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PHYSICS: A. L. FOLEY 310 PROC. N. A. S. Gold beaters skin in water is slightly electro-negative. Salts with univalent cations may cause the membrane material to become positively charged. The magnitude of the charge on the capillary walls increases with increase in valency of the cation. This explains the abnormally great osmose with AlCl3 solution. It is noted that the direction and the extent of osmose in the above experiments conform to predictions which follow from the application of the postulates given above. In those cases in which the direction of flow is not that actually indicated by the sign of the charge of the system, it will be noted that the osmose is abnormal and that the tendency is operative in the direction predicted. The experiments with various types of membranes have been extended considerably beyond those cited. Parchment paper, gold beaters skin, collodion, and gelatine membranes have been studied. The generalizations outlined above have been found to apply very satisfactorily in the case of each of these types of membranes. The results will be published in the near future. 1 2 Bartell, F. E. and Hocker, C. D., J. Amer. Chem. Soc., 38, 1916 (1036). Robinson, C. S., J. Phys. Chem., 22, 1918 (99); 22, 1918 (153); 3Unpublished data. 4Girard, P., Rev. Gen. Sci., 20, 1909 (694); Lillie, R. S., Amer. J. Physiol., 28, 1911 (194). Loeb, J., J. Gen. Physiol., 2, 1919 (87). A PHOTOGRAPHIC METHOD OF FINDING THE INSTANTANEOUS VELOCITY OF SOUND WAVES AT POINTS NEAR THE SOURCE By ARTHUR L. FOL13Y DEPARTMENT OF PH5YSICS, INDIANA UNIVERSITY Communicated by R. A. Millikan, April 10, 1920 Sparks frem the condensers L, L (Leyden jars, charged by an electric influence machine not showti in the figure) pass across the gaps G, G, the sound gap S, and the illuminating gap I. The light from the spark at I casts a shadow (cause