illllllllllillllllllllilllllllllllliUlillllllllllllllllllllH^ 
VOLUME 6 
JULY, 1920 
PROCEEDINGS 
OF THE 
NUMBER 7 
National Academy 
OF Sciences 
OF THE 
UNITED STATES OF AMERICA 
EDITORIAL BOARD 
Raymond Peari., Chairman Edwin B. Wilson, Managing Editor 
C. G. Abbot, Home Secretary George E. Hai.e, Foreign Secretary 
J, M. Clarke 
A. L. Day 
Gano Dunn 
E. B. Frost 
LUDVIG Hektoen 
E. H. Moore 
W. A. NOYES 
W. J. V. OSTERHOUT 
E. L. Thorndike 
w. M. Wheeler 
L. J. Henderson 
H. S. Jennings 
Jacques Loeb 
J. C. Merriam 
R. A. MilIvIkan 
— ^= 
1 , 1 
m m 
i PUBLISHED MONTHLY 1 
M ' = 
1 Publication Office : Eschenbach Printing Company, Easton, Pa. 1 
1 Editorial Office: Massachusetts Institute of Technology, Cambridge 1 
M Home Office of the Academy: Washington, D. C. | 
I I 
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii 
Entered as second class matter June 21, 1920, at the postoffice at Easton, Pennsylvania, under the act of August 24, 1912. 
Acceptance for mailing at special rate of postage provided for in Section 1103, Act of October 3, 1917. Authorized June 18, 1920. 
Price per annum, $5 00 
