Vol. 35. APRIL 1893. No. 215. 



Published the First Bay of every Month. — Price '2s. 6d. 



THE -^ L n 



LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE, 



AND 



JOURNAL OF SCIENCE. 



Being a Continuation of Tilloclis i 'Philosophical Magazine? 

 Nicholsons i Journal , and Thomson's 'Annals of Philosophy J* 



CONDUCTED BY 



LORD KELVIN, LL.D. P.R.S. &c. 



GEORGE FRANCIS FITZGERALD, M.A. Sc.D. F.R.S, 



AND 



WILLIAM FRANCIS, Ph.D. F.L.S. F.R.A.S. F.C.S. 



FIFTH SERIES. 



N° 215.— APRIL 1893. 



LONDON: 



PRINTED BY TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET. 



Sold by Simpkin, Marshall, Hamilton, Kent, and Co., Ld.; Whittaker and Co. ; 

 and by A. and 0. Black ;— T. and T. Clark, Edinburgh ; Smith and Son, 

 Glasgow: — Hodges, Figgis, and Co., Dublin: — Putnam, New York: — Veuve J. 

 Boyveau, Paris: — and Ashor and Co., Berlin. 



