Dynamical Theory of Heat and Light. 3 



grasped this idea, they must have noticed the enormous 

 difficulty presented by the laceration which the ether must 

 experience if it moves through pores or interstices among 

 the atoms of matter. 



§ 3. It has occurred to me that, without contravening 

 anything we know from observation of nature, we may 

 simply deny the scholastic axiom that two portions of matter 

 cannot jointly occupy the same space, and may assert, as an 

 admissible hypothesis, that ether does occupy the same space 

 as ponderable matter, and that ether is not displaced by 

 ponderable bodies moving through space occupied by ether. 

 But how then could matter act on ether, and ether act on 

 matter, to produce the known phenomena of light (or radiant 

 heat), generated by the action of ponderable bodies on ether, 

 and acting on ponderable bodies to produce its visual, 

 chemical, phosphorescent, thermal, and photographic effects ? 

 There is no difficulty in answering this question if, as it 

 probably is, ether is a compressible and dilatable * solid. 

 We have only to suppose that the atom exerts force on the 

 ether, by which condensation or rarefaction is produced 

 within the space occupied by the atom. At present f I 

 confine myself, for the sake of simplicity, to the suggestion 

 of a spherical atom producing condensation and rarefaction, 

 with concentric spherical surfaces of equal density, but the 

 same total quantity of ether within its boundary as the 

 quantity in an equai volume of free undisturbed ether. 



§ 4. Consider now such an atom given at rest anywhere in 

 space occupied by ether. Let force be applied to it to cause 

 it to move in any direction, first with gradually increasing 

 speed, and after that with uniform speed. If this speed is 

 anything less than the velocity of light, the force may be 

 mathematically proved to become zero at some short time 

 after the instant when the velocity of the atom becomes 

 uniform, and to remain zero for ever thereafter. What takes 

 place is this : 



§ 5. During all the time in which the velocity of the atom 

 is being augmented from zero, two sets of non-periodic waves, 

 one of them equi-voluminal, the other irrotational (which is 

 therefore condensational-raref actional), are being sent out in 



* To deny this property is to attribute to ether infinitely great resist- 

 ance against forces tending to condense it or to dilate it — which seems, 

 in truth, au infinitely difficult assumption. 



t Further developments of the suggested idea have been contributed 

 to the Royal Society of Edinburgh, and to the Congres International de 

 Physique, held in Paris in August. (Proc. R.8.E. July 1900 ; vol. of 

 reports, in French, of the Cong. Inter. ; and Phil. Mag., Aug., Sept., 

 1900.) 



B2 



