry.

RATCHET & REVOLUTIONCOUNTERS

k for 42 111Leaflet No 8/Speed up to V6,000 r.p.m.

B. & F. CARTER&Co. Ltd., Bolton 5

Sets of ('LEA It DIAL RA MS andINSTRUCTIONS for making EASILYWORKSHOP BENCH, SAW BENCH,LADDERS, STEPS, LATHE STANDS.WIND CHARGER MASTS from"L"section METAL (obtainable at ZeroCost). Price 4,6. Posted promptly.As advertised.-P. Robert. Les Buttes,

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ADANA PRINTING MACHINESPrint in the odd hours with anAdana-still the most absorbing

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SAILOR SAM'S SECRETHow to make

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84 - or

NO MAN CAN KNOW TOOMUCH OF HIS PRODUCT

78'

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BRITISH ;NIA DE

The Ultra Lens is a revealing eye of sixactual diametrical -36 area magni-fications, which brings out points ofstrength or weakness. Whether you

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The Ultra Lens Company,75, Finsbury Court, Finsbury Pavement,

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The WINCHGeared hand wheel, with positive drive to /in.Flexible Steel Cable. Suitable for adapting to :

Wire Strainers, Light Winches, Clothes LineStrainers, Street Lamp Winches, Children's CarSteering Wheels, Boat Steering Wheels, CentreBoard Winches, Sail Winches, and many otheruses.Inquiries welcomed from Manufacturers andWholesalers interested in large quantities.Send 71- p.o. for sample, with wire.

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WOKS :L.N.E.R. or G.W.R. Nameplates (each) 2i-L.N.E.R. Locos (2nd edition) ... 243" Planning and Layout " 3i-

' " Two Rail Electrification " 3/6Fowler & Starner Locos. ... 6/6" British Loco. Types " 8 r-

LINESIDE BUILDLNG KITS :00 0FootbridgePost

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TYLDESLEY & FIOLBROOK (M.E.T.A.)109, DEANSGATE, MANCHESTER, 3.

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NICKEL PLATINGComplete Equipment, including NickelAnode, Plating Salt, etc. Full instruc-tions for Plating Ornaments, CarFittings, and all Metal Parts. Flash -

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DILDALUIHNAND ALI:MINDED SHEETSDuralumin 36 in. x 24in.. 2/-21 S.W.G. 481n. x 36in., 121-

x 36in., 1St-.Aluminium. In sheets up to 6ft. a 3ft.20 S.W.G. 1/10d. per sq. ft.On all above, add 2d. per sq. ft. carriage.Inquiries invited for various sections.COMPETITION CARS, LTD., TheOld Maltings, Nayland. Nr. Colches-ter, Essex. Tel.: Nayland 334.

The Institute of Practical RadioEngineers have available Homo StudyCourses covering elementary.theoretical, mathematical, practicaland laboratory tuition in radio andtelevision engineering ; the text issuitable coaching matter for I.P.R.E.Service entry and progressive exams. ;

tuitionary fees at pre-war rates-aremoderate. The Syllabus of Instruc-tional Text may be obtained, postfree, from the Secretary, 20, FairfieldRoad, Crouch End, N.8.

BRIGHT ALUMINIUM SHEETS.llin. x 12in. x 7in. x 1/16in. full, Is. 3d.each, or 12/6 doz., including postage.Reduction on large quantities.-Apple-yards, 72, Infirmary Road, Sheffield, 6.

NEW Machinery.-Electric Motors,Band Saws, Drilting Machine, Pumps,Grinders, Welders, etc.-John P. Steel,Bingley.

PRACTICAL MECHANICS ".-October 1933, June 1944. 127 copies,good condition.-Dromgoole, 167, TurneyRoad. S.E.2I.

SPARKS' DATA SHEETSProvide detailed descriptive matterand Full-size Constructional Print ofDesigns Tested and Guaranteed by

L. ORMOND SPARKS.MY LATEST DESIGN :TILT "CHALLENGER" PORTABLE.An Outstanding A.C./D.C. Portablehaving an Exceptional performance onMedium and Long waves. The circuitis a TRF. 3 -Valve Plus Rectifier, giving31 watts on the ' locals.' Good range,and quality. No complicated adlust-ments. Station -named slow-motionDial.. gin, StentOrian Speaker. TheIdeal Set for the home. Radio in anyroom. No Aerial or Earth required. 2/9

THE PORTABLE POUR. A T.R.F.All -Dry Portable. Medium waves ... 2.6ALL -DRY 3 -VALVE PORTABLE.MIL Waves. A Noted Set ... 2/6TINY TWO PORTABLE. Mediumwaves. 21in. Speaker 2/6ONE -VALVE PORTABLE. MLwaves. All -dry. 'Phone Sias. .. 26THE EMPIRE TWO. An All -waveAll -dry 2-Valver, Very popular .. 2/6COMPACT TWO. Medium and 'Longwaves. (Batt.). Speaker results ... 26T.R.F. 3-VALVER (Batt.). Mediumand Long waves. Fine results ... 2/6FOUR -VALVE T.R.F. SET (Batt.).As above with P.P. Output ... , 2/6S.W. SUPER TWO. (Batt.). *A fineDX receiver, widely used ... 2,6MAINS SETS A.C. .TWO-VALVER (Plus Rest.).M/L waves. 30 watts Output ... 2/6A.C. THREE-VALVER (Plus Rect.).T.R.F. Circuit. M/I, waves .. 2/6A.C. SUPERHET. 3 Valves, Plus Rect.,All -wave. 4 watts output - 2/6TILE UNIVERSAL FOUR. A 3 -Valve,Plus Rect. A.C./D.C. T.R.F. Set.MIL Waves. Amazing Power ... 2168 WATT QUALITY RADIOGRAM.A.C. Medium waves. Quality ratherthan range. P.P. Neg. F./B. ... 3/6AMPLIFIERSTWO -VALVE (Batt.) 2/6THREE -VALVE Ditto. P.P. ... 2/6A.C. 30 WAIT. Fine Power ... 2/68 WATT. A.C. P.P. Neg. F.B. 2/68 WATT Ditto, A.C./D.C.... ... 3/6

Many other Tested Designs in Sleek.Stamp for Full List and with Order.

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L. ORMOND SPARKS (31),9, Phoebeth Road, Brockley, S.E.4

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CAN YOU PLAY THE PIANOIf you are a nuisie lover, whyhave you not arqUired thisenjo pubis accomplishment andgreat social asset) Doubtlessbecause the prospe$t of prac-tice I practice I pfactice ! hasdismayed and discouragedyou. * elms is seldom less

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A Really Universal Motor" A.C.- D.C." Car. Paid

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1 pint Spray Guns ... £3 10 01 pint Spray Guns ... £2 0 03 C.F. Compressors ... £9 10 06 C.F. Twin Compressors ... £22 10 0Air Chambers with Gauges £3 10 06in. Saw Benches ... £10 0 0Heavy Duty Jig Saws ... £20 0 0Air Hose, V. Belts, Pulleys, Gauges,

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Documents

NOTES ON OPTICAL CALCULATIONS NEWNES · International Electronics, 7 -valve, 3 wave-band, covering 16-400 metres. Latest Brimar single -ended valves, variable BFO, Stand-by switch,