4 06,7<3 
PROCEEDINGS ^ X 
OF THE 
National Academy 
of Sciences ^ 
OF THE 
UNITED STATES OF AMERICA 
VOLUME 7, 1921 
EXECUTIVE COMMITTEE 
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. 
