PHILOSOPHICAL 
TRANSACTIONS 
OF THE 
ROYAL SOCIETY 
OF LONDON. 
Series A. 
COKTAINING PAPERS OF A MATHEMATICAL OR PHYSICAL CHARACTER. 
VOL. 220. 
Printed and Published for the ROYAL SOCIETY by 
HARRISON AND SONS, 44-47, ST. MARTIN’S LANE, LONDON, W.C. 2, 
^rhittrs ill ®ri)inarg to ^is ^ajfstg. 
June, 1920. 
