THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OK SCIENCE. 



CONDUCTED BY 



SIR OLIVER JOSEPH LODGE, D.Sc, LL.D., F.R.S. 



SIR JOSEPH JOHN THOMSON, O.M., M.A., Sc.D., LL.D., F.R.S, 



JOHN JOLY, M.A., D.Sc, F.R.S,, F.G.S. 



AND 



WILLIAM FRANCIS, F.L.S. 



"Nee aranearum sane textus ideo raelior quia ex se fila gignunt, noc noster 

 vilior quia ex alienis libamus ut apes." Just. Lips. Polit. lib. i. cap. 1. Not. 



VOL. XXXIX.— SIXTH SERIES. 

 JANUARY— JUNE 1920. 



I^_fc 



LONDON-. 

 TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET. 



SOLD BY SMITH AND SON, GLASGOW: — HODGES, FIGGIS, AND CO. DUBLIN; — 

 J&D YEUVE J. BOYVEAU, PARIS. 



