T H E 

 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. 

 RICHARD TAYLOR, F.L.S.G.S. Astr.S.Nat.H.Mosc.&c. 

 RICHARD PHILLIPS, F.R.S. L.&E.F.G.S. &c. 



AND 



ROBERT KANE, M.D. M.R.I.A. 



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

 vilior quia ex alienis libamus ut apes." JUST. LIPS. Monit. Polit. lib. i. cap. 1. 



VOL. XVII. 



NEW AND UNITED SERIES OF THE PHILOSOPHICAL MAGAZINE, 

 ANNALS OF PHILOSOPHY, AND JOURNAL OF SCIENCE. 



JULY DECEMBER, 1840. 



LONDON: 



RICHARD AND JOHN E. TAYLOR, RED LION COURT, FLEET STREET, 

 Printers and Publishers to the University of London; 



SOLD BY LONGMAN, ORME, BROWN, GREEN, AND LONGMANS; CADELL; 



SIMPKIN AND MARSHALL; s. HIGHLEY ; WHITTAKER AND co.; AND 



SHERWOOD, GILBERT, AND PIPER, LONDON : BY ADAM AND 



CHARLES BLACK, AND THOMAS CLARK, EDINBURGH ; SMITH 



AND SON, GLASGOW ; HODGES AND SMITH, DUBLIN : 



AND G. W. M. REYNOLDS, PARIS. 



