THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



nl 



3) , 



[SIXTH SERIES.] 



SEPTEMBER 19( 



; 



XXXII. On the Weights of Atoms. 



Bi, Lord Kelvin, G. C. V. 0. ^^X 



By 



[Concluded from page 198.] 



'§ 52. A NEW method of finding an inferior limit to the 

 Jl\. number of molecules in a cubic centimetre of 

 a gas, very different from anything previously thought of, 

 and especially interesting to us in connexion with the wave- 

 theory of light, was given by Lord Rayleigh *, in 1899, as a 

 deduction from the dynamical theory of the blue sky which 

 he had given 18 years earlier. Many previous writers, 

 Newton included, had attributed the light from the sky, 

 whether clear blue, or hazy, or cloudy, or rainy, to fine 

 suspended particles which divert portions of the sunlight from 

 its regular course ; but no one before Rayleigh, so far as I 

 know, had published any idea of how to explain the blueness 

 of the cloudless sky. Stokes, in his celebrated paper on 

 Fluorescence f, had given the true theory of what was known 

 regarding the polarization of the blue sky in the following 

 " significant remark " as Rayleigh calls it : "Now this result 

 " appears to me to have no remote bearing on the question of 

 " the directions of the vibrations in polarized light. So long 

 "as the suspended particles are large compared with the waves 

 u of light, reflexion takes place as it would from a portion of 

 • ; the surface of a large solid immersed in the fluid, and no 

 "conclusion can be drawn either way. But if the diameter 



* Rayleigh, Collected Papers, vol. i. art. viii. p. 87. 

 f " On the Change of Refrangibility of Light," Phil. Trans. 1852, and 

 Collected Papers, vol. iii. 



Phil Mag. S. 6. Vol. 4. No. 21. Sept. 1902. U 



