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



Let us, for the present, continue to denote R and h by 

 separate symbols, leaving open the question of whether or 

 not the quantities they represent are identical. If these 

 quantities are not identical, then the formulae (3) and (4) are 

 entirely different. But if they are found to be identical, then 

 the formulae will be seen to coincide for light of great wave- 

 length, but to diverge widely for light of visible or very short 

 wave-length. 



6. The divergence between the two formulae, whether 

 complete or partial, raises various questions, to which the 

 analysis of the present paper attempts to provide answers. 

 It is natural to inquire — 



(1) Is the uce of the Theorem of Equipartition, and con- 

 sequent derivation of formula (3), legitimate? 



(2) If so, what is the essential difference between the 

 physical conditions which lead to formula (3) and those 

 which lead to formula (4) ? 



(3) If equation (1) is answered in the affirmative, do 

 formulae (3) and (4) become identical for long wave-lengths : 

 and if so, why ? 



It may simplify what follows to state briefly in advance 

 the conclusions arrived at. 



7. It is found that question (1) can be definitely answered 

 in the affirmative, but that the theorem of equipartition 

 represents merely the tendency for energy to become de- 

 graded into irregular disturbances of the medium, and the 

 utility of the theorem of equipartition (although not, of 

 course, its truth) is limited by the circumstance that it 

 represents a state attained only after enormous, or infinite, 

 time. 



The answer obtained to question (2) can be best explained 

 by making use of an acoustical analogy. Let the aether be 

 replaced by air : let waves of light in the aether be repre- 

 sented by waves of sound in air. Matter may be represented 

 by a series of musical or noise-producing instruments : these 

 will of course be capable of absorbing as well as emitting 

 sound. 



To represent the state of things considered in § 4, we 

 have to imagine the walls of a room to be covered conti- 

 nuously with sound-instruments (to make the picture clearer, 

 let us say telephone diaphragms), and we suppose that these are 

 kept in vibration by agencies acting from outside the room. 

 A person listening at an aperture in the wall of the room will 

 hear the sound of the telephones (modified by the reflexion 

 and absorption of the other diaphragms, perhaps): the 



