230 Prof. J. H. Jeans on Temperature-Radiation 



walls reflect energy perfectly. These conditions cannot be 

 realized experimentally; so that it is not known what would 

 happen. But it is commonly supposed that the temperatures 

 of the bodies would equalize * by radiation, so that after an 

 •infinite time the bodies would all be at the same tempe- 

 rature T ; also the aether, the vehicle of energy from one body 

 to another, would be possessed of a certain amount of energy, 

 and in spite of the continual transference and retransference 

 of energy between matter and aether, the amount of energy 

 •in the aether, and the law of its distribution between different 

 wave-lengths, would remain constant. In this supposed state, 

 let the energy per unit volume of radiation of wave-lengths 

 intermediate between \ and \ + d\ be assumed to be 



F(\, T)d\ (1) 



3. The position of the masses of matter inside the enclosure 

 lias been immaterial. Let them now be supposed spread over 

 the walls, so that every part of the original perfectly-reflecting 

 walls is covered. So far the whole system inside the re- 

 flecting walls has remained impervious to energy. Let a 

 minute hole now be made at any point in one of the walls, 

 and let the radiant energy stream through this hole into 

 external space (which may, for simplicity, be thought of as 

 devoid of radiant energy). At first the issuing stream of 

 radiant energy will be of constitution given by formula (1) ; 

 but in time, as the total amount of energy inside the enclosure 

 diminishes, the constitution of the escaping energy will 

 change. The flow of energy could be kept constant, provided 

 energy of the appropriate amount and constitution could 

 be supplied to the inside of the enclosure. There would 

 then be a steady flow of energy through the aperture, of 

 constitution given by formula (1). 



4. Suppose that the walls are no longer perfectly-reflecting, 

 but are provided with a mechanism which keeps them at a 

 uniform temperature T. The flow of energy through the 

 small aperture must now be "steady": experiment shows it 

 to be independent of the nature and reflecting power of the 



* This is the orthodox view. Equalization is commonly supposed 

 to be a necessity, from the second law of thermodynamics. My own view 

 is that equalization loould take place, but only because the charges 

 on the electric sources of radiation would be identical in the different 

 masses of matter. If the electrons in one mass were more heavily- 

 charged than those in the other masses, I believe the temperatures 

 would tend to become different, in opposition to the second law. 

 (Cf. Phil. Mag. [6]xii. p. 57.) 



