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. 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 constantly 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-119 Cretaceous Fossils CONCHOLOGY GEOLOGY Ward's Natural Science Establishment Naturalists' Supplies We carry a stock for prompt delivery I. Collecting Utensils. II. Breeding Apparatus and Cages for Living III. Preparing and Preserving Utensils. V. Magnifiers, Microscopes and Accessories. VII. Explorers' and Collectors' Camp Outfits. X. Aquaria. XI. Books and Publications. K-S Museum Cabinets of Glass and Metal THE KNY-SCHEERER CORPORATION 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. 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 fluid 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 THE MEASUREMENT AND UTILIZA- 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. 1 Published with the approval of the SurgeonGeneral of the Army, from the Section of Psychology, Office of the Surgeon-General, Major Robert M. Yerkes, Chief. Psychological service was rendered also to the following divisions or departments in addition to those named above: (1) the Morale Branch of the General Staff, (2) the Division of Military Intelligence, (3) the Committee on Education and Special Training of the War Department, and (4) the Chemical Warfare Service.2 Early in the emergency it became clear to psychologists in the military service that the fundamental psychological problem of the army is one of placement and that the most important service psychologists could possibly render would be to assist in so assigning every soldier that his mental (as well as physical) ability should be used to advantage. It was assumed by the psychological personnel that intelligence, alertness, the will to win, enthusiasm, faith, courage and leadership are even more important than are physical strength and endurance, and that this fact must be scientifically reckoned with wherever a strong military organization is to be built quickly. Very promptly it became the recognized purpose of army psychologists to assist in winning the war by the scientific utilization of brain power. The achievement of this purpose necessitated the preparation of special methods of mental measurement in order that recruits should be properly classified for elimination or assignment to military training. The army, at first naturally and wisely 2 For the United States Navy serviceable methods of selecting, placing and training gunners, listeners and lookouts were devised and developed by Lieutenant Commander Raymond Dodge. The methods prepared by Dr. Dodge as well as certain instruments designed by him for naval use have been extensively and profitably used, and the appointment of this psychologist as Lieutenant Commander in the Naval Reserve is at once a fitting recognition of his practical service and an indication of the appreciation of his work by the officers with whom he has been associated. skeptical concerning the practical values of psychological service and inclined to anticipate research instead of service, shortly achieved a new point of view and opinion. Skepticism was replaced in some directions gradually, elsewhere rapidly, by faith in the practicability and immediate value of various kinds of psychological work and eagerness for its continuation and extension. In the end the psychological personnel of the army was completely swamped by requests, demands and orders for help. Scores of telegrams and letters from commanding officers testify to their hearty appreciation of efforts towards scientific placement within the army and their desire for the introduction or furtherance of psychological service in various departments or organizations. Skeptics, of course, still exist and there are inevitable misunderstandings and prejudices, but the data at hand indicate that at least seventy-five per cent. of the officers of the United States Army have been won by actual demonstration of values and first hand acquaintance with psychological service to its hearty support. It is extremely important to emphasize at the outset that this article deals with only one of the several important lines of psychological military service, that, namely, of the Division of Psychology of the Medical Department. Purposes of Mental Examining.-As originally conceived, psychological service within the Medical Department was to assist medical officers, and especially neuropsychiatric officers, in discovering and eliminating men who are mentally unfit for military duty. It appeared, prior to actual trial, that reasonably well planned methods of mental measurement should enable psychological examiners to discover mentally inferior recruits as soon as they arrived in camp and to make suitable |