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ARTILLERY lVL\.P I~E.ADING AND ELE~lENT.AltY GUNNEItY }\[j\.DE EA.SY.

Artillery Map Reading and Elementary Gunnery

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    ARTILLERY lVL\.P I~E.ADINGAND

    ELE~lENT.AltY GUNNEItY}\[j\.DE EA.SY.

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    AR"rII~LERYMAP RE.f~DINGAND

    ~I~l~Ml~N'l'A]{Y GUNNEI~Ynl.f~DJ~ EASY

    BY

    4' GUNL.AYEI~" AND "CONTOUI~"

    FULLY ILLUSTRATED

    LONDON: GALE & POLDEN, LTD.2, AMEN CORNER .. PATERNOSTER ROW" E.C.

    WELLINGTON WORKS .. ALDERSHOTAND

    NELSON HOUSE .. PORTSMOUTHOBTAINABLE Ot' ALL BOOKSELLERS.

    THREE-AND-SIX (Net)

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    P.3.374.

    ALDERSIIOT:PRINTED BY GALE & POLDEN. LTD'

    WELLINGTON WORKS.1916.

    (Copyright under th6 Act 0/ 19 J 1)-

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    PHEFACE

    This book has been written with a VIew to providingin a, handy form knowledge of artillery map reading andgunnery sufficient. to furnish an adequate working b~sisfor both officers and non-commissioned officers. \Vhileembracing principles that have always formed a recog.nised part of artillery work, it is directed pre-eminentlyfor pre&ent-d~y purposes, and is largely based on facts.arising out of the present. war.JrU(j,

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    CONTENTSPAGB'

    CHAP'fER I.-LOCATION OF POSITIONS ON SQUARED l\!ApE..Division of Maps into Squares-Location of PointR-To obtainApproximate Rang-es-Protractor for Locating PositionR ...

    CHAPTR:H H.-TRUE AND MAGNETIC SORTH.Mag-netic Variation-Bearing's 4

    CHAPTER III.--8UEEl' LINE EUROB.True MeridlanR-To Find Sheet Line Error 6.

    CHAPTER IV.-SCALES.Representative Fraction-Statement in Words-Scale Line-VOtnparative Scales ... ... ... ... .. ... .. 8.

    CHAPTER V.-IIn.L FEATURES.Contours-Verticlli Interval-Horizontal Equivalent-Con-cave and Convex Slopes-Spurs and Re.Kntrant~ ... ... It

    CIIAPTEH VI.-l\IUTUAL VISIBILITY.To Draw a S.ection-Proportional Rise or Fall of E)'e.Line-. Skeleton Section-Comparison of E)'e-Line and Ground-Ang-le of Sight Method ... ... ... ... ... ... 19'

    CHAPTKU VrI.-BASIS 0[

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    -viii. COI\TENTSPAGECHAPTER XII.-DllUWTOR8 AND LINKS 01.

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    -K

    . ..,_---,,6-- ..,I

    1'0 filet "tUJI! 1.

    --..--.......---

    Fig. 1.

    -- -I

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    B

    ARTILLERY MAP READINGAND

    ELEMENTARY GUNNERY---"" ....,.-..---CHAPTER I.

    LOCATION OF POSITIONS ON SQUAREDMAPS.

    1. DIVISION OF :MAPS INTO SQUARES.}. Maps are first divided into large square.s by means oflleavy red lines caned "sheet lines." These squares arede:tt.ered with block letters A, TI, C, etc. They areblVlded by thinner sheet lines into smaller squares num-d?f?

    2. LOCATION OF POINTS.l~o~ition of x is centre of square D. 7.d. \Vheu'POSItIons-are to be located other than in the centre ofthese small let,tered squares, e.g., y, one must considero~h line of the square to be divided into 10 pa,rts, assown fOf D.6.a,., that is, the square is divided into 10C

    Smaller ones.RULE.-Start from the lcft'-hand bottom corner of thes~uare and estimate the number of tenths along the sheethne until bene,ath the position, then estimate the numberof t~nths up the square. Thus P is a point at the inter-s~chon of the 9th line along the square and the 7t~1~ne up, and its position is D. 6. a. 9. 7. Similarly Y IS.7.c.2.2.The following positions should be car{>fully noted:-

    1\1= D.5.d.0.5.N = D.8.a.5.0.A.M.R.

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    2

    D~1I~~~~l~:%r'or simply D.2.'V=D.6.d.5.5., or simply D.6.d.Great a.ccuracy cannot be obtained in loca,ting K bythis way t .sin.

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    4

    CHAPTER II.TRUE AND MACNETIC NORTH.

    The earth may be considered asa great magnet. Ithas its magnetic poles, which are near the poles of rota-tion. The north magnetic pole lies about L.at. 700 N.and Long. 960 'V. (roughly, north of Hudson nay).This attracts the delicate needle of the compas1s, andthus compass readings are also called magnetic readings.

    1. ~IAGNETIC VARIATION.The angle between the diredion of a magnetic needle

    and the direction of the north pole (i.e., true north) iscalled tho variation of the compass.This variation is not, co.nstmlt. It ha,s a slight annualchange, and also differs according to one's position-Greenwich, 150 21' 'V.; Ypres, 130 45' "V.; Maubeuge,130 10' 'V. This variation is shown on military ma,ps by

    a conventional sign. (See map.)2. nEARINGS.

    The compass is marked up to 3600 in a clockwisedirection, and a.t first it is advisable to read all ooaringsfrom the map in a clockwise direction. The Service Pro-tractor is graduated from 10 to 1800, a,nd from 1800 to3600, the latter numbers being used when the ohject orta,rget is left of true north.A magnetic bearing is greater than a true bearingwhen taken in a clockwise direction.VARIATION 'VEST.The magnetic north lies west of true north.Thus, given variation 150 west, a bearing 70 rightof true north is the same as a bearing of 850 right ofmagnetic north sinee the variation is added, beoause agreater angle must be formed with the magnetic line,

    which is 15 'V. of true north.0

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    5~gain a bea,ring from the map is read 3550, which is

    e-qulVa,lentto a magnetic bearing of 3700 or 100VARIATION E,AST.b M~gnetic north lies east of true north. A magneticlearlll~ is less than a true bearing when taken in aOCkwlse direction. Given variation 100 east, then10 right of t,rue north is the same as 600 right ofragnetic nort~. Aga}n,?o right of tr~e north is 50eft of ma,gnet'lc, or 3,500 nght of magnehc north .. To take a bearing from the map, place the J.>ro-tractor so that the centre x, Fig. 2, is on your positIOn,r.nd the edge of the protractor parallel to a vertical sheet1ne. Alwayg read from the 00 at the north. Th.ea.ngle required will be where the line joining your POSI-bon and, say, the target, cuts the edge of the protrado1r.EXAMPLE I.-See map.You are standing at N.E. corner of Ba,rwell Farm~.1~.C.2.9~, and by means of the protractor take theea,nng to right-hand corner of Jail Farm B.9.c.6.0.. T;ue bea,ring is 670, and therefore the magnetic bear-

    Ing 18 82.EXAMPLE 2.From A.16.c.0.8. you take the bearing to St. John's8hu:cl~E.3.,a.5.2. Since this is left of true north read

    ]8 lllslde numbers on the protractor.. True bearing is 225; that is, the magnetic bearingIS 2400h T~u~ up to this point all bearings have been rightbe.ar~ngs, a,nd the variation has been added to a trued'~anng to. co]]v~,rt i~ into a magnetic bearing. But thelre~to~s and dIal slghts are marked to 1800 left and:80 flght. Thus bea,rings over 1800 must be sub--racted from 3600 and ordered left.3 For e.xample, a bca,ring of 2350 magnetic is the same asGO 2350 1250 ldt of magnetic north.Again, 1850 right= 1750 left of magnetic north.J In !~xample 2 above, the magnetic bearing is 2400tlns had to be ordered for a line of fire for theflreetor it would have to be given as 3600 2400 = 1200eft.

    ~

    - =~

    -

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    6

    CHAPTER III.SHEET LINE ERROR.1. TRUE MERIDIANS.

    True meridians are marked on the top and bottommargins of the map, and in some caoos the correspondingmarks are joined by a faint black line. (Belgium'u~uu maps).

    If the sheet lines a,nd these meridians were pa,ranel, aline drawn making an angle equal to the magneticvariation left or right of a vertical sheet line 'would bean accurate magnetic meridian. When the slH)et linesand the true meridia,ns a,re not pa,ra.llel the discrepancymust be ascertained and allowance a.lwa,ys made.

    2. TO FIND SHEET LINE ERROR.(Boo map.)

    Measure the distance in yards from sheet, line AB tothe meridian at the top of the map, and again a,t thebottom. The difference between these dist.a,nces, 100yds. 40 yds. = 60 yds., gives the distance the sheet linehas fallen away from the true meridian (in this CUiSe leftof the meridian).To change this error into minutes mUltiply the 60

    yds. by 3438 and divide by the range across the mapfrom top to bottom. (See p. 27.)

    r ., 60 x 3438 3H'

    -

    ==== ~

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    7Since the shee1t line has fallen to the left of the true

    lneridia,n the error is "left." To draw a magneticm ']"e~l( lall from one of the sheet lines la.v (Iff an all~le e,f5 21' (t'he variation) less 34!' 14 46!' left.Similarly if the error ha,d be,en, say, 39' right, to get

    a.1~a.gne,tic melridian from a shoot line layoff an angle of5 21'+39'= 16 left. :.:;j(JL' b .)rf)'~ /~d.H the true meridian cuts a ver4ic,!1,she'e~!,line.\.tbet l&tance.from the vertica,l line a,t the ~9P must be. added;~:o~.istance at the bottom to obtain .~J~?~o~a,~jstances Th~ rough rules given on pp. 30Iana /69 will giveUffiClenily accurate results. IJ. j: ',.". ( ; [ I,1Tl1e top and bottom margins of SOIDo- ,foreign ImapsSlOW the meridians marked in two form~.)~ rtr:'l?-r;q',

    I, Se 'I 't VIl'it :i.1I .-.il:I xagC&lma, unl s. "1)'(,' "'f" ""1'1160 seconds (60") 1 minu'te,.J- r., . ".('Jli;ll

    60 minutes (60') = 1 d:gree;,,,. 'I' n J~90 degrees (90) = 1 rIght ~?!!le, ...:. ry,.It' lInk_Il.,] I.2. Centesimal units. '~n;n 'Jd b[lHI'lI

    100 minutes (l00") = 1 grade: J:'j''',', ,:f2 C"i'i100 seconds (l00') 1 minute.lle ,'Ji.,.lW': d100 grades (100 II) = 1 right 'anglt' ,rh ;ll (, 'lo ; Jj~!nnl~

    l~flJJ,n 1n ,'"

    ",;!';d J,,: t .' I;'::

    -"

    =

    __

    ~~

    j

    =~

    =

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    8

    CHAPTER IV.SCALES.

    A scale denot.es the proportion which a dist,a,nce be-tween any two points on a map bea,rs to the horizont.aldistance between the same two po,ints on the ground.Scales are shown in throe ways:-

    1. A REPRESENTAT'IVE FRACTION.A Representative Fraction (R.F.). Thus ~n-!TIlfor 1 :!O.OOO mealJS 1 unit of length on the maprepresents 20,000 similar unit,s on the ground.This unit may be an inch. Then 1 inch on the maprepresents 20,000 inches on the ground (roughly ! of amile). .A R.F. enables one to construct a scale for any ma,p.A Russian map with a scale reading versts and sagcneswquld be rarely intelligible to English troops, but if italso showed a R.F., say, 4n-&n-n-. a,n E,nglish scaJe maybe made, since any English unit may be' assumed. Thus1 inch on the map may represent 40,000 inches on theground; or 1 foot on the map may represent 40,000feet of country.

    2. A STATEMENT IN 'VORDS.A statement in words, as 3 inches to a mile,2 miles to an inch, etc. A R.I". may be quickly con-verted into a statement of inches to a mile by dividingits denominator into 63,360 (inche,g in one mile). Thus

    "fO~(f(f 20000 63360'2-=-- 0'3:160=

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    9d' ~r.a R.F. may be converted into miles to an inch by1V1dmg the denominator by 63,360. T'husTn-!rrn- 63360)40000'00('63 miles to an inch.

    38016 1984 00.~ 190080The .fonowing R.F.'s and their corresponding stare-

    lllent.s III words should be readily recognised :-In-!n-n-= 3'16 inches to a mile, or '3 miles to an inch.Tl}!on- = 1'58 inches to a mile, or '6 miles to an inchlrn-~n-n- '79 inches to a mile, or 1'2 miles to an inch.

    Trru1rron-= '63 inches to a mile, or 1'58 miles to an inch.3. BY A GRADUATED SCALE LINE.

    f By a Gradua,t,ed Scale Line.-See scale line at the foot0, map.To CONSTRUCT A SCALE.

    If Given R.F . Tll-&mr construct a scale to read 5,000lllet.res." (1 met.re= 40 inches approx.)Note what the scale is to read. In this case metres.One inch on t.he map represents 40,000 inches on theground, orOne inch on the map represents 1,000 metres on thegrolllnd.now many inches will be requhed to represent 5,000~()ILres As ma,ny inches will be required as the num-

    '('i1' of times 5,000 contains 1,000.Thus a 5-inch line represents 5,000 metres,

    =

    =

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    c:)C)Q C)c:)"'"

    () ......() u.:10\)0....

    , .

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    11th This line, if divided into five equal parts, will read10o~sands of metres. Sub--divide the first division intoequal parts, each of which will represent 100 metres.th The greatest care must be taken in the selection of()l 11 b7'7 um ers represented by tho parts of a scale line.di"~ 8crt!e must be a handy one; that is, one from whichti~ances may be read very easily and without calcula-})i 11:. Such numbers as 275, 125, etc., must 00 avoided.of ~lSlO?S should show 1,000, 500, 100, 50, 10. Sketches10 ort.Ifications should be provided with scales to rrod'1 I yards" while an art,illery sca.!e line should showdi~~~drods," and if po~sjble fifties," in the first largoIglon of tho line.su[~~ ~eale line shown in Fig. 3 may be divided andtCl1UlvIded with an ordinary ruler showing inches anddCl . IS of an inch, but occasions arise frequently that.11a.nd a more difficult operation."C'yard;:;,t'll It (j'. T"{)~"{)"{) construct n. scale to read ;',000Pro hIna m t e R.F. one ma,y state that 1 yard on thes~trepresents 40,000 ya,rds on the ground. Con-tha~e~ntly 5,000 will be represented by k of a yard;, IS, 4'5 inches.

    th~~ra,w. a ~ine 4.5 inches in length and bear in mindYO~ }tIllS lme (~ever mind its length, 4'5 inches, oncedivisi1ave drawn it) represents 5,000 yards, and suitableaolld tns must be made. Let the line read thousandslundreds of yards.'1'}1i ]"". .}II\l'1I11 (1\'181011 may be performed in the .usnal, way wIth011' drillers. If the protractor alone IS available, setlill/ll IIllgle (Of abollt 20 degrees) from both ends of the

    Cn '(p~f theRe /lng-Ies arc made exactly the E'ame AB andII', jIg. 4) will be parallel. Along these lines, startinglel~/}~ tl/(~ (,17d.~ of tlie s('ale line, mark off five equallatg )hs (preferably inches since tenths will be requiredl'hcr , alia then connect them as shown in Fig. 4.pa:t:~ connecting lines cut the scale line into five equal

    "

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    13Of?~obtain the sub-division for hundreds of yards, marktion,el~ths of an inch (or 10 equal paris) on the construc-8truct~nels .(note very carefully which parts of the con-" T~on hnes a,re selected), and proceed as before. .the V,Ot houses are 3 inches apart on a map. By ~acmgIt l!~ Me found to be 2,400 pa,ces apart. \Vhat IS theI)a' . of the map Construct a scale to read 5,000,C

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    14

    CHAPTER V.HILL FEATURES.1. CONTOURS.

    On milita.ry ma.ps hill features a.re most commonlyrepresented by contours. A contour is an imagina.ry line of level dra,wn throughpoints that are the same vertical height ahove sea IEWelor other convenient level. A contour thus forms theirregular boundary of a horizontal pla,ne a.t a fixed height "above datum level.

    In Fig. 5, A and B are the same vedical height (10metres) above datum level, a,nd consequently stand onthe same contour. Again, since the figure shows twodetached hills, C is the same height als H, and standson a contour, also numbeved 10. From the sectionshown in Fig. 5 it is se,en tha.t nand C are points oneither side o,fa saddle or col.2. VERTICAL INTERVAL (V.I.) OR CONTOURINTERVAL.V.l. is the vertica1 dista,nce between one contourlevel and the next. It may be given in fc'et, metres,etc. On the maps at present in use the vertical intervalis given in metres, either 1 mehe or 5 me,ke's. In J!"ig.5 it is 5 metres.

    3. HORIZONTAL EQUIVALENT (ILE.).ILE. is the distance in pla,n between two points.In Fig. 6, An represents a sloping road from A to n,and ne (equal to four times the V.I.) shows t.he differ-ence in level between A and B. An is the dista,nce onowould have to walk along the road to get from A levelto n level. AC is the distance as it would appea.I' onthe map; that is, the horizonta1 equivalent for the road

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    15.

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    16

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    17I[~,f C?urse, it will a,t once be noticed that AC, the..... , IS not exadly equal to AD, the actual distance~n ~he ground, but the difference is so slight that it may'0 Ignored in slopes up to about 15.By' d . .F' a companson of the contours an section IIIa1g: 5, it, will be seen that the closer the contoursUppe,a,r au tlhe map the steeper must be the slo~ef ley represent. In FiO'. 5 the distance from D to E ISiar lle.ss t?an t,hat fromb G to II, and yet the differences~, c,vel IS 5 metre,s in each case. Consequently t,heope from D to E is steepe'r than that from II to G.

    4. CONCAVE AND CONVEX SLOPES.G ~n Fig. 5 the slope A to K is COllC(we; that from Z tols C01/vr,:c.

    I It is~,f the, greate,st, importance th~t these slopes should~olre'adIly recogniscd on a, contoured map. It would Leee at first, to adheore closely to the following rule.toOrnrnence at the bottom of the slope and travel to the''P. Then:a,n~' If the slope is first gentle (contours well apart),(c then a.s the top is reached the slope becomes steeperontour I t I .c oser oget leI') the slope IS concave.tl 2. If. the slope is steep first and then more gentle as

    l(l top IS rea,ohed it is convex.gXAM I'LE I.-See map.Fro St['11 meyne House A.3.a. to Cross Roads on Steyno1 A.4.d. is a concave slope.p",XAMPLE 2.

    Slo~::le Road, from R4.d.2.2. to E.8.d.2.0. is a convex.1 From this it will he seen tha,t siQ11aIIinO'may be con-lluete 1 f b b-' ( rom the foot to the top of (l, concave slope.sl Again a, ba.tt,ery can be hidden from view by a convexwfNel, a.nd generally the lower part of a convex slope)e Included in the dead ground.

    A.M.n. C

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    185. SPURS AND RE-ENTRANT'S .

    .A t first difficulty is often experienced in distinguish-ing spurs and re--entrants as sh0'wn on a contoured map,and until one can reany imagine tha,t the oontours,me,rely require pulling up or out as a concertina, thefo~lowing might well be observed.(1) A Spur, Sanent, or Bluff.-Sta,nd oln the

    higher ground and look towa,rds the lower. If the con-t.ours go out from you the feature is a s.pur.rig. 7

    -50pos ition OJ]I/(r;f)er Ground

    (2) A Re-entrant or Valley.-Again stand all thehigher grOUnd.and look towa.rds the lower. II the cen-ltours come tOWQ1'ds you the feature is a re-ent'rant.

    Ftg 8. Poslhon on. Ilty/iC?P Ground_70~V,l. ~?"

    ______ 50For definitions for basin, base, brow, cresit, col, defile,

    .

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    19

    CHAPTER VI.MUTUAL VISIBILITY.

    , It is neicesisarytha,t o,ne should by an examination of,}, COI t "I' II"loured map be able to select smtab e sIgna. mgand ,b .' ..1'] C servatlOll stations and battery PO~HtlO11S.IOUO'] th\v'u b I In some cases obstacles not shown III e mapUI be found to obstruct the view, the correct part ofdIe. C()~llltirywill ha,ve been selected, and only a slighteVIaholl from the original point will be required.w,~enCirally, a spur, salient, or bluff, or a convex slopeq~' . obstruct a view, and with practice these can bein(~ck~yl'c'Cognised. On the other hand, genU} undula~-i b gl?'und often pres(mts difficulty. 'Vhen III doubt Itt~ advisahle' to dra,w a section of the ground lying be-.veell tIl t .. ., {)wo pomts III questIon.

    1. TO DRA \V A SECTION.1'a;4:Y a pi,ece of paper along the line, say, Observer toI'U' get: (If po'ssible use ruled paper, and. place tl~eov.Cd hnes pa,ra.]].elwith the line aT. Squared paper ISdrOll. more useful. This will obviate the necessity ofaWIng pa,rallellines.)(\a~ow travel along the line aT and mark and numbercontour cut by the ooge of the paper.re_N'ote carefully where the line aT crosses spurs andth entrants. Lot the horizontal parallel lines representVoe1:'cont:ours, and the spaces between the lines the5 ~lca.] Intervals .. Since the vertical interval is onlya'll .otres, which would be represented by about T~lr ofex Inch when the scale is 7J"l}~1fO' it is necessary tol'tggerate the V.I. to make the section practicable.li~~:xaggeration may be, say, 20: 1; but as a rule theshould be ahout t of a,n inch apart. (In anyonec 2

    ''

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    20section the lines must be e,ractly the sam,e distance apart.)Number these lines a,t either end, the numbers rangingfrom the lowest to the highest of the contours involved.Now drop perpendiculars from the marks o~ the edgeof the pape1r to their corresponding llO'rizolntaJ lines.The points at which these plfpel11dicubrs meet the hori~zontal lines give the position of the contours: on the sec~tion. Connect up these point,s, noting that hills ha,ve a-crest above the topmost contour shown, and re-entrantsare slightly deeper than the lowest contour.It will now be evident wheHler 0 and T a,ro visible ornot.EB represents the oog-e of the paper put against

    A.14.b.3.6 and Park Inn E.8.b.2.2. The po~nts a,twhich the contours cut the edge of the paper have heetnmarked, and spurs and va.lleys indicated by + and .Once the section is drawn, t.he following points ma,y

    be decided:-1. By wha,t verlica1 he,ight the ta,rget is visible or in~

    visible, and consequently height of object. which may beused as an observation station. Allowance should bemade for intervening buildings and trees.

    2. How far in line of sight one would ha,v' to walk toseo a dista,nt object.3. 'Vhat ground would be invisible to t,he enemy.4. General nature of the ground for an advance.Tho following methods may be uood, and with practice

    very accurate results may be obtained.2. PROPORTION AL RISE OR PALL OF EYELINE.Select a crest or rising ground beit,ween posit,ions of,

    say, Observer and Targett, such that, it will be visiblofrom 0, but may so raisel the eye line that it will passabove T. (The selection of this point at first pres,entssome difflculty, and consequently draws much from tho

    -

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    21

    '0.It)

    -~- ------- - _._- - _. -----

    .~. - - - - - - - -- - - - - -- ----~---- - -- - -- - - - - - - -_ ..

    .~--------------'------- -11:1 --10.g--------------------- -- -- --.:::}-------------------- -- -- ---S}----------------- ---- --

    .~-._._-----------------

    CD

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    o-It),,-~J~

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    22Having found the int.ervening point, measure the

    range to it from 0, and not.e the riso or fan in the levelof tho eye linel to this point.Now measure the tota.! dista,nce from 0 to T, a,nd find,

    by means of a proportion sum, what, the, eye line wouldrise or fall in this total distance.The fonowing examples taken from the, map show the

    working of this method.(1) Rise of Eye Line.Can an observer at E.2.b.5~.1. see Jail Farm

    B.9.c.5~.O ?Intervening cres.t~spur (55 ro.) at A.16.c.O.5.Height at O's posit.ion 40 m.Height of spur 55 m.Range between these two point,s = 1,400 yds.

    :.eye line rises 15 metres in 1,400 yds.'Vhat would it rise in total distance 2,900 yds. ?

    _ 15 x 2000 _ :~1 metre~.1400

    It rises 31 m. above O's position, i.e., 40 m. + 31 m.=71 m.

    Bllt the foot of Jail Farm iH abont 58 m. :. it is in-visible unless the farm is at least 13 m. high.(2) Fall of Eye Line.Can Cross Roads E.1.d.0.7 be seen from spurA.12.d.1.6 ?Intervening crest is knoll in A.15.c.Height of spur= 70 m.Height of crest = 55 m.Distance=1,700 yds.

    ==

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    245. ANGLE OF SIGHT METHOD.

    Calculat.e the angle of sight from A (say Observer) tothe intervening crest, and also from the crest to B (sayTarget). If the first angle is greater than the second inelevat.ion, then the line A-crest-B is convex, and con-wquently A and B are mutually invisiblo.In the case of depression it will be just the opposite..-ift1u first angle is smaller than the second, the two points

    will 00 mutually invisible.EXAMPLE.

    Can a man on the Road at R2.a,A.7, with glasse,s,see the top of Beacon Hill in B.7.c.2.2~Intervening crest is edge of knoll in A.15.c.Angle of sight from Cross Roa,ds to Crest = 60' E.Angle of sight from Crest to Beacon Hill (63 m.)=7' E.111ereforc the two points are mutually invisible.In thew examples particular care must be ttlken inselecting the crest that breaks the eye line botween thetwo points.

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    25

    CHAPTER VII.BASIS OF CUNNERY RULES.

    r' The majority of rough rules for artillery work are de-a1ved from the circle. At the centre of any circle theretoO 3600 subt,ended hy the circumference. The circum-ercnc'Oequals 11" times the diameter D.( 22)11" 3'1416 or 7" approx.

    c I'

    57-3

    D{ J!I~A

    Thus 7r n subtends 360.:. D subtends 360 360 1,260 114'5454.

    7r 2~ 117"

    =

    = = =

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    26But the diameter D twice the radius It.

    i,e.,D=2H.:. :l H 8ubtends 114'5454.i.e., R subtends 57'2727.

    Or 57'3".Draw a circle of any radius. Measure the radius round

    the circumference AB. The a,ngle BCA is caned aradian, An arc equal to the. radius subtends 57'3 "atthe centre. This is true for any circle.Imagine a circle of 57'3 yds. radius; then the arc AB

    would be 57'3 yds. and the angle subtended would be57'3. Thus every yard in the arc will subtend 10 atthe centre of the circle. Make AD equal 1 yd. JoinDC.

    1. TRIANGLE OP REFERENCE.The triangle CAD is called the C C T'ria,ngle ofReference. I,If the student constructs a triangle with II (i.e., DA)

    one inch, and AC 57'3 inches, he will see what a slope(CD) of 1 really is, To make the triangle practicable,the angle at C in Fig. 12 has be,en exaggerated.

    c57 .5 j/d s.

    LJ].IYdA"

    Now consider AD as a height II (ydB.), and CA as aT:1.11ge R.Thus H. for an angle of 10 and II of 1 yd. 57'3 ydB.

    10 ydB. 57'3 x 10100 ydB. 57'3 x 100

    2 100 yds. 57'3 x 100

    =

    =" =" =

    =

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    27Now 100 yards=H and 2=D degrees.

    17'3Thus R=HxDor D x It II x f>7'3 (60 used for rough rules).r H x 60 D x RfhenD=---and HH. 60

    If the angle is required in minutes.60 mins. 1 degree.:. M x R=II x 3438 (Le., 60 x 57'3, or 3600 approx.).This formula is uSd in ca1culatinO' sheet line error

    (Chap. III). 01 height is in feet--h. (ft.).

    h=31IThen D x H=h x H)'l( i.e., of 57'3. )

    Again, if minutes are required-M x R= h x 1146 (i.e., 60 x 19'1, or 1200 approx.).

    N .13.-1 0 is subtended by 1 yd. at distance of 57'3yds. (60), i.e., 1 min. is subtended by 1 yd. at rangeof 3600 (3438), or 1 min. is 8ubtended by 1 in. at rangeof 100 yds.This forms the basis of some of the rules used forestimating deflection.

    2. GRADIENT.From the triangle of reference it will be seen th~t fora slope o~ 10 there is a riso of 1 yd. in

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    28Now 1 yd. is the II or V.I. and 60 is the R or H.E.

    Th d. G V.I. Hus gra lCnt ILK or ]:N.B.-The numerator and denominator must be of thesame denOln1'nation and the numerator a.Iways 1.To Find a Cradient. Se-o Map.From Cross Roads EA.d.2.3 to E.8.b.2.4.Height of EA.d.2.3 = 52 metres.Height of E.8.b.2.4. 72 metres.

    :. the rise or height 20 met,res.

    -40 "302010

    A

    A

    III

    I10 :~j

    I,IIIIIIIII

    =

    ==

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    29

    ""

    ""

    The range between these places = 4'00 ~etres.20 1:.G= 400=20.

    \Vhen giving Ule< gradient of a road for military pur-pa,sies it is obvious that the gradient of the steepestpa,rt must be known., For example, supposing the road to ascend a concaveslopo as in Fig. 13.T1~en the gradient of the part CB is the gradientr~qulred, since en is the steepest part of AB (contours

    c oser together).J)(-!Jrees.-From the triangle of reference it will beSeen that to convert a slope in degrees into a, gradient

    Wo must multiply by l(J'10 slope correRponds to G of 60

    2 160 or 305 160 or 12.

    The range is shortened. by increase of slope.Again to convert a gradient into a slope in degrees wemust multiply by 60.

    G d. t f 1 60 (' d' f 1 6ra len 0 _=_=-,4 . .Jra lent 0 .15 15 10. Tn exam pIe Iibove grad ien twas -i(J' therefore the slope111 degrees would Le {-~ or 3.

    ~

    -=

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    30

    CHAPT'ER VIII.THE ANCLE OF SICHT.

    J. TO OBTAIN ANGLE OF SIGHT I"ROM MAP.(See definition, p. 91.)

    Consider Fig. 14 a,s a section of the ground frombattery to ta.rget.BT is the line of sight and TnX is the angle ofsight.

    K r .B ~(jO.YdS'

    40Yds ~OyYh.'];'19' j/l

    TX=the difference ill height of B a,nd T, which is60 40 yus. 20 yds.nT=Uange=4,OOO yds.From formula in Chap. VII-

    ~l x It II x :UWO .. ~[ H x _~,GOO.. It.. If' 1 20 x :U-;OoThus in above example the ang e lJ !)lg it -wo-U-'

    From this we see that the hundreds in t.he COlista,nt

    - =

    ==

    =

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    31t RULE.-Reduce difference in height of battery andarge1tto'inches a,nd divide by the hundreds of yards inra,nge Th" . I t' d .' IS gIves mmutes e eva Ion or epresslOnbove example 18' E. Consider 1 metre ~O ins.Example. Se,amap.Battery E.7.d.2.&. Target B.ll.d.O.O.Measure the range 4,800 yds.lIe1ight of battery 60 metres.Height of ta,rget= 39 metres.Difi'erence= 21 metres.

    7 5Angle of sio'Tht ~L>!' :10= 35 17 Js-' Depression..)!J2

    Order 15' D.N.H.-Always be ca.reful to state whether E or J)The a,ngle of sight is put on tho guns to 5 minutes.

    't SUpposing an angle of sight worked out to be 18' E,1 . would be o'rdered as 20' E' but if it were 18' D itWouldbo ordered 15' D. '1 It is generally advisable to over-estimate this angle forc eva,tion, and under-estimate for depression, in order tog'et high bursts, and to ensure tha,t the shots go wellover when firinO' aO'ainst trenches owing to tho oftenVe~ 0 0J nn,rrow spa,ce bet,ween our trenches- and those of theonemy.

    2. DIRECTORS.(a) Nos. 1 AND 4 DIRECTORS.

    a1 X no a2 X oT+or ---nr +or --nT+ el~vlltioll.

    depres~ioll.

    = =

    ==

    = =~~ ~

    _

    - -

    =- =

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    o

    32Observer can measure aB by sub~base, or r~nge find~er,or rough estimat.e by amount of telephone Wll'e, maklllgan allowance for obstacles.Range aT is found by range finder, and BT by meansof the plotter. .

    Fig.1S.

    Bal angle of sight from B to a.a2 angle of sight from a to T.The angle of sight is taken from 0 to B, a.ild thereforeits sign must 00 changed to obta.in angle from Il to 0,since angle of elevation is equal to angle of depression.Angle of sight from a to n=3 D.Angle of sight from to T= 1 30' D.Find angle of sight from n to T.Angle from a to B=3D, ... anglo from n to 0(Le. at) 3 E.It will be found simpler to work in minutes and keepthe sarno denominator for both fractions.From the formula we get:-

    :!O. + ( ....I~~ x 5~0) + ( ~0 x 345~ )f~;0~1 0~;00 I

    4 4100 345_ -245'_6P'D 10 ()+4 4 -4-- 4 , say .

    ==

    =

    -

    -- - -

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    T\VO SHORT METHODS.(i) Estimate what fraction no upon BT is-say

    500 13600 '7 approx.Take + of al } of 30=25'.Now OT . . II TI f I h 1iT IS practIca y 1. Iere ore eave t e aug e

    a2 alone. Now write these two as in formula.25' 10 30' _10 5', say 10 D.

    tl (ii) Find tlle apex angle at T and multiply it bytIle d~grees in the angle of sight from 0 to B. Changeate Lng? and call the product minutes, and add it,ge raIcally, to the angle of sight from 0 to T.Apex angle=8}o. (See page 69.)Angle of sight 0 to B 30 D.

    3 l( 8}= 25' E.25' E + ( 90') 65' D.tl NOTE.-This rule is used to calculate the difference inB~ angles of sight of flank guns of a battery on a slope.b . corresponds to the battery front, and slope ofattery is a 1

    (ll) No.3 DIRECTOR.To set up the Director.

    1. See that the deO'ree scale plate with its micro-meter I d d b d' h . . tlea , an the clinometer in ex WIt Its mlcrome erlead, are at zero. (The micrometer head reads minutes.)hI'2., Mak~ t~,e two pairs of arrows on ~he carrier andackets cOlllcIde by means of ~he levelhng screws.3. The bubbles on the degree scale plate must belllade cent,ral by adjusting the legs of the director.A.M.R. I>

    ==

    _ =

    =- =

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    34'1'0 J[t!asw'e the .A ngle of Sty/tt.

    1. Lay closely in the direction of T and clamp thecarrier, using the lower levelling screw for elevation andthe slow traversing sCtrew finally for line to get crosehair lines of the telescope on T. The plane of thedegree scale plate is now depressed or elevated for theline 0'1'.2. Measure tho horizonta,J angl'e TOll, laying onB for elevation with the upper levelling screw (do nottouch the lower) and for line with the micrometer headof the degree scale plate. The plane of the degree scaleplate is now depressed for tile Z,ine DB.3. Swing tho eye piece towards the battery past zeroto the extent of the a,pe,x angle BTO.NOTE.-Two lower screws for T, and two upper screwsfor B.4. Now level the bubble of the sight clinometer forthe angle of sight B to T.

    Reasons for the abo1'e procedure.a. \Vhen the telescope is swung from the line aTto the line on the difference in slope 01' and OB,

    that is, the slope from Target to Battery, is recorded.b. By swinging past zero to the extent of the ape~angle the telescope is placed in a line parallel with theline B to T and the clinometer C C holds," though notshown on the scale, the reading for the angle of sightT to B.c. By bringing the clinometer bubble back to its

    central position the telescope is brought from the line'1'13 into the horizontal plane.3. CLEARING CREST Ii'HOM MAP.

    EXAMPLE 1.Hattery A.1.a.8.4. Target n.15.c.5.5.

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    35On obtain this, the quadrant angle that would be puta. I 0 gun to hit T must be known, and also quadrantUng 0 to tho crest. The quadrant angle is composed of10 angle,s of sight and elevation.

    Angle of sight to '1 ' 40' D.Range 4,[lOO yds.or angle of clevation say 9 10':. quadrant angle t$0 30' E.Angle of sight to crest 50 E.Range 600 yds.or angle of elevation 45':. quadrant angle 5 45'

    . O'rThereforo, since the quadrant angle on the gun istl e~terthan that required to clear th'J crest, it followsla, the trajedory will clear this crest.p",XAMPLE 2.(IUfOil' 4 ange to a target 4000 yards. Angle of elevation800 000 :rds. is 8 10'. Angle of sight to target 2 30' D., batt.~ds. III front of battery is a crest 200 ~t. higher th~ntho /Y: Angle of elevation for 800 yds. IS 11'. 'VIII,ra'Jeetory clea,r the crest 7To clea,r crest:-

    Angle of sigbt = 5 E.Angle of elevation = 1 I'Quadrant anglo 6 l'Anglo on gun:-

    Angle of sight 2 30' D.Angle of elevation 8 10'Quadrant angle = 5 40'Therefore trajectory will not clear crest.

    1

    D 2

    ~~

    ==

    ==

    ==

    ===

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    36

    CHAPTER IX.THE PRISMATIC COMPASS.1. TO TAKE A DEARING.

    Hold the compass by means of the ring, let it resthorizontally on the backs of the fingers and bring theprism quite close to the eye. Looking through theprism, move until the hair line is on the object. Theprism may be moved up and down in its slot and thuSbe focussed. The numbers on the dial will be observedto be oscillating. If the dial plate is swinging toOfreely, check very gently by means of the check stop.'Vhen still, read the number indicated by a prolong~'tion of the hair line, e.g., 50. Then the object is saIdto have a oompass bearing of 50, that is, it is 50 rightof the magnetic north.'Vhen using a dry compass, difficulty will aJwaySbe experienced in getting the dial stationa,ry, andreally satisfactory results a.re obtained only whellthe compass is resting on, say, a plane table, a gate pos~'etc., provided no iron be nea,r. This disadvantage 1Sobviated by the liquid compass. Since the dial is set inoil there is little oscilla,tion, and conSquently greateraccuracy is obtained with little loss of time.

    2. INFLUENCE OF ME,TAL.Ca,re should be taken to soo that no iron or steel benear the compass when it is in use. Keys, pocket knives,etc., are sufficient to ca,use deflection. Keep at least

    10 yards from the guns. Do not st.and near railway,tramway, iron fencing, bridges, ete. Troops witJh sidearms will affect compass. for a considerable diM:.anC8.Do not take a bearing standing near anorther parBOIl

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    37.3. CARE OF COMPASS.

    ce~se the check stop very gently and wait until thedial rehof the oscillation is rea,ched. Always clamp thelifts 7 en .not in use, by means of the locking stop. Thisleath he dIal off the pivot. If the stud is in front of theVenter C~lse,place the glass window to the back to pre-Po,sslble breakincr of the glass when fastening stud.tn~;ob1d the glass be broken an emergency hair linehOle e o~tained by passing a horse hair through the

    S provIded in the lid of the compass.4. TO TEST A COMPASS.It .~hoUl~seJttremely important that the error of a compassaccu be known. Take a bea,ring off the map veryCon ratel>, to a weU defined object that can be recognised.erroVert It to a ma,gnetic bearing and allow for sheet linecomr. Then take the bearing with the compass and

    baa I?a,re. The difference will give the error. Three,fInO' t 1noted o~ a .ea,st should be taken an~ t~e mean errortin . A pleoe of paper gummed wlthm the rubberPla~ at the ba,ck of the compass would form a suitableon which to record the error.5. USES OF THE CaMP ASS.

    (1) To obtain direction of N. and S., etc.(2) To take a bearing to target, or aiming point, et.c.(3) To SAetor orient the map. (Soo Chap. X.).

    Xr(4) To find ~ne'8 position on the map. (See Chap ..).?n~~led:nserting places on the m.ap that are not alreadya. t;ake a compass bearing to the object and convert it totna,k~ereading. Place the protractor on your position,and ~g sure the edge of it is parallel to the sheet linesOn th~a,~ forward ray. The object must be somewherethis IS Ime. Now, from your position, mark off alongray the ra,nge to the dista.nt object.

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    38If the rango is not known, walk to another positionand again take the bearing of the distant obje'Ct. Set

    this ray off on the map, and whero the two rays interwctwill be the position. The value of a third line will be~een from Chap. XI.,\ .

    (6) To give a line of fire from magnetic north, usingthe compass in oonjunction with No. 1 Director. (SeeChap. XII.).(7) To give angle to a t~rget from an aiming point notmarked on the map.e.g. !fag. bearing of AP 1400 R.l\Iag. beaTing of T < ,900 R.

    Angle from Aiming Point to Targ,et = 500 L.(8) Day and nig7~t mrtrching.-Suppose a compass:bearing of 1200 is required. Release the milled edge and,turn it round until the metal indicator is opposite 12"that is 1200. Take care to notice that the index bar onthe glass coincides with the metal indicator, since the glass'of the compass sometimes becomes loose. Lay the corn~

    pass down and open lid out flat. Turn it round until theneedle is beneath the index bar. Then the line of ma,rehis shown by the hair line, or by the line from the centreof the dial a,nd over the two luminous patches in thecompass lid. In order to march in this line it will beadvisable to pick up some prominent star, if possible,about 200 to 300 a,bove eye level. Owing to the move-ment of the stars, the direction should be asce,rtainedevery 20 to 30 minutes and another star chosen on which.to march.(9) To find approximate rallge.-Ta,ke a compasSbearing or the object a.saCCttrately as possible. vYalk 100yards to . right or left and take a,nother bea,ring~Difference of bearings will give apex angle.

    e.g., 1st bearing 1120

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    39J1 x 60. 100 x 60Now R I.e., -_~~_-D :!A6,000 ~tholls:lnds.:!} 2~2~ thollsands.52,400 yds.

    a '1'11118 when the base i~ 100 yards the rule is-divide thepex angle into 6 and tho answer is ill thOllSJ.lld8 of yards.r .T~() g~ea.test care in reading to fradions of a degree iseqUlred to obtain anything approaching the true range.

    = ---

    = =

    ==

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    40

    CHAPTER X.SETTINC OR ORIENTINC A MAP.

    Setting or ori.enting a map means placing it in such aposition that it corresponds with the a.ctua.lground, Le.,the north lines on the map point to true north.

    It ena.bles one to identify objects, buildings, a.ndfeatures around, a.nd to locat-othem on the map withgreater easo and a.ccuracy.1. METHODS OF ORIENTING.

    (1) With Compass.a. Open tho compass out flat and place it on the con-ventional sign for true and magnetic north, so tha.t thehair line of the glass lid a,nd the notch on the ring a,redirectly over the magnetic line. Now turn the map round

    until the arrow and compass needle are pointing in thesame direction.b. A more accurate and convenient method is asfollows :-'Vith protractor, set off a ray from a vertica.!sheet line, making an angle equal to the va.riaHon, ha,ving

    a.lIowed for sheet line error This is Ule,n a ma,gneJticnorth line. Proceed as a.bove.c. 'Vhen a protractor is not available, and map isfolded in a case. Note the variation, Bay 130 W. Open

    the CQmpassout flat and place it on one of the verticalsheet lines (or, better still, on a meridian, then no sheetline error need be allowed for), so that the hair line andnotch on the ring are directly over it. Then turn mapuntil the needle is pointing 130 'V. of the sheet line.(2) Without Compass.

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    42Turn the figure XII to the sun, and hisect the angle

    made with the hour hand by the line from the centre tothe figure XII.N.D.-The minute hand is not required. Sun is sout,hin northern hemisphere, and north in southern hemi-sphere, from posit.iona outside the tropics.

    Difficulty may occur in pointing the hand exa.etly tothe sun. Hold a match upright, in the cenke of theglass. This will cast a shadow which should be a. pro-longation of the hour ha.nd.Fig. 17

    .J ' 8a, the hour hand; and c, the sh&dowof t,he ma,toh b,should form one straight line.

    (2) By Night.

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    43si.rnila,rla,titudes. Since an stars revolve round an in-~Isible point (~he Pole) it ~oll()w5that twice. in everyhours Polans must cometmto the same vertIcal planeWIth it.

    "*

    IIIII

    t1 .' ~f':-: ....... 1'of~1II~Jt

    . Fig. 18 shows the relative positions of the stars form-Ing tho Great Bea,r, or the Plough.\Vhen Zeta (second sta.r in tail) is vertically above orhe,low Polaris, then the Pole Star is true north. At

    other times Poh.ris is approximately true north, a.nd canho recognised by aid of the "pointers," as in diagram.In tho southern homispher') the constellation known

    as tho C C Southern Cross" must be recognised.

    ~

    ~

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    4tConsider it a.s a laJ"gekite. If the ma.j.ora.xis.Depr~duced 4~ times in the direction of the taIl, a pomt WIllbe reached almost over the south pole.

    Fig 19

    Or hold a piece of }J'

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    CHAPTER XI.TO FIND POSITION ON MAP.

    ~e!ore starting operations it is necessa.ry to fix one'spo~nbon on a map. This can very often he done roughlyby recognising the relative pOlSitionwith regard to sur-rounding count,ry as compared with the map; near crossroads, on a spur, to right of a wood, hut to left of aquarry, ete. For a,ccura.te work an accurate startingpoint is essential.

    1. BY A SINGLE BEARING.If the observer is near some hedge or road which hecan recognise, select an object, e.g., church, windmill,btc.,. which can also be recognised on map. Take theearmg with a Prismatic Compass, say 100. Since~N. 7.No.

    8S.

    Fig. 20.Ot; r"tion. 01'Observer.found ..

    *'. ,

    J80.rs.this bearing must be plotted on the map, subtract thevariation, say, 15. The true bearing is then 85.Place the knot of the protractor on the object, and maketl:e protr:actor run true north and south, that is parallelwIth the sheet lines. Mark the direction of 850 Join

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    46this point with the object (church o~ windmill) andcontinue the line back until it cuts the road. Wherethe ray cuts the road will be ithe position.N.D.-The error of the compass and the shoot lineerror should be allowed for.This may also 00 done by a single raJ if a range finderis present. :Mark off the range along the line from theobject, and this will give position.

    2. RESEC1.'I ON.If the observer is in very open country, e.g., marsh,heath, it will be seen from the previous method that oneray is insufficient. Two objects at least must he recog-nised and their bearings taken. Where the two baderays intersect will 00 the position. It is always advisa,bleto take three bearings where possible, the third ray drawnbeing a check on the accuracy of the work.Example:

    . ....}J. j'l9'A, TI, and C are three buildings recognised on the map,

    0:

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    :47B 220 ; c 780 The variation, say 15', is deducted. from -each leaving true bearinO's of 3000; 70; 63.Place. the 'protra.etor on A and 0m.ark the point 300.StartIng from this point, draw a hne back th.rough A.Proc~ed similarly for Band C. \Vhere the hnes meetat x IS the required position. It frequently ha,ppens thats~an triangle occurs, as in Fig. 21, known as thetrIangle of error."It may be due to inaccurate working, or to an error in

    the compass not a.Ilowed for.

    C.

    tl In Fig. 22, showing the error exaggerated, supposeIe error in the compass is right. Then the position, ~:nnot be on the right of the lines A, D, and C. Thus. Ck~lUot be in 2. or 4, looking towards A; or 3, 4, or 5,.~ lUg towa,rds n; or 4, or 6, looking towards C. Thus1 can only he in l.n ~i~ilarly, if the compass error is left, the pooition can-hr~"' .'0 on the left of the lines A, B, and C, a"ld thus itsl'VlOltIon can only be in 4.

    ~ =

    ~

    ~

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    48The correct position in 1 or 4 would be 3J position

    whose distance from the three rays is proportional to thelengths of the three rays.A simple rule, and fairly a,ccura.te, is as follows:-Ifthe triangle of error is large, work again; if small, takethe centre of it.The following example is worked on the map:-Compass bearings 0'-

    1. Reunion House, B. 6.c. = 3052. Chaw's Farm, B.6. b. = 3583. Destructor, B.8.a. 68 ! fPosition found is B.ll.a.5.9.

    3. RESECTION BY ALIGNMENT.Set the map as accurately as possible and identify onthe map two or three objects that can be seen in thedistance. Place a pin to mark one of these objects andanother in line with this pin and the object itself. With

    these two pins as guide a line drawn back from thedistant object will pass through your position on themap. The intersection of lines similarly drawn will givethe required position. (Always look past the lower partof the pins when placing them in line.)

    4. ADJUSTMENT.Three positions or objects must be recognised. Set upthe director at zero with the sight rule or telescope onthe first object, say A. Swing from A to TI, and read

    the angle recorded on the director-49 ; then swing toC and read the angle-125.Now take a piece of tracing paper a,nd rule any line

    =

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    49Ma.rk any point P in this line to represent your position,an ,se,toff from it the two angles as in Fig. 23.th Now a,?just this piece of tracing paper to t.he map soa.t the hnes A, B, a,nd C pass through the obJects A, B,

    F~.23

    ca,n~ on map. Then P, the point selected, wiIl be thePOsItIon on tho map. This method is very accurate, andCa,n bo very quickly performed.

    A M.H. E

    ~

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    50.

    CHAPTER XII.DIRECTORS AND LINES OF FIRE.

    Since the No. 1 Din~dor is gnera.ny ava,ilahle, andforms a good introduction to the use of others, it ma,ybeadvisa,ble to give a short description of this insrtrumentand its uses. Severa] old methods of obt.aining require,dangles are detailed below since the present war a,ffordssuch varying conditions of Artillery work that, both oldand new methods should be known.The No. 1 Director consists of a gradua,ted brassplate reading to 1800 right a,nd 1800 left. Above thisplate are two movable plates which can be clamped in.

    dependently by means of screws. The uppe,r of thesetwo plates supports a sight rule. An index a,rrow ismarkd on the lower plate.To Set Up the Director.-Spread out the legs of theDirector well to give the inst,rument good support, andseo that the graduated plate is horizonta.I. Pla,ee' 180.towards the target so tha,t, zero will t,hus be brought

    under the eye. The arrow should be clamped a,t ze~o,and the upper screw loosed.\Vith No. 1 Director the index arrow is movahle sothat right of zero is (l right" and left of zero is " left."\Vith No. 3 Director the short white index mark or

    (l reader" is stationary, while the gradua,ted plate its:eIfrevolves, making readings right of zero (l left.," a,ndreadings left of zero " right." \Vhen using this inst,ru.ment remember " white is right" j that is, white leUe,rson black enamel.\Vith No. 4 Director the degrees are marked left orright, e.g. 40 L.

    USES.1. To Measure an Angle between two Distant

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    51(a) \Vith No.1 Director.

    h~Vith a,ITOWclamped at zero lay on one of t.he distanto ~oct~ and then clamp this line by means of the upper:crew. Loosen the lower screw, and swing on to thet~cond objed. The reading shown on the plate will give'le angle beltween the two points.

    (b) 'Vith No.4 Director.Cd~Vith the arrow clamped at zero.by means. of the milledtlbe SCl'eIWla.y on one of the dIstant obJocts through'Ie telescope,. Clamp the thumb-screw and lay onse:ond object by loosening the milled edge screw. TheR1row th . . l' t.__: ..en m~lca,tes the angle bet,\\"een t 1e t.wo pom s.

    2.. To Obtain Approximate Range.1'lTwo men 0 and B axe a measured distance apart.othey lay on the taxget at zero, and then lay on each'cr. Th.e ancrles TOB" and" TBO" are thus 1'a-~~~ded. 'The a~gle at T, the apex angle, will then be'rh .0, lesiS the sum of the angles" TOB and" TBO."

    e approxima.te ra,nge may now be found by means of

    the formula D (See Chapter VII.). It.3. To Cive the Battery Angle from a DistantObserving Station when 0 (Observation Officer)

    can see B (Battery).

    E 2

    ""

    = ~

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    52

    B---x

    The angle required IS Target~Da.ttery-Observer, theangle TBO. ,(a) Measure the exterior angle TOX. \Vith No. 1Director lay first on T, and then clamp the line aT.Loosen the lower plate and lay on D with the sight rulethe reverse way; that is, foresight next the eye. The

    foresight in this operation passes from T to X, thusrecording the angle TOX.Now, since the exterior a,ngle T'OX is equal to thesum of the interior angles at T MId D, the lla,ttery Angleis equal to the angle TOX less t.he apex angle. (SleChap. XIII.)(b) The Battery Angle may bo obtained withoutlaying on D foresight next the eye-an inconvenient

    operation with No.3 Director. Measure tho a,ngle TOB.Since the three angles of a triangle together equa.11800, the Battery Angle will be equal to 1800 l

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    54

    T

    B

    Fr.!!. 25

    A

    may now prooeed as in 5 a,hove, since t,he a,ngle ABTcan be taken from the map with an ordina.ry protractor.(b) The following method obviates the neoossity foractually drawing the ray from 13 towards A. Tako theTrue bearing of the line 13T from the map and convertit into a, l\Iagnetic bearing. The diff-eronce between thel\Iagnetic bearing of A and that of T will be the a,ngle

    from aiming point to targt.The following examples show varying positions of Aand T. Variation is ta,ken as 15 \V. :_(1) True bearing of T 163, and compass hearing ofA 80 right.

    Magnetic bearing of T 163 + 15 1780.j:?>

    = ==

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    55(2) True hearing of T is 127u, and compass hearing

    of A is 239.Magnetic bearing of T will be 127

    0 + 15 142.Angle from A to T is 239 _142 = 97 left.(3) T is 40 left of true North, and compass bearingof A is 50 (right, or clockwise, since takenwith a compass). T is 40_15=25 left of

    magnetic North.Angle from A to T is 250 +50 75 left.

    7. To Obtain Line of Fire when given the MagneticBearing of T .

    (i) a. With Prismatic Compass and No.1 Director.-Place 180 towards the Target to avoid unnecessarylllovement of the sight rule, clamp the lower plate at zeroand loooen the upper screw. Place the compass at theend of the sight rule with the ring over the backsight,~o th:at by looking through the prism, the hair line onhe lId of the compass and the sight vane of the foresight~~e.seen in line. N ow turn the rule round until the':,cslred bearing can be read through the prism, andf1amp. the upper plate. This fixes the line of fire. Bythosenmg the lower screw and laying on an aiming pointi. e angle from A to T is obtained. Knowing the(lrection of the Target one has merely to look to A,and angles left will be to targetB on the left, and viceversa. Or, the Director itself indicates whether theangle .is right or left. ('Vith No. 1 readings left of~{?wIll be left. 'Vith No.3" white is right," that is,ute letters on black enamel.)P b. The ahove result may also be obtained as follows.lace the angle given, right or left, on the Directorat once. Clamp the lower plate, loosen the upper.Place the prismatic compass on the sight rule so thatwhen seen through the prism the hair line on the lid ~>fi~hecompass, and the sight vane of the foresight are InIne. Now turn the sight rule until 3600 is read through

    =

    =

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    56the prism. The sight rule will then be' pointing ma,g-netic north. Clamp this line by mea,ns, of the upperscrew, remove the compass, loosen t,he lower plate, a,ndswing ba.ck to ze,ro to obtain tihe line of fire. By swing-ing from magnetic north directly on to an a,iming pointthe angle from A to T is obtained.(ii) With No.3 Director.-A trough compass is fitte~.See that the " notched" end of the oompass needle IS

    away from the eye piece of the telescope. Plaoe theangle given right or left on the director ,at once, andloosen the clamping lever. Turn the Director head untilthe needle is central, that is, pointing to magnetic north,and then clamp. Swing back to zero by pressing themicrometer head of the degree scale plate outwards.The telescope now gives the line of fire, which may bemarked by aiming posts, and individual lines of fire maybe given (see Section 11 of this chapter) or the a.nglefrom A to T may be obtained by swinging from magneticnorth directly on to an aiming point.NOTE.-Unless the teeth of the micrometer headare properly engaged with thOBe of the degreesca.le plate the la.tter is apt to slip. To preventthis, when placing an angle on the No.3 Directorit is well to put on a degree more (or less) thanthat required, making the exact adjustment bymeans of the micrometer head.

    (iii) 'Vith No. 4 Director. Unclamp the smalltrough compass as indicated on side of compass box, andproceed as with No.3 Director.

    8. To give Line of Fire with Compass from aDistant ObserVing Station from which BatteryIs not' Visible.(i) When Battery is on tile LEFT of OT.Take the bearing of T (a clocKw1'se angle always).Estimate the apex angle, and add it to t,he first he'a,ring

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    51

    X T

    y\ ,,\,

    F~!J.26 '\\ \ \\

    B

    NOTE.-If, as in Fig. 26, the bearing of T from 0is 3550, and apex angle BTO is 15, the sumwill be 3550 + 15 = 370, which is 10 right ofmagnetic north.o ~he angle ZOT, that is, magnetic bearing of T from

    , IS measured clockwise.

    ~

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    YB and TO are paraJIel.:. Clockwise angle XBY Clockwise a.ngle ZOT, a.ndapex angle BTO=angle YBT.:. Clockwise angle ZOT + Apex angle BTO Clockwiseangle XBY + angle YBT= a complet.e circle+ Bearing ofT from B.(ii) When B is on the RIGHT of OT

    yIII\ E'i!. 27\II

    Ta.ke the clockwise bea.ring of T from 0, a.nd from itdeduct the apex a.ngle. Gives bearing of T from B.NOTE.-Fig. 27, when apex angle is greater than bear-ing of T from O. The angle OTE the angle TBY.And angle ZOT angle XBY. Angle ZOT-angle OTn angle ZOT angle TRY.=angle ZOT- angle XBY -angle XBT.angle XBT.a negative angle, that is, lelt of

    ==

    ==

    = -= -=

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    59Put shortly, when the battery is on the Left of theohserver Add; when the battery is on the Right of the

    observer Deduct-LARD.9. Switches.. From a distant ohserving station, when 0 can 1300 B,It is gene,rally be,tter to m,asuretIle new ba.t.tery angle inthe ordinary way, and then the difference between thisne~ ba,ttery a,ngle and the old battery angle gives thesWItchangle.W"hen switchmg to a }lew tlir1ret which necessitates acl a' ,.., (h ldI nge 111 range, order parallellines.of fire on 1\ t eo.:arget) .before engaging'!' 2 (the new target). since the con-~elltra.tlOn or distribution required at one range is suitable

    rOf that range only. Then measure the necessary switchor a. flank gun and give all guns the same switch. ThegUllS will now be firing on '1'2 with p:uallellinea of fire, flndcOllcPlltration or distribution may be given as required.\Vhen both T 1 and T2 are marked on tho map it ismerely neoessary to measure with a protractor at B, thea,nglo from '1'1 to T2, to obtain the extent of the switch.

    10. To Measure Switch Angle when 0 can see Bwithout Re-plottlng Battery Angle.

    1.'he requireJ angle is '1\ BT2The observer measures the angle T 10'1'2 and calculatE's

    ~otl:, ~pex ltngles at T 1 and at '1'2' To obtain switch angle11,12 :-)' (i.) "If the new target ltlHl 0 are on the sflmt side of the

    ,:lIe lll\," that is. both to the right or both to the left,de1luet the old apex angle from the sum .of angle T 1OT~arid the new apex angle."(ii.) "If '1'2 and'O are on d~!ferent sides of the line BT~,

    "'}dd the old apex angle to the difference between T 1OT2 andt Ie. new apex nn~le."

    I

    -

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    \

    B

    60

    -72I!/1/ I/ I

    / I/ I/ I/ I/ I J:r0.28.

    / I/.l" II I/ II I

    I IoTo prove this consider the triangles T 1 nx and T20Xin Fig. 28.The angle T1XB angle T2XO.:. Angle T 1 + angle n = angle T2 + angle O.:. Angle B angle 0 + angle T2 angle T l'Again, if T2 and 0 are all opposite sides of TITI, thenangle T2 + angle B angle T 1 + angle O. Suppose theangles have these vallle8 T2 5, T 1 4, and 0 2.Then B (0 .:..T2) + T 1 (2 50) + 4= 3+ 4= 1.

    11. To Clve Individual Lines of Fire.(Often necessary-Aiming point not available, as on

    == -

    == = =

    == = - _

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    61(i) With No.1 Director.(a) Director in front of BaUery.

    f Having ~ot the direction of T (magnetic bearing givenCom the map) plant two ainlillg posts to fix this line of fire.8 arry the director forward from position D1 to position D2o to 100 yards in front of the battery. Lay on the aiming

    Dirl'ctiono/Target

    I II II II II II II I, I II I fig. 29I II II

    I aOtRCcrOP

    posts wi h director clamped at zero, 180 towards T, andiheu clamp the upper plate. With foresight next the ("!Ieay on the dial sight of No. 1 Gun, and then read off the~nglerecorded, Bay 25. If No.1 Gun is to the right of the.~le D2 and the aiming posts the angle will be 25 right.I o. 1 Gun will now place 25 right on dial sight, andfly on D2D The. angles for the remaining guns are gi ven similarly by

    2 laymg on the guns in turn.

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    62(b) Director in rear of Battery.

    Aiming posts are planterl as above. The directoris then taken from D1 to D3 clamped at zero, 180 towardsthe 'I' and laid al l the aiming JlOlStS. Clamp the top plate.Afir~Tl/orT

    With fores~q1Lt next the eye lay al l tIle dial l.iight of No.1Gnll and read the angle recorded, say 175. This will bothe angle for No. 1 (;un which will lay on DB"(ii) W"ith Directors fitted with telescopes looking fore-sight--backsight should be a.voided. The open s-ights ofthe No.3 Director give less accura,te resung, and naces.sitate the removal of the trough compass.Nos. 3 and 4. Directors.-The roade'r points to zero

    I

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    63

    \II,

    II

    III''''/,5 J1!'F' 31z:J

    Ail:?ing Posts, as in Fig. 29, laying over the posts in thelifdIna:y way (i.e., ba,cksight-foresight), adjusting forI no wIth lower clamping lever, or, thumb-screw. Noway on guns in turn, and the nece6Sary angles will borecorded.f To pIa,nt posts in rea,r (&ee Fig. 30), aft,er getting line1: fire, swing telescope through 1800 and plant poots inIne. Keeping reader a,t 1800 take Director beyondEOS1:s, a,nd lay o~ guns in turn. Angles required willo 1 ecorded on Dlrector.No'n.-If a gun is on the ri{Yht of the line of fire, asWa}rked l~y the j~imillg Posts, itO requires an angle righ~.b leu Director 18 in front of batter v a small ano(yle 18().t . uUlned. 'Vhen 10 rear the angle will he near 180012. To give Individual Lines of Fire with a Compass.

    (a) COMPASS IN FRONT OF BATTERY.'irectio71/ of" T

    310;\ API I I, ,: AP\ I

    ""

    ""

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    64NOTE.-To turn a forwa.rd be'8ring into a ba,ck bear-ing :-" (i) If forward bearing is le.s.~ than 1800 add

    1800 to it. (ii) If forwa.rd bearing is more than 180deduct 1800 from it." Thus a forward bearing of 20'"becomes 200'" when conve.rted into a ba,ck bearing i a,nd aforward bearing of 3400 becom8 a ba,ck bearing of160.Given the clockwise magnetic baring of T, aimingposts are planted to mark the line of fire. The R.C. then

    walks forward to the nea,rer post, about 100 ya,rds fromthe battery, and turns a,bout, that is, through 1800, sothat the forward bearing of T has now become a backbearing. He now lays on to the dial sights of the gunsin turn.The difference betwen the bea,rings of the guns andthe back baring of T will be the angles rquired. The

    guns will Ia.yon the nearer aiming post. If a gun is tothe right of the line marked by the posts, the a,ngle willbe right, and vice ver:sa.In Fig. 32, the forwa,rd hooring o,f T is 310 .. backbearing is 310 -180 = 1300Bearing of No.1 Gun is 115.

    :. Angle for No. 1 Gun is 1300 -115 15 right.NOTE.-Given bearing of T, 1900 ]\fagnetic.

    Back bearing of T= 190 -1800 10.Given bearing of No.1 Gun, 3550Difference 355 -100 = 345.Since the dial.sight is gradua,ted 1800 right and1800 left, take 3450 from 3600 and ord'r 15.(b) CoMPASS IN REAR OFBATTERY.

    Given the clockwise baring of T from magnetic north,plant aiming posta if desired. Walk aborut 100yards to the rear of the battery and look towa,rds thebattery. There is no neCoC'ssityet to introduce a back

    ==

    =

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    65~a.ke t,he bearing of the dial sight of No. 1 Gun and find

    '6 dZ,lference between this ba,ring and that of theD irectlQI'V or T

    fi#

    fi:J.32.00 -1I, :~:'ll

    \. N? 1CurC/

    target. Since No. 1 Gun will lay on B.C.'s compass (ora post ma,rking its position), that is, in an oppositeA.M.n. F

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    66

    direction to that of the target, the back 'bearing is hereinvolved. Consequently the angle required for No. 1Gun will be the difference between 180 and the differ.enoo a.Iready found a,bove.In Fig. 32. Bearing of T 10 magnetic and bearingof No.1 Gun= 25.

    Difference 15.:. Angle for No.1 Gun= 180 _15 1650and since tllis gun is on the right of the line of poststhe angle is 165 right.

    NOTE.-Given bearing of T, 350 Ma,gnetic.Bearing of No.1 Gun, 5 Magnetic.Difference 345.

    :.Angle for No.1 Gun=345-1800=165.

    ==

    =

    =

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    67

    CHAPT'E,R XIII.APEX OR DISPLACEMENT ANCLES.

    II A person standing at GI measures the angle AGI Te mOvesto G4, and measures the angle AG4,T.l'here will be a difference between the two angles measuredand the difference will be equal to the angle at T.

    "

    z:... on-!~ 1:J. J-J.

    :/}-----

    w' Tl~eexterior angle AGI T is equal to the sum of the anglesItllIn the triangle at T and G4,'i.e" Angle AGIT==allgle T+angle G,:. Angle AUI'!' angle G' ==angle T.

    l'his angle at T is known 1l,S the displacement ang-Ie orapex angle. J t is an angle aubtended by the line GIG,.-

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    68Now replace the letters used in Fig. 33 by TOB, andFig. 34 may be considered, where T is the target, B thebattery, and 0 an observe,r who can see II and T. .Aknoll lies between Band T. Now a is required to givethe battery the battery angle TBa. By referring toChap. XII., section 3, it will be Su tha,t the baUery

    angle TBa is equal to the exterior angle T'OX, lessthe apex angle at T which must be calcula,ted.

    x----If the angle TOB is from 800 to 1000 , tha,t is roughlya right angle, the triangle may be considered as a roughtriangle of reference, and the formulru

    D=H x 60B.may be employed to find the angle a,t T. The line BOcorresponds to II, the vertical height of the triangle of

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    70(2) If flag is 25 yards to rear of B, then angle BoFdivided into TO o of 25, that is 15 gives the line BO inhundreds of yards. BOF 3 then II 5 hundreds 500yards.

    3. To Find a True Working Base.If the angle TOB is not from 80 to 100, a workingbase must be found. (;/",.-.,IT~For as many tens of degrees that the angle TOB falls

    belo~, 80; or exce-eds)O.OQ,deduct tenths from the li~eBO. Thus if DO is' 500 ya,rds and the angle TOB IS130, the working base (by which to caIeula,te the a,pex.angle) will be 500 yardi less llr of 500, since the angle130 exceeds 100 by 30. T'his leaves jTTr of 500 yards,or 350 yards. .An alternative method of finding this working ba.se ISas follows:-

    (1) 'Vhen angle TaB elXceeds100.Given base DO=500 yds. a,nd T'OB=130.Strike off the cipher, leaving 13. Then talke13 from 20, le,aving 7. The working bas'ewill be-10 of BO, tha,t is, 350 yds.

    (2) 'Vhen angle TOB is less than 80 ;Given DO is 400 yds. and TOB is 60.Strike off cipher, lea,ving 6. Add 2.Thus the working base is 1.8~ of 400 yds.= 320 yds.

    Fg 3G 0Fig. 36 shows (a) Triangle TOB with angle TOB 60.'Vorking hase OX=,;. of BO. .(b) Triangle TaDI' with angle. TOBI 120. Workingbase OX 1.~~ of Bt O.

    ------------~--

    =- == =

    ==

    ==

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    71

    CHAPTER XIV.PARALLELISM.

    It is of grea,t importance that no overlapping should,f.ccur when a ha,ttery is firing on an allotted front. ThellI~es of fire of the ha,ttery should be parallel when firstaId out. '1. A. P. In Line of Cuns.I.If an aiming p:oint. be selected in p~olongation of. theIno of guns as III FIg. 37, parallel hnes of fire wIll be

    T

    Fig3?

    .A.I?

    oht,ained by giving the a,ngle from A. P. to T for eachgun, and no distribution or concentration is necessary.2. A. P. In Front .. \Vhen A. P. is in front of the battery, the lines of

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    72fire tend to oonverge as shown in Fig. 38, and distr,i.bution must be ordered to counterad this tendency, andto open out the lines of fire and make them pa,raHeI.

    LrZr,,I,

    Z:l,I,,

    IIIIII,

    I,,II '---

    z,,,,,,,, ,I I, ,, I, I, I, -r-:..-; -- ..-~..>-

    Fig. 38.

    GI and G2 are positions of Nos. 1 and 2 guns. L1 andL2, lines of fire required by these guns.Let AGI LI and AG2Z he equal angles from an aimingpoint.The angle AXLI ili greater than AGI Lu and thereforegreater than the angle AG2Z. COllsequently the lines GILland G2Z will tend to converge as they approach the target,and distribution (that is to the line G2L2) wiII be required toobtain parallel lines of tire.

    3. A. P. In Rear.'Vhen A. P. is in rear of ba,ttery t,he lines offire tendto diverge, and concentrat1:on must be ordered.If in Fig. 39 the same angles from A.P., AGI Lll andAG2Z are taken for NOH. 1 and 2 guns, the angle XO I A wiIIbe greater than the interior and opposite angle XG

    2A.

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    73

    .'r

    Fig. 3D.

    I;,.,~ \~ .., Z ,,

    \ I\, \\ \\ \\, ,

    \\ ICJ ~i-11'~2-l .~.","- ... ::::::-- - ... - .....--::-=--~::-:::...."-~-=-~~::::~"'':::-_::::'~""""--.4.PTherefore the angle XGl Ll will be less than the angle~G2Z. That is, the line G2Z teuds to diverge from thehne G L1 l'

    4. To Estimate Distribution or Concentration.The triangle AG1G4 may be considered as a TOB trianglewhere the angle at A.P. is a displacement or apex angle, sub-tended by the battery at the A.P. This apex angle may be

    -----A.P

    \

    \

    \\

    -

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    15In the example above a=lO and 2x=20.No.2 gun 20 yards from No l~ 10', ~x ~O

    more left.No 3 gun, 60 yards from No. l~ =~=30'~x 20more left.No.4 gun, 90 yards from 'No. l-~ =~=45':.!X :.!O

    more left.An Aiming Point should be as fine as poosible-eo

    nsequently, the farther from t,he battery the better.

    '=~ =

    -

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    77A front of 75 yards will measure = ~ of this, that. 100 4

    Is, ! of 2 10 30'.1. To find Distribution or Concentration.EOCAMPLE 1.T A .4-gun battery (20 ya,rds intervals) is to cover a, wIdth 3, and range 3,000 yards.The battery should lay within both the margins ofthe T to the extent of k of the width of the T. Thust should be deducted from the 3, leaving! of 3 21b 135' to be oovered. \Vith parallel lines of fire theattery will cover

    60 x 60 72'.It 3,000

    E that 135' -72' 63' must be covered by distribution.,a?h gun will have to distribute to the extent of 63'diVided. by 3-gun intervals, that is 6di =:H' from thenamed gun.EXAMPLE 2.A 4-gun battery (25 yards intervals) has to cover 10

    at 3,000 yards range.th 100 yards front at 3,000 yards measures 4 2, soat 75 yards front measures -ll~ of 2=1!0=90fT to be oovered, allowing k off at each end i of 10==45', so that the 'guns must concentrate 90-45=45'.l'hu8 each gUll mllst ('O IJ(:('lltrate \" U)' Oil thenamed gun.2. Constant 72. Field Artillery.For gun inteJrVals of 20 yards.

    EXAMPLE 3.o A 4-gun battery (20 yards intervals) has to cover T of4 at 5,000 yards.

    ~=

    =

    ~= ==

    ==

    =

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    A

    78Bule.-Divide T in minutes by the number of guns,

    and deduct 72 divided by the number of thousands ofyards in R. This gives minutes, distribution, or con-centration.240 72Thus 60 15 45' distribution.4 5

    EXAMPLE 4.A 4-gun battery (20 yards intervals) is to enga,ge asingle enemy gun, range 3,000 ya,rds.Find concentration.In this case width of T can be taken as nil.

    Then Q 72 24'. Order 2:5'concentration.4 3N.B.-A positive answer, as in Example 3, mea,nadistribution, and a negative answell", as in Example 4,means concentration.

    Beason for the use of Constant 72.Let A = a,ngle in degrees covered by Z guns (a,t 20yards intervals) and 'y' the number of thousa,nds ofyards in range.There are Z -1 intervals of 20 ya,rda.i.e" Z 1 hundreds of yards.

    5Z-lx6-5-' 6(Z-l)

    Y 5,).Let X = width of target.

    - - - = - =

    -= -

    -

    ~

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    79Amount to distribute = X AZ

    X )60 (X-:z-AZ-l mins.

    Substituting value of A-_60X(y)Z-l

    60(Z-1)65 Y (Z 1)

    60 X 72=-Z- YIt will he ohserved that the full target width ispla,oed over the number of guns. The formula makesallowance for the eiO'hth within the flanks of the targettha,t the guns are laid. and for what the guns cover with

    paranel lines of fire.3. Constant 90. Heavy Artillery.For g~n intervals of 25 yards.Rule.-Divido T in minutes by the numoor of gUllSand deduct 90 divIded by the numhcr of thousands of

    yards in range. This gives minutes distribution or con-centration.EXAMPLE 5.A 4-gun battery (25 yards intervals) has to cover a

    front of 50 a;t 5,000 yards range.300 90 75 18 57'4 5

    Order 55' distribution.

    - ~ -

    - -

    -

    _ _ =

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    80The reason fur this constant may be shown as in the

    proof of Constant 72.4. Varied Cun Intervals.(i) Regular Intervals other than 20 yards and 25yards.

    . . 7 New IntervalObtam a new constant by multIplymg 2 by --')-0--'90 b New Interval ...or y 25 .A 4-gun battery intervals 30 yards. Give necessary dis-tribution to' cover a 4 target at 3,000 yards.(a) Constant is 72 x 30 (or 90 x 30) 108.20 25Then 240 108 60 36 24' distribution.4 3Or (h). After deducting .~ from either eud target 3.'Vith parallel lines the battery covers 90 yards llJOoiY of100 yards at 3,000 yards -t'rJ of 2 ="~ 1 48'. 'rhis leaves3 1 48' 1 12' to be covered by distribution. Dividing1 12' by 3 (gun intervals) distribution required is 24'.(ii) Irregular Intervals.A 4-gun battery has obtained parallel lines of firewith No.1 gun on a 20 ta.rget a,t 3,600 ya,rds. Int,erva.ls-Nos. 1-2, 20 yds.; Nos. 2-3, 40 ydSl.; Nos. 3-4,50 yds. Distribute the fire equaHy over the ta,rge1tfront.Conve,rt the target width into yards.

    H D x It 2 x 3,600 120 i(the target in yards) 60- 60 yart s.No. 1 gun has laid .~ within the target fla.nk. If thefire is to be eqnally distributed the shells mnst fall

    Target = ~ 30 yards apart.

    =_ = _ =

    ==

    =- =

    = = -

    =

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    81With parallel lines of fire, No. 2 gun would drop a~ehell 20 yards from that of No.1, and therefore requires

    ee 10, yaros" more left. To convert this into minutes,olrtng the diff~rence. to inches and divide by the hundredsyards in the range." N 10 x 36 I I fo. 2 36= 10 more e t.

    :N".:N"o. 3 gun. sihould strike the t~get 2 x 30 yards fr?m:N"o. 1, and IS thus correct for hne when parallel wIth0'. 1 gun.

    No.4 gun (110 90) x 36 20' . ht---36---= more rIg .5. Sweeping.t' Sweeping is adopted when T cannot be covered effecIvely by distribution.th ~ach gun has t of T allotted to it, which is taken ah lrd a,t a time; tha,t is, y12 of T in degrees for eachS .ell, or ee 5 times T in degrees = amount of sweep inInlllutes, for a 4-gun hattery"; "10 times T in degrees::::amount of sweep in minutes for a section."

    II M II Q

    -

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    82

    CHAPTER XVI.FOREleN CONVENTIONAL SleNS.

    RAILWAYS:-Chemin de fer

    !~.n.np'

    K3 3 Kllometrea from termlnu8

    ROADS

    ~oute Nat/onal.Route lie Menln

    1~~\:84~B4 1st Class Road.r,. p~, ""-"'-. ........,.,. 8 'NIt" .P.C!CZ':_s.uJ1.ace-........... ..~ ....... ... ... .B4, B".4, B4. Borne 4 4 kllometre. 'rom

    nearest town.Borne -limIt, boundary atone kllom ..tr" stone

    orCt.Engllsh milestone .

    "::=:~, ~I~=+=I =+:1=+:1~IHI=+=I::;IHI=+='~Ii=;.Road. wIth TramwaYli

    Boutldar1ea.

    /I :or + + + + + +

    -

    -

    -- _

    _

    ~

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    83

    RIVERS

    .. g.... Hale.g o . o ... oHOtl

    "Ulftlllllllll.~araia. ""111'""11" Ma

    ttllttlllltfHl" MarshII11I//i1/WIII

    o 2

    ~

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    84BUILDINGS, E'l'c

    L Cabt Cabaret J Inn (commonly knownAubge Auberge I as Estaminet).,..--- ....,:1..1: Ch&u, Chateau Country House (large).. ....... -'.--. - ... -o. ~.-r Fme. Ferme Farm._____..:..I.,

    Tie. Tuilerie Tile Kiln.,.J Briqie. Briqueterie Brickfield.

    As shown in towns.

    Gas Works.Foundry.Paper Factory.Hefinery.Sugar Works.Glass VV orks.Powder Works.

    A 'Vayside Shrine.Chapel or Church.

    Usine 'Yorks, manu-factory.Usine-a. gflZFrie. FonderieI>apie PapeterieHafle.. RaffinerieSuc'e. SucrerieVie. VerreriePoudie. PoudriereBrasserie Brewery.Huilerie Oil Factory.Eglise Church

    Croi x or Cal vaireChap)'" ChapelJeo(5+Mn. Moulin

    (or Molen)Moulin it eallScieric'Moulin a. vent

    :Mil!.Watermill.Sawmill.'Vindmill.

    o I>uits 'VeIl or Shaft.Sablonniore

    ro.Sand Pit, Gravel Pit

    -

    ~... _ ...

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    87If an angle be made hy two lines running from thecentre bottom of the paper to the ends 0. the eye line(horizon) of the sketch, and measured, another means

    of checking the a,ccuracy of reference poin.ts is obtain~.~easure this angle, and note how many tImes greater ItIS tha,~ the angular width of the view. Say ~ve. .Th~nan otbJed, that is 6 from the left of the VIeWWIll heon a line 5 x 6, tha,t is, 30 from the line joining thecent.re bottom and the left of the eye line of the sketch.4. Having estahlished several reference points other

    prominent points ma~ be inserted. Leave detail untillash.Finishing the Sketch . 1. Hedges give a good impression of the shape ofhIlls .. ~. 'York very lightly-a rubber should not be usedIf It can be possibly avoided. It is easy to add lines.h 3.. Do not show much detail when depicting trees,ooUses,et,c. Impressions are required. The foreground~~olUld be bold and dark, the distance faint andsketchy."

    The Marginal Notes. 1. Below the sketch make a plan of the countryV'I6';6d. Insert your pooition on the plan, as well asstatmg it according to the squares on the map, and inserta north line .. 2. Above, point out and name prominent points, giv-Ing ranges and magnetic hearings.Possible targets--possible battery po:;itions and ob-ser~a~ion stations, cross roads, railway junctions; largebUIldmgs are important ..NOTE.-To prevent smudging, the sketch mAy besprayed with a solution of shellac.

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    88

    CHAPTER XVIII.TECHNICAL TERMS.1. :MAP READING.

    The refNences are to the map, a,nd the example,s givenshould be carefully studied so that a contoured map may,after a short time, give a.s clea,r an impression of hillfeatures as a carefully made relief.Basin.-A small area of fairly level country sur-rounded, or nearly surrounded, by higher ground. Thearea drained by a river and its tributa,ries is known as ariver basin.Base.-A carefully la,id down starrting line, or refer-ence line, of a sket.ch. The lowest port,ion, or foot, ofa mountain. ,Bearing.-(a) Alagnetic Bearing.-The angle madeby a line drawn towards magnetic north, and a linedrawn from the centre of the compass towa,rds a distantobject. .(h) True Bearing.-The angle between a true northline and a line drawn to a distant object.Back RaY.-A line drawn from a dista,nt pointtowards one's position.Brow.-See Crest.BluH.-See Spur.Cardinal PointS.-The four principal points of thecompa,ss--Norlh , South, East, 'Vest.Contour.-A line of level, any point on which is 'thesame vertical height above datum level.Crest.-The summit, or highe,st point of a hill. Thepoint at which a steep ascent changes to a gentle one.

    B.12. b.4. 7; E.8.b.0.4.

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    89Col.-A neck of ground connecting two heights .. A 'pa,rtia,}break in a ridge. From a col the ground rIses

    on two sides and falls on the other two sides.A.15.c.6.9.Datum Level.-The level (not necessarily sea level)

    from which all heights are reckoned.Defile.-Anything tha,t necessitates a reduction offront. Narrow valleys, gorges, bridges, fords, roads

    a,crossswamps, streets, etc.Forward Ray.-A line drawn from one's position toa distant point.Cradient.-A slope expressed as a fraction. Thus-lIT ~ean3 a rise (or fall) of 1 foot in 10 feet measuredhOrIzontally; or 1 metre in 10 metres. This gradient

    . would he spoken of a,s1 in 10. (See Chap. VII.)Hachuring.-A method of shading hill features by

    dra,wingshort lines velitical to, or horizontal to contours.Horizontal Equivalent (H. E.).-The horizontal dis-tance in which a given rise or fall will occur at a givendegree of slope. (800 Chap. V.)

    Intersection.-See Triangulation.Knoll.-A small eminence or hillock. A.15.c.

    SMeridian-or True Meridfan.-A true North andouth line.

    1. Magnetic Meridian.-A magnetic North and Southme.North Point.-A diagram on every military sketch tos~ow the true and magnetic meridians of the sketch

    WIth the variation.Or.ienting-or Setting-a Map.-Placing it in ita

    relatIve. position to the country it represent8. LinesCo~nectlllg positions on the map will be parallel to orCTolllcidewith the lines they represent on the ground.he compass needle will coincide with the magneticmeridian on the map.Plateau.-An elevated plain.

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    90PlotUng.-Laying on paper measurements and bear-ings taken in the field.Points of the Compass.-The 32 points of the oom-pass card. N.E., N., N.W., etc.Ravine.-A deep hollow or narrow valley, generallyformed by the action of a stream. Often described asa gorge or mountain cleft.Re-entrant.-A wateroourse or valley between twoprojecting portions of a hill.A.8.d.9.0. running \Vest,.A.3.d.7.0. running South.Ray.-A straight line representing an imaginary lineconnecting two foints in the field.Representative Fraction (R. F.).-A fradion show-ing the proportion between the map and the ground itrepresents. (S.eo Chap. IV.)Resection.-The method of locating one's positionon a map by the intersection of ba,ck rays. (Soo Chap.XI.) .Saddle.-A col.Salient or Spur.-A projecting port,ion of a hill orridge. A.3.d.3.0 running \Vest.Section.-The outlino of a hill as it would appea,r ifcut away vortically. (See Chap. VI.)Setting a map.-See orinting.Triangulation.-Fixing forward positions by theintersection of forward rays.Triangle of Reference.-A right-angld tria,ngle.perpendicular height 1 yard, opposite angle 10 a,nd base57'3 yards. (See Chap. VII.)Triangle of Error.-The triangle formd when a,nyinaccuracy occurs in the drawing of tho three back rays

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    93~?rtical movement of the gun on firing, and, for any gun,lifers acoording to the mounting and the charge used.. Lateral Deviation.-The dist.ance of the point ofIlllpad of the projectile right or left of the line of fire.1 Li.ne of Departure.-The direction of the shell oneavmg the muzzle.Line of Fire.-A line joining the muzzle of the pieceand the t,a,rget.. Line of Sight.-A straight line passing through theSIghts and the point aimed a,t..Muzzle Velocity.-The velocity in feet per secondwIth which a shell leaves the muzzle.t Normal.-A line at right~angles to the fr~:>Dtf thearge,t. In the case of a cIrcle a prolongation of theradius,I' Point Blank.-A gun is laid point blank when theIne of sight is pa.rallel to its axis .. Quadrant Angle.-The angle which the axis of thepIece makes with the horizontal plane. It is termedf'~adrant eleva,tion or depression according as the gun istJ.d ahove or below the horizontal plane. It is, there-o'1'e,the sum or difference of the angle of elevation:nd t~e angle of sight (see Fig. 41). The angle ofl'Ie,va,tl0nand the quadrant angle are the same when theme of sight is horizontal.th Ranl:?e.-The distance to the second intersection ofe tra'Jeetory with the line of sight.~anging.-Ranging is the process of finding the ele-

    va,hon, fuse and line., Remaining Veloclty.-The velocity of a shell at anygIVenpoint of its trajectory.~triking Velocity.-The velocity of a shell at thePOInt 0' impact.fl' Trajectory.-The curve descri~ by the shell in itsIght. (See Fig. 42.)

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    94

    CHAPTEH XIX.NOTES AND RULES.-AIDS TORECONNAISSANCE.

    Accommodation.IIoRsEs.-Allow 2 yards of frontage for each horse.

    lf more than one row of animaJs are to bo accommodated,the shed must be a.t least 8 yards wide.PARKINGVEHICLEs.-Leave the following spaces infront of vehicles or guns:-Heavy Gun, 16 yards.6-Horse Vehicle, 12 yards.4-IIorse Vehicle, 8 yards.I-Horso or 2-Horse Vehicle, 5 yards.

    BRIDGES.-8 feet wide will suffice for infa,ntry in foursor cavalry in half sectJons; 6 feet for infant.ry in file,cava