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I VOLUME 7 APRIL, 1921 
NUMBER 4 
PROCEEDINGS 
OF THE 
National Academy 
of Sciences 
OF THE 
UNITED STATES OF AMERICA 
1 
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EXECUTIVE COMMITTEE 
H 
Edwin Bid well Wilson, Managing Editor 
Raymond Pearl Vernon Kellogg 
PUBLISHED MONTHLY 
Publication Office : Eschenbach Printing Company, Easton, Pa. 
Editorial Office: Massachusetts Institute of Technology, Cambridge 
| 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. 
Price per annum, $5.00 
