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VOLUME 6 
MARCH, 1920 
NUMBER 3 
I 
PROCEEDINGS 
OF THE 
National Academy 
OF Sciences 
OF THE 
UNITED STATES OF AMERICA 
EDITORIAL BOARD 
Raymond Pkarl, Chairman Edwin B. Wilson, Managing Editor 
G. G. Abbot, Home Secretary George E. Hale, Foreign Secretary 
J. M. Clarke 
A. L. Day 
Oano 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. L. Thorndike 
W. M. Wheeler 
Publication Office: Eschenbach Printing pompany, Easton, Pa. 
Editorial Office: Massachusetts Institute of Technology, Cambridge 
Home Office of the Academy: Washington, D. C. 
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Application pending for entry as sec<MJd-class matter at the postoflSce at Easton, Pennsylvania, under the act of August 24, 1912. 
Acceptance for maiUng at special rate of postage provided for in Section 1 103, Act of October 3, 1917. Authorized on July 3, 1918. 
Price per annum, $5.00 
