1 
I 
VOLUME 6 
JUNE, 1920 
PROCEEDINGS 
OF THE 
NUMBER 6 
National Academy 
OF Sciences 
OF THE 
UNITED STATES OF AMERICA 
I 
EDITORIAL BOARD 
Raymond Peari., Chairman Edwin B. Wii^son, Managing Editor 
C. G. Abbot, Home Secretary George E. Hale, Foreign Secretary 
I 
J. M. Clarke 
A. L. Day 
Gano Dunn 
E. B. Frost 
LUDVIG Hektoen 
L. J. Henderson 
H. S. Jennings 
Jacques Loeb 
J. C. Merriam 
R. A. MiLLIKAN 
PUBLISHED MONTHLY 
E. H. Moore 
W. A. NOYES 
W. J. V. OSTERHOUT 
E. L. Thorndike 
w. M. Wheeler 
Publication Office: Eschenbach Printing Company, Easton, Pa. 1 
Editorial Office: Massachusetts Institute of Technology, Cambridge 1 
Home Office of the Academy: Washington, D. C. 1 
illllllllllllllllllllllllliillllilllllllll^^ 
Entered as second class matter June 21, 1920, at the postoffice at Easton, Fennsylvania, under the act of Au^^i st 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 
