D, which engages with the under surface of the table at R, the operator releases the table which starts to turn under the pull of the weight. The metal ring E to which the cord B is attached drops off the post C as the table completes about a quarter of a turn, i.e., as soon as weight A has come to rest at the base of the table. Although the amount of friction is reduced to a minimum, by reason of the fact that the axis of the table rests on a polished steel ball enclosed at S in a metal collar, it is still necessary to devise a means of keeping the rate of rotation constant after the initial impulse has been given to the table in the manner described. This is done by means of weight F which may be attached either at G or H depending on whether the direction of rotation is clockwise or counterclockwise. As cord I (or J) unwinds over the pulley K (or L) as the table revolves, the weight F falls and is just sufficient to overcome the frictional resistance of the axis of the table and thus keep the rate of rotation approximately constant. The weight of F is 193 grams. As weight F falls by reason of the unwinding of I, cord J winds around the axis of the table and H is pulled up to the pulley L. As it comes in contact with the pulley it pulls brake M into contact with the periphery of the revolving table at N, and thus stops the table. If weight F is attached at H, the other brake, O, is used. In this manner the table is halted without the interference of the operator and in a constant manner. The number of revolutions of the table is dependent upon the length of cords I and J. In the present instance they allow the table to make 10 revolutions. The rate of rotation is controlled by the mass of weight A and distance through which it falls. In our investigations the rate was 10 revolutions in 20 seconds. The weight of A was 2740 grams. The direction of rotation is dependent on whether weight A is attached by the metal ring E to post C or post P. Weight F is attached at G or H dependent upon the direction of rotation. The releasing devise D is duplicated on the opposite side of the table (not visible in the picture) at Q. D or is used depending on the direction of rotation. D and are, of course, stationary and are mounted on wooden 4 Fearing, F. S. Post-rotational head nystagmus in adult pigeons. J. Comp. Psychol., 1926, 5, No. 1. strips which project from the supporting platform to the periphery of the table. In order that the releasing device D may not interfere with the table when once it is set in motion, it pivots on an axis and is thus out of the way during the rotation of the table. The table was calibrated by means of electrical contacts made at each quarter revolution in circuit with an electric time-marker playing on a kymograph. These calibrations showed that the acceleration took place during the first quarter-turn, after which the time per turn remained relatively constant until the last quarter-turn, when the brake was applied. At the time of calibration, when the table was set for 10 revolutions in 20 seconds, acceleration took place in the first quarter-turn which occupied about 1.48 seconds; each successive quarter-turn occupied about 0.48 second, and retardation occupied approximately 0.74 second. The table stops smoothly and without noticeable jar to the animal. The cords are of silk permatite, a material used for stringing tennis racquets. This has to be replaced occasionally. Stretching of the cord which bears weight A has to be guarded against. In the illustration the structural dimensions may be roughly determined by comparison with the meter stick. The apparatus which has been described has proved satisfactory in a series of investigations covering nearly two years. It should be useful with any of the smaller laboratory animals where the period of rotation is limited. Sold by Wright and Ditson, San Francisco, California. MADISON BENTLEY, UNIVERSITY OF ILLINOIS HOWARD C. WARREN, PRINCETON UNIVERSITY (Review) SHEPHERD I. FRANZ, UNIV. OF CALIF., So. BR. (Monographs) S. W. FERNBERGER, UNIVERSITY OF PENNSYLVANIA (Bulletin) CONTENTS The Factor of Speed in Intelligence: HELEN PEAK AND EDWIN G. BORING 71 PERCY W. COBB 95 Further Observations on the Speed of Retinal Impression: The Ability of Chinese Students to Read in Vertical and Horizontal A Comparative Study of Stylus Maze Learning by Blind and Seeing The Visual Estimation of Angles: MARJORY BATES PRATT. ΙΙΟ 118 132 DAVID WECHSLER 141 A Spectrum Color-Mixer: C. E. FERREE AND GERTRUDE RAND...... 146 155 H. R. CROSLAND 162 PUBLISHED BI-MONTHLY BY PSYCHOLOGICAL REVIEW COMPANY PRINCE AND LEMON STREETS, LANCASTER, PA., AND Entered as second-class matter, July 1, 1920, at the post-office at Lancaster, Pa. EDITED BY HOWARD C. WARREN, PRINCETON UNIVERSITY (Review) JOHN B. WATSON, 244 MADISON Ave., NEW YORK (Review) SHEPHERD I. FRANZ, UNIV. OF CALIF., So. BR. (Monographs) MADISON BENTLEY, UNIVERSITY OF ILLINOIS (J. of Exp. Psych.) S. W. FERNBERGER, UNIVERsity of PennsyLVANIA (Bulletin) W. S. HUNTER, CLARK UNIVERSITY (Index) WITH THE CO-OPERATION OF MANY DISTINGUISHED PSYCHOLOGISTS PSYCHOLOGICAL REVIEW containing original contributions only, appears bimonthly, January, March, May, July, September, and November, the six numbers comprising a volume of about 480 pages. 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