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I VOLUME 7 OCTOBER, 1921 NUMBER 10 
PROCEEDINGS 
OF THE 
National Academy 
of Sciences 
OF THE 
UNITED STATES OF AMERICA 
EXECUTIVE COMMITTEE 
Edwin Bid well Wilson, Managing Editor 
Raymond Pearl Vernon Kellogg 
P UBLISHED MONTHL Y 
Publication Office: Eschenbach Printing Company, Easton, Pa. 
Editorial Office: Massachusetts Institute of Technology, Cambridge 
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Home Office of the Academy: Washington, D. C. 
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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. 
