Vol. 31. FEBRUARY 1891. No. 189. 



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



THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE, 



AJSTD 



JOURNAL OF SCIENCE. 



Being a Continuation of Tilloc'tis 'Philosophical Magazine? 

 Nicholson s 'Journal? and Thomson's 'Annals of Philosophy.' 



CONDUCTED BY 



SIR WILLIAM THOMSON, Knt. LL.D. P.E.S. &c. 

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



AND 



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



FIFTH SERIES. 



N° 189.— FEBRUARY 1891. 



WITH ONE PLATE. 



Illustrative of Lord Rayleigh's Paper on Pin-hole Photography. 



LONDON: 



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



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

 and by A. and C. Black, and T. and T. dark, Edinburgh; Smith and Son, 

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