The Specific Heat of Carbon Dioxide and Steam. 551 



It was not of course to be anticipated that our work should 

 give any effect perceptible experimentally for the distribu- 

 tion of lines in the hydrogen spectrum, but it is interesting 

 to observe what extremely little difference the finite mass of 

 the hydrogen nucleus does make. In the first place there 

 is the factor M/(M + w) in the large terms, corresponding 

 to a slight alteration in Balmer's constant. This comes out 

 of ordinary dynamics and was given by Sommerleld. Jn 

 addition, we have a minute shift of the whole position of 



, -it , i i ±\ -1 Mm 



the composite lines, represented by the term m - / -^- T -x. 



1 4 (M -I- my 



But the fine structure of each line, which is given by the 

 term in nfjn, remains absolutely unaffected by the mass of 

 the nucleus. 



LII. The Specific Heat of Carbon Dioxide and Steam. 

 By W. T. David, M.A* 



1. TE^HE specific heat of many gases, notably carbon dioxide 

 JL and steam, increases very considerably with tem- 

 perature. In this paper the suggestion is put forward that 

 the specific heat of these gases depends to an appreciable 

 extent upon volume and density as well aS temperature. 



2. Some of my experiments upon the emission of radiation 

 in gaseous explosions indicate that the intrinsic radiance from 

 thicknesses of gas containing the same number and kind of 

 radiating molecules does not depend upon the temperature 

 alone, even after correcting the radiation for absorption. 

 This implies that the vibratory energy of the radiating mole- 

 cules is not solely dependent upon the gas temperature. It 

 depends upon the volume and the density of the gas as well*]". 

 I have suggested! an explanation of this in terms of the 

 kinetic theory of gases which it will be convenient to repeat 

 here briefly. A radiating molecule as it describes its Iree- 

 path loses energy owing to the emission of radiation and 

 gains energy owing to the absorption of energy from the 

 aether. Its vibratory energy will thus increase or decrease 

 according as the absorption is greater or less than the emis- 

 sion. During collision with another molecule there will be 

 a transference of energy between the vibratory and the 

 rotational and translational energies, which, as Mr. Jeans 



* Communicated by the Author. 



t Phil. Trans. A. vol. ccxi. (1911) pp. 402 & 406. 



t.Phil. Mag-. Feb. 1913, p. 267. 



