PHILOSOPHICAL 
TRANSACTIONS 
OF THE 
ROYAL SOCIETY OF LONDON. 
Series A. 
CONTAINING PAPERS OF A MATHEMATICAL OR PHYSICAL CHARACTER. 
VOL. 217. 
LONDON: 
PRINTED BY HARRISON AND SONS, ST. MARTIN^ LARIE, W.C., 
V 
printers in (Srbinarg to fiis Hlajfstjj. 
December, 1918. 
