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VOLUME 7 MAY. 1921 _ NUMBER 5 
PROCEEDINGS 
OF THE 
| National Academy 
of Sciences 
OF THE 
UNITED STATES OF AMERICA 
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1 ' EXECUTIVE COMMITTEE 
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| Edwin Bidweix Wilson, Managing Editor 
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I Raymond Prari, Vernon Keu,ogg 
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1 P UBLISHED MONTHL Y 
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| Publication Office: Eschenbach Printing Company > Easton, Pa. 
Editorial Office: Massachusetts Institute of Technology, Cambridge 
J 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, 1012. 
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 
