PHYSICS: A. L. FOLEY 
Proc. N. a. S. 
Gold beaters skin in water is slightly electro-negative. Salts with univa- 
lent 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 AICI3 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 opera- 
tive 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 generaliza- 
tions 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 Bartell, F. E. and Hocker, C. D., /. Amer. Chem. Soc, 38, 1916 (1036). 
2 Robinson, C. S., /. Phys. Chem., 22, 1918 (99); 22, 1918 (153). 
^ Unpublished data. 
^ Girard, P., Rev. Gen. Set., 20, 1909 (694); Lillie, R. S., Amer. J. Physiol., 28, 1911 
(194). 
^Loeb, J., /. Gen. Physiol., 2, 1919 (87). 
A PHOTOGRAPHIC METHOD OF FINDING THE INSTANTANE- 
OUS VELOCITY OF SOUND WAVES AT POINTS NEAR THE 
SOURCE 
By Arthur L. Fol^y 
Department of Physics, Indiana University 
Communicated by R. A. Millikan, April 10, 1920 
Sparks fr(?m the condensers L, L (Leyden jars, charged by an electric 
influence machine not shown 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 (caused by refraction) of the sound wave produced 
by the spark at S upon the photographic dry plate P, provided the spark 
at I occurs at the proper time. The gaps I and S are in series, the spark 
at S occurring first, the spark at I being retarded the proper time interval 
by means of an adjustable condenser K. 
D is a steel disk 76 cm. in diameter mounted to rotate at high speed 
just in front of and near the lower edge of the dry plate P. The rim of 
the disk was ground to a chisel edge and very small teeth were cut in it at 
intervals of a cm. or so. The intervals and teeth were made irregular 
