42. SEPTEMBER 1871. No. 279 



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



THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE, 



AND 



JOURNAL OF SCIENCE. 



Being a Continuation of Tilloch's l Philosophical Magazine? 

 Nicholson's ' Journal/ and Thomson's ' Annals of Philosophy S 



CONDUCTED BY 



SIR ROBERT KANE, LL.D. F.R.S. M.R.I.A. F.C.S. 

 SIR WILLIAM THOMSON, Knt. LL.D. F.R.S. &c. 



AND 



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



FOURTH SERIES. 



N° 279.— SEPTEMBER 1871. 



LONDON: 



PBINTED BY TAYLOB AND FBANCIS, BED LION COUBT, FLEET STBEET, 

 Printers and Publishers to the University of London. 

 Sold by Longmans, Green, Reader and Dyer j Kent and Co. ; Simpkin, Marshall and 

 Co. j Whittaker and Co. j andH. Bailliere, London :— and by A. and C. Black, and 

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 Dublin ; — Putnam, New York : — and Asher and Co., Berlin. 



