THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



CONDUCTED BY 



SIR DAVID BREWSTER, K.H. LL.D. F.R.S.L. & E. &c. 

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

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

 JOHN TYNDALL, F.R.S. &c. 



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

 vilior quia ex alienis libamus ut apes." Just. Lips. Polil. lib. i. cap. 1. Not. 



VOL. XX.— FOURTH SERIES. 

 JULY— DECEMBER, 1860. 



LONDON. 



TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET, 

 Printers and Publishers to the University of London ; 



SOLD BY LONGMAN, GREEN, LONGMANS, AND ROBERTS ; SIMPKIN, MARSHALL 



AND CO.; WHITTAKER AND CO.; AND PIPER AND CO., LONDON: 



BY ADAM AND CHARLES BLACK, AND THOMAS CLARK, 



EDINBURGH* SMITH AND SON, GLASGOW ; HODGES 



AND SMITH, DUBLIN ; AND PUTNAM, 



NEW YORK. 



