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THE BROOKS' INDUCTOMETER

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In the Brooks' Inductometer is offered a compact form of variable inductance, with a self inductance range of 5 to 50 millihenrys, possessing the following advantages:

1. A fair degree of astaticism, which tends to eliminate errors due to stray field effects.

2. It is less expensive and at the same time fully as accurate as the AyrtonPerry instrument.

3. It occupies less space than the

Aryton-Perry form. The instrument has a very nearly uniform scale, obtained by properly proportioning the coils. It may be used as a mutual inductance.

It has a good ratio of maximum to minimum inductance (about 9 to 1) and also has as high a time constant as is consistent with good design and moderate size.

The instrument is fully described in Bulletin No. 152, a copy of which will be sent upon request.

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THE LEEDS & NORTHRUP CO.

ELECTRICAL MEASURING INSTRUMENTS 4921 STENTON AVENUE

PHILADELPHIA

Natural History Material

Naturalists' Supplies

We carry a stock for prompt delivery

ZOOLOGY MINERALOGY

We have been handling Natural History
Material of all kinds for the past fifty years,
and so have accumulated a very complete
stock. Our prices are as low as the quality
of the specimens will permit. We are con-
stantly preparing circulars and price lists
covering our material in the different branches,
which we will be pleased to send free of
charge to the readers of Science.
Some of our recent circulars :

S-121 Rare Bird Skins
S-122 Mounted Bird Skins
S-98 Materialfor Dissection
S-123 Philippine Land Shells
S-120 Special Minerals
S-110 Complete Trilobites
S-111 Jurassic Fossils

S-119 Cretaceous Fossils
CONCHOLOGY

I. Collecting Utensils.
II. Breeding Apparatus and Cages for Living

Animals.
III. Preparing and Preserving Utensils.
IV. Cabinets and Insect Cases.

V. Magnifiers, Microscopes and Accessories.
VI. Botanists' Supplies.
VII. Explorers' and Collectors' Camp Outfits.
VIUI. Miscellaneous Naturalists' Supplies.
IX. Oologists' Supplies.

X. Aquaria.
XI. Books and Publications.
XII. Chemicals

K-S Museum Cabinets of Glass and Metal
Catalogue, Circular or Information on application

GEOLOGY

THE KNY-SCHEERER CORPORATION

Ward's Natural Science

Establishment College Ave. Rochester, N. Y.

Dept. of Natural Science

G. Lagai, Ph.D.

404-410 W. 27th St

New York City

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AMERICAN STANDARD

HAEMACYTOMETERS

WITH LEVY COUNTING CHAMBER

The Levy Counting Chamber was announced in November, 1916, patented January 31, 1917 (U. S. Patent No. 1,214,331) and awarded the Edward Longstreth Medal of Merit by

the Franklin Institute, Philadelphia, December, 1917.

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WAR SERVICE During the war 4,064 AMERICAN STANDARD HAEMACYTOMETERS with Levy Counting Chamber with Neubauer ruling were supplied the U. S. Army Medical Department, in addition to 1,100 separate Levy Counting Chambers with Fuchs-Rosenthal ruling for spinal Auid investiga tions. At the time of the armistice there were undelivered 1,700 complete American Standard Haemacytometers with Levy Counting Chamber on our contracts, for which we accepted cancellation.

IMPORTANCE OF BUREAU OF STANDARDS CERTIFICATION We emphasize the importance of using Haemacytometers with Bureau of Standards certificate for both counting chambers and pipettes, as many Haemacytometers in use are so inaccurateparticularly as to depth of chamber—as to largely invalidate the result of counts. Exact measurement in the clinical laboratory of either ruling or depth of chamber is difficult, and where precise blood counts are desired the use of a certified Haemacytometer is clearly indicated.

The Levy Counting Chamber, since its first announcement, has been regularly stocked by us with Bureau of Standards certificate, and the tolerances published by the Bureau were established at our request.

ARTHUR H. THOMAS COMPANY

IMPORTERS - DEALERS - EXPORTERS LABORATORY APPARATUS AND REAGENTS WEST WASHINGTON SQUARE

PHILADELPHIA, U, S. A.

SCIENCE

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THE MEASUREMENT AND UTILIZATION OF BRAIN POWER IN

THE ARMY1 History of Psychological Service.--The psychologists of America, of whom upward of two hundred served in the Army or Navy, have rendered conspicuously important assistance to the government in organizing an efficient fighting machine. Chief among the civilian agencies responsible for the development of this new and unexpectedly significant variety of service are the American Psychological Association and the Psychology Committee of the National Research Council. Nearly a score of committees or subcommittees of these organizations functioned during the military emergency

Within the Army three principal groups of psychologists appear: one attached to the Office of The Adjutant General of the Army (specifically known as the Committee on Classification of Personnel in the Army), another in the Office of the Surgeon General of the Army (known as the Division of Psychology of the Medical Department), and a third in the Division of Military Aeronautics (the Psychological Section of the Medical Research Board). Although the several tasks of these groups of psychologists differed markedly, the primary purpose of each was the increase of military efficiency through improved placement with respect alike to occupational and mental classifications.

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1 Published with the approval of the SurgeonGeneral of the Army, from the Section of Psychol. ogy, Office of the Surgeon-General, Major Robert M. Yerkes, Chief.

Psychological service was rendered also skeptical concerning the practical values of to the following divisions or departments in psychological service and inclined to anticiaddition to those named above: (1) the pate research instead of service, shortly Morale Branch of the General Staff, (2) achieved a new point of view and opinion. the Division of Military Intelligence, (3) Skepticism was replaced in some directions the Committee on Education and Special gradually, elsewhere rapidly, by faith in Training of the War Department, and (4) the practicability and immediate value of the Chemical Warfare Service.?

various kinds of psychological work and Early in the emergency it became clear eagerness for its continuation and extento psychologists in the military service that sion. In the end the psychological personthe fundamental psychological problem of nel of the army was completely swamped by the army is one of placement and that the requests, demands and orders for help. most important service psychologists could Scores of telegrams and letters from compossibly render would be to assist in so as- manding officers testify to their hearty apsigning every soldier that his mental (as preciation of efforts towards scientific well as physical) ability should be used to placement within the army and their desire advantage. It was assumed by the psycho- for the introduction or furtherance of logical personnel that intelligence, alertness, psychological service in various departthe will to win, enthusiasm, faith, courage ments or organizations. and leadership are even more important Skeptics, of course, still exist and there than are physical strength and endurance, are inevitable misunderstandings and preand that this fact must be scientifically judices, but the data at hand indicate that reckoned with wherever a strong military at least seventy-five per cent. of the officers organization is to be built quickly. Very of the United States Army have been won promptly it became the recognized purpose by actual demonstration of values and first of army psychologists to assist in winning hand acquaintance with psychological servthe war by the scientific utilization of brain ice to its hearty support. power. The achievement of this purpose It is extremely important to emphasize necessitated the preparation of special

at the outset that this article deals with methods of mental measurement in order only one of the several important lines of that recruits should be properly classified psychological military service, that, namely, for elimination or assignment to military of the Division of Psychology of the Medtraining.

ical Department. The army, at first naturally and wisely

Purposes of Mental Examining.- As

originally conceived, psychological service 2 For the United States Navy serviceable meth.

within the Medical Department was to asods of selecting, placing and training gunners, lis

sist medical officers, and especially neuroteners and lookouts were devised and developed by Lieutenant Commander Raymond Dodge.

psychiatric officers, in discovering and methods prepared by Dr. Dodge as well as certain eliminating men who are mentally unfit instruments designed by him for naval use have for military duty. It appeared, prior to been extensively and profitably used, and the ap- actual trial, that reasonably well planned pointment of this psychologist as Lieutenant Com

methods of mental measurement should mander in the Naval Reserve is at once a fitting recognition of his practical service and an indica

enable psychological examiners to discover tion of the appreciation of his work by the officers mentally inferior recruits as soon as they with whom he has been associated.

arrived in camp and to make suitable

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