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VOLUME 6 SEPTEMBER, 1920 NUMBER 9 
= « 
PROCEEDINGS 
OF THE 
National Academy 
OF Sciences 
OF THE 
UNITED STATEvS OF AMERICA 
EDITORIAL BOARD 
Raymond Pkari^, Chairman Edwin B. Wilson, Managing Editor 
C. G. Abbot, Home Secretary Georgk E. Hale, Foreign Secretary 
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 
E. H. Moore 
W. A. NoYES 
W. J. V. OSTERHOUT 
E. ly. Thorndike 
W. M. Wheeler 
PUBLISHED MONTHLY 
1 Publication Office : Eschenbach Printing Company, Easton, Pa. g 
M Editorial Office : Massachusetts Institute of Technology, Cambridge | 
m Home Office of the Academy: Washington, D. C. E 
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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 
