THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



CONDUCTED BY 



SLR 0LI7ER 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, noo noster 

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



VOL. XLIL— SIXTH SERIES. 

 JULY— DECEMBER 1921. 



?2-C7 



LONDON-. 

 TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET. 



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

 AND VEUVE J. BOYVKAU, PARIS, 



