Vol. 36. JULY 1868. No. 240. 



Published the First Day of every Month. — Price 'is. 6d. 



THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE, 



AND 



JOURNAL OF SCIENCE. 



Being a Continuation of Tilloch's 'Philosophical Magazine,' 

 Nicholson' 8 'Journal,' and Thomson's 'Annals of Philosophy ' 



CONDUCTED BY 



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



AND 



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



FOURTH SERIES. 



N° 240.— JULY 1868. 



LONDON: 



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



Printers and Publishers to the University of London. 



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

 Co. ; Whittaker and Co. ; andH. Bailliere, London -.—and by A. and C. Black, and 

 Thomas Clark, Edinburgh; Smith and Son, Gflasgow : — Hodges and Smith, 

 Dublin : — and Putnam, New York. 



Agrnry of Smithsonian Institution. 

 WILLIAM WESLEY, 



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