^ 



THE '*£ 



LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



CONDUCTED BY 



SIR OUTER JOSEPH LODGE, D.So., 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 melior quia ex se fila gignunt, noc nostei* 

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



VOL. XXXVIII.— SIXTH SERIES. 

 JULY— DECEMBER 1919. 



S#6 2> 



LONDON-. 

 TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET. 



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

 AND VEUVE J. BOYVEAU, PARTS, 



