When you're looking for the right potentiometer to doa specific job, it will pay you to check the completeL&N line first. Whether you need the extreme precisionof an N.B.S.-certified Wenner, the convenience of aMicromax or Speedomax recorder, or an intermediateinstrument, you'll find the characteristics you want in asoundly engineered L&N potentiometer.More than a score of models comprise the line. Just

glance at the table below. There's a potentiometer for,practically any of low voltages,

temperature vs. temperature-difference, calorimetry, pHand other emf cell work ... self-contained portables fortemperature and pyrometer checking ... and the popular,general-purpose Type K's. Models run from highest tomoderate precision. They come in convenient single,double, even triple ranges. to suit the job at hand.

Naturally, we can't begin to tell you all you wantto know in so short a table. So for complete details, letus send you catalog information. Simply write our nearestoffice, or 4926 Stenton Ave., Phila. 44, Pa.

_______CAT ________-|LIMIT OF ERRORt R NNO.

.01%0 .2 1~|MODEL | N o .|PUoRPOSE E Ian _ _

Wenner 7559 thermocouple; other low voltages x OtoO.011111 v; OtoO.11111 v(N.B.S.-certlfled) 7558 maintain primary standards x OtoO.19111 v;Oto 1.9111 v

(Single)(f7620 thermocouple voltages; calorimetry xOto 0.01 v

White7621 thermocouple voltages; calorimetry x O to 0.1 v7622 temp; temp-difference; x Oto 0.01 v

(Double)1 7623 temp-current; etc.. x Oto O.1 v

Type K-1 7551 general x O to 0.161 v;O to 1.61 v

Type K-2 7552 general x OtoO.0l61 v;OtoQ.161 v;Oto 1.61 v

Students' 7651 general x 0 to 0416 v; Oto 1.6 vIndicator * 7655 pH, emf's x Oto 1.110 v

* 7659 corrosion testing x triple;O to 4.1 v total

Millivolt * 8667 pyrometer check (lab.); temp. x Oto 111 mv

Indicator * 8656 B,D,X pyrometer check (plant); temp. x 0 to 16 mv; 0 to 70 mv; or as spec.* 8657 pyrometer check (plant); temp. x Oto 16 mv & 16 to 64 mv; or as spec.

8662 pyrom. check (lab. & plant); temp. x 0 to 16.1 mv; 0 to 80.5 mv

* 8658 pyrom. check (lab. & plant); temp. x single; direct-reading temp.

Temperature * 8659 pyrom. check (lab. & plant); temp. x double; direct-reading temp.Indicator * 8663-CD body temps. x 25 to 125 F;-3.9 to +51.7 C

8663-X temp. check (lab. or plant) x single or double, as spec.Panel Indicator a 8671-76 temp. meas. x single.or double, as spec.pH Indicator * 7663-Al pH; emf cell potentials | x Oto 13 pH;O to 1.100 v

Brooks 7630 ammeter, voltmeter, wattmeter test. x 0 to 153 mv lused with volt boxes(Deflection) 7640 lamp efficiency test. x 0 to 1.53v and shuntsMlcromax ax as spec.M__icromax_____ automatic indicating, recording x asspeG

Speedomax a controlling: voltage, taMp., PH, etc. x as spec.

*Self-contained runder normal operating conditions, except when using lowest part of ranges

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Features of the new edition: concepts of pathologic physiology are integratedinto all discussions; 20 new subjects are covered (collagen diseases, Q fever, etc.)and 82 discussions have been completely rewritten.Edited By RUSSELL L. CECIL, M.D., Professor of Clinical Medicine Emeritus, Cornell University; andROBERT F. LOEB, M.D., Bard Professor of MIedicine, Columbia University. Associate Editors: ALEX-ANDER B. GUTMAN, M.D., Professor of Medicine, Columbia University; WALSH MCDERMOTT, M.D., Asso-ciate Professor of Medicine, Cornell University; and HAROLD G. WOLFF, M.D., Professor of Medicine(Neurology), Cornell University. 1627 pages, 7" x 10", with hundreds of illustrations, some incolor. $12.00. New (8th) Edition.

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Hilton HIGH-SPEED AERODYNAMICSBy W. F. Hilton, Armstrong Whitworth Aircraft, Ltd., Coventry; formerlyof The Johns Hopkins Applied Physics Laboratory. April 1951. 608 pages.394 figures. 24 half-tones. $8.50. Conditions of flight just below, through,and above the.speed of sound; the physical laws and mathematical analysisof high-speed flight; and the design of high-speed planes and rockets andtheir motors.

Lang SOME ASPECTS OF FLUID FLOWEdited by H. R. Lang, Secretary and Editor of the Institute of Physics,London. Ready, June 1951. 296 pages. 112 figures. Tables and bibliographies.About $8.00. Papers presented at the Institute conference of October 1950,with reports of discussions; covers fundamental problems, techniques, andapplications of present knowledge and techniques.

Alexander SURFACE CHEMISTRYBy A. E. Alexander, New South Wales University of Technology. Ready,July 1951. About 85 pages. Figures and half-tones. About $1.50. Historicaldevelopment, insoluble monolayers, adsorbed films, the gas-solid interface,the solid-liquid interface, and electrical phenomena at interfaces.

Reddaway THE REBUILDING OF LONDONAFTER THE GREAT FIRE

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Havighurst SOCIAL HISTORY OF A& Morgan WAR-BOOM COMMUNITY

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SCIENCE, Vol. 113a

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TAXONOMY OF VASCULAR PLANTSby Lawrence

It is believed this book will be the most complete andauthoritative text on plant taxonomy that has been pub-lished in the English language. It provides in one volumea comprehensive source of information on the theory,principles, and operating procedures followed in planttaxonomy plus an accounting of all of the families ofplants known to grow in North America. Ready forfall classes.

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FOUNDATIONS OF BIOLOGY, 7th Ed.by Woodruff and Baitsell

Very careful attention has been given throughout thenew edition to the complete integration of the textualmaterial so as to make a logical, coordinated and con-tinuous story of biology. Important new material hasbeen added and long chapters have been split to makefor increased student interest and more adaptable as-signments. The complete assembly of illustrations inthis new edition are believed to be superior to that inany previous edition. Coming in June.

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XhSs-&StS Vol .

SCIENCE, VOl. 11310