J 



THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



CONDUCTED BY 



J31R 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. 

 RICHARD TAUNTON FRANCIS 



WILLIAM FRANCIS, F.L.S. 



"Nee aranearum sane textus ideo melior quia ex se fila gignunt, ncc noster 

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



VOL. XLL— SIXTH SERIES. 

 JANUARY— JUNE 1921. 



tlMk 



LOJV DON: 

 TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET 



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

 AND VEUVE J. BOVVBAU, PARIS, 



