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VOLUME 6 
MAY, 1920 
NUMBER 5 
PROCEEDINGS 
OF THE 
National Academy 
OF Sciences 
OF THE 
UNITED STATES OF AMERICA 
EDITORIAL BOARD 
Raymond Pbarl, Chairman Edwin B. Wilson, Managing Editor 
C. G. Abbot, Home Secretary Georgk E. Haim, Foreign Secretary 
J. M. Clarke 
A. L. Day 
Gano Dunn 
E. B. Frost 
LUDVIG Hekto^n 
L. J. Henderson 
H. S. Jennings 
Jacques Loeb 
J. C. Merriam 
R. A. MlIvUKAN 
E. H. Moore ■ 
W. A. NoYES 
W. J. V. OSTERHOUT 
E. L. Thorndike 
w. M. Wheeler 
Publication Office : Eschenbach Printing Company, Easton, Pa. 
Editorial Office : Massachusetts Institute of Technology, Cambridge 
Home Office of the Academy^ Washington, D, C. 
Application pending for entry as second-class matter at the postofiBce at Easton, Pennsylvania, under the act of August 24, 1912. 
Acceptance for mailing 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 
