LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF 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. 

 GEORGE CAREY FOSTER, B.A., LL.D., F.R.S. 



AND 



WILLIAM FRANCIS, F.L.S. 



••Nee aranearum sane textus ideo meiior quia ex se tila gignunt, uec nostei" 

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



VOL. XXXVII.— SIXTH SERIES. 

 JANUARY— JUNE 1919. 



t ¥ZLo ^ 



LONDON: 

 TAYLOR AND FRANCIS, RED LION COURT. FLEET STREET. 



SOLD BY SIMPKIK, MARSHALL. HAMILTON, KENT. AND CO., ID 



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



AND VEUVE J. BOYVEAU, PAULS 



