CONTENTS Page GENETICS.-LINKAGE VARIATION AND CHROMOSOME MAPS. By A. H. Sturtevant 181 PALEONTOLOGY.-ORIGIN AND HISTORY of the Bear FAMILY IN THE WESTERN HEMISPHERE, WITH PARTICULAR REFERENCE TO THE RELATION OF THIS QUESTION TO PROBLEMS OF GEOGRAPHICAL HISTORY. By J. C. Merriam 183 BIOLOGY. AN UNIDENTIFIED BASE AMONG THE HYDROLYTIC PRODUCTS OF By D. D. Van Slyke and A. Hiller 185 GENETICS. Genetical and CYTOLOGICAL PROOF OF NON-DISJUNCTION OF THE FOURTH CHROMOSOME OF Drosophila Melanogaster GENETICS. THE BEHAVIOR OF HOMOLOGOUS CHROMOSOMES IN A TRIPLOID Canna PHYSICS. THE DESTRUCTION OF PHOSPHORESCENT ZINC SULFIDES BY ULTRA VIOLET LIGHT PHYSICS. ACOUSTIC PRESSURE DISTRIBUTIONS, CHIEFLY IN RESERVOIRS AND GENETICS. THE PREDICTION OF ANNUAL Egg ProduCTION FROM THE Records The HOME SECRETARY and the FOREIGN SECRETARY of the ACADEMY The CHAIRMAN and the PERMANENT SECRETARY of the NATIONAL Research COUNCIL WILLIAM DUANE, '23 A. L. DAY, '22 R. G. HARRISON, '23 GANO DUNN, '22 AUGUSTUS TROWBRIDGE CLARK WISSLER J. M. CLARKE, '21 F. L. RANSOME INFORMATION TO SUBSCRIBERS SUBSCRIPTIONS TO THE PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES at the rate of $5.00 per annum should be made payable to the National Academy of Sciences, and sent either to Easton, Pa., or to C. G. ABBOT, Home Secretary, National Academy of Sciences, Smithsonian Institution, Washington, D. C. Single numbers, $0.50. PAST publications of the NATIONAL ACADEMY OF SCIENCES are listed in these PROCEEDINGS, Volume III, pp. 743-753, December, 1917. In good part these publications are no longer available for distribution. Inquiries with regard to them should be addressed to the Home Secretary, National Academy of Sciences, Smithsonian Institution, Washington, D. C. PAST volumes of the PROCEEDINGS may be obtained at five dollars per volume unless the sale of the volume would break a complete set of Volumes I to V. Single numbers may be obtained for fifty cents except where the sale of such numbers would break up a complete volume. Only two hundred complete sets of the Proceedings are available for sale-Volumes I to VI, price $30.00. Orders should be sent to the Home Secretary, National Academy of Sciences, Smithsonian Institution, Washington, D. C. The following publications are issued by the NATIONAL RESEARCH COUNCIL. Orders and inquiries should be addressed: Publication Office, National Research Council, 1701 Massachusetts, Ave., Washington, D. C. (A) THE BULLETIN OF THE NATIONAL RESEARCH COUNCIL published at irregular intervals; Price $5.00 per volume of about 500 pages; individual numbers priced variously. (B) THE REPRINT AND CIRCULAR SERIES OF THE NATIONAL RESEARCH COUNCIL, individual numbers, variously priced. RYERSON PHYSICAL LABORATORY, UNIVERSITY OF CHICAGO Communicated by R. A. Millikan, June 3, 1921 By means of the audion oscillator, a special telephone receiver tuned to a high natural period and placed against the ear and a suitable circuit numerous tests at various frequencies have been made on the minimum audibility current for both normal and abnormal ears. From these data important conclusions can be drawn regarding the physical and physiological structure of the ear and also concerning the functioning of the ear and the auditory nerves with their endings as organs of hearing. The conclusions drawn, then, are based on precise physical measurements which can be checked to within about five per cent from time to time. Sensitivity of Normal Ears.—Ears are considered normal when no physiological defects are observable by the otologist. If we define sensitivity as the reciprocal of the minimum vibrational energy in ergs of the receiver diaphragm that the normal ear can detect, then curves can be plotted showing the sensitivity as a function of the frequency. This has been done for a number of normal ears. The curve shown in figure 1 is a typical one. It is to be observed that up to about 6000 cycles three distinct maxima of sensitivity are present; one at 900 cycles, one 1800 and another one at 3900. It is also important to observe that the sensitivity is much greater throughout the region from 200 to 4500 cycles than outside this range. Within this region are included all the frequencies which are of most importance for both speech and music. The natural period of the receiver was 5215 cycles when this curve was taken and the absence of a peak in this position shows that the receiver characteristics have been corrected for satisfactorily. All the maxima, then, occur below the resonant frequency of the receiver. Curves on other normal ears show maxima which agree for the most part in location but not in magnitude with the curve shown in figure 1. Because of the marked similarity between the response curves for coupled mechanical vibratory systems and the curves for normal ears, it seems |