Mechanics of Luminosity. 391 



(1) We may assume that it is the material particles them- 

 selves which vibrate and thus cause the emission of light ; 

 in this case Gr=l. 



(2) We may assume that it is the luminiferous aether sur- 

 rounding the molecule which vibrates. The weight of the 

 vibrating luminiferous aether may be found as follows : — The 

 weight of a molecule of hydrogen* is, according to the kinetic 

 theory of gases, 15 x 10" 23 gr., its volume 4 x 10 ~ 25 cub. cent. 

 Now the density of luminiferous aether in reference to water 

 is 10~ 17 ; the weight of the aether contained in the volume of 

 a hydrogen molecule is therefore of the order of magnitude 



4x 10- 25 10~ 17 = 4x lO" 42 gramme ; 



its weight is therefore 4 x 10" 4 7(15 X 10" 23 ) = 2*6 x 10~ 20 that 

 of the hydrogen molecule. Therefore in this case 



G = 2-6xl0- 20 gr. 



In this we make the simplest assumption for the calculation, 

 that the luminiferous aether occupies the whole volume of the 

 material molecule, and further that it possesses the same den- 

 sity in the bodies as in vacuo. If we should allow the density 

 of the aether to change in accordance with the indices of 

 refraction, or form only an envelope surrounding the molecule, 

 the order of magnitude of the values obtained would not be 

 altered. 



(1) Vibrating material particles, 



a2 K = 4^Tos§ (metre)2 - 



(2) Vibrating aether particles, 



1 ~p] 11? 



< = MVW 6 M x 2-6 x io-( metre )*= i^O0« Jb (metre)5 



We will now determine the magnitudes a K and a A for 

 sodium and platinum. 

 For sodium, 



E =3-2 x 10 3 gr. cal., Z>=10 8 , a = 5 ; 



whence it follows, if we now put millimetres instead of metres, 



a K =l-7xl0- 13 millim. 



a A = l-lxl0- 3 „ 



For platinum, we obtain, if we put for b the value which it 



* Upon the dimensions, weights, &c. of the molecules see R. Riihl- 

 mann, Mechanische Warmtheorie, ii. p. 245 (1885). 



