THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



OCTOBER 1892. 



XXXV. On the Intensity of Light reflected from Water and 

 Mercury at nearly Perpendicular Incidence. By Lord 

 Rayleigh, Sec. R.S.* 



[Plate X.] 



IN a former paper f I gave an account of some experiments 

 upon the reflexion from glass surfaces tending to show 

 that " recently polished glass surfaces have a reflecting-power 

 differing not more than 1 or 2 per cent, from that given by 

 Fresnel's formula ; but that after some months or years the 

 reflexion may fall off from 10 to 30 per cent., and that with- 

 out any apparent tarnish." Results in the main confirmatory 

 have been published by Sir John ConroyJ. 



The accurate comparison of Fresnel's formula with observa- 

 tion is a matter of great interest from the point of view of 

 optical theory, but it seems scarcely possible to advance the 

 matter much further in the case of solids. Apart from con- 

 tamination with foreign bodies of a greasy nature, and disinte- 

 gration under atmospheric influences, we can never be sure that 

 the results are unaffected by the polishing-powder which it is 

 necessary to employ. For these reasons I have long thought 

 it desirable to institute experiments with liquids, of which 

 the surfaces are easily renewed ; and the more since I suc- 

 ceeded in proving that (in the case of water at any rate) the 

 deviation from Fresnel's formula found by Jamin in the 



* Communicated by the Author, 

 t Proc. Roy. Soc, November 1886. 

 % Phil. Trans. 1889 A, p. 245. 



Phil. Mag. S 5. Vol. 34. No. 209. Oct. 1892. Z 



