PROCEEDINGS 
OF THE 
National Academy 
OF Sciences 
OF THE 
UNITED STATES OF AMERICA 
VOLUME 6, 1920 
EDITORIAI. BOARD 
Raymond Pkarl, Chairman Edwin B. Wilson, Managing Editor 
C. G. Abbot, Home Secretary GeJorgk E- HalK, Foreign Secretary 
J. M. Clarke: L. J. Henderson E. H. Moore 
- — - A. ly. Day H. S. Jennings W. A. Noyes 
Gano Dunn Jacques Loeb W. J. V. Osterhout 
E- B. Frost J. C. Merriam E. L. Thorndike 
LuDviG Hektoen R. a. Milukan 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. 
