Interaction between Radiation and Electrons. 1067 



it seems clear that in general the shorter the wave-length of 

 the radiation, the greater the possibility of its being so 

 absorbed, because the length of free path necessary to fulfil 

 the condition would be correspondingly small and would the 

 more frequently occur. There would therefore be selective 

 absorption of small wave-length vibrations, and the tendency 

 for the energy all to be absorbed into smaller and smaller 

 vibrations would be prevented. 



The electron which constitutes part of the system of an 

 atom also may be able to absorb similarly, since, within limits, 

 it may be free to move in the direction perpendicular to the 

 plane of its orbit. In that way it also may be a selective 

 absorber of the smaller wave-lengths of radiation. 



The writer is disposed to go further, however, in criticism 

 of the argument that energy must, on Xewtonian principles, 

 fritter away into the minutest chaotic motions. It is 

 submitted that the possibilities of thermo-dynamic analogy 

 have not. been exhausted, and that even if we forget ihe 

 Faraday lines and treat the electron in the aether as analogous 

 to a heavy particle in a kind of gas composed of far more 

 minute particles than any ordinary material gas. the argument 

 that the heavy particle must lose all its energy does not 

 necessarily hold good when we proceed from the finite case 

 to the infinite, or when we at least entirely alter the order 

 of magnitude of our gas molecules. 



Jeans* takes the formula for distribution of energy between 

 X molecules of air at temperature T and n heavy spheres. 

 "The total energy in the steady state will be (|N + f»)HT, 

 and T will be determined from the condition that this 

 quantity must be equal to the total energy of the original 

 oscillations of the spheres. Since N, the number of mole- 

 cules, will be enormously large compared with n, the number 

 of spheres, it is clear that practically all the energy will be 

 contributed by the term ^^R™- By the time the steady 

 state is reached the energy is almost entirely transferred from 

 the spheres to the gas." 



The principle is the same if the energy is dealt with in 

 terms of sound-waves. 



The question is, however, whether, if we are going to make 

 X enormously greater than it would be in the case of any 

 actual gas, there are not some considerations to be taken into 

 account which can be neglected as unimportant so long as 

 we are dealing with familiar gases. 



Starting from the conception of a familiar gas, such as air 

 or hydrogen, having N molecules in a given space, we must 



* Report, p. 5. 



