as applied to Gases and Vapours. '-'^^ jI/ 511 



a real nucleus having a nature distinct from that of the atmo- 

 sphere, or a portion of the atmosphere in a highly condensed 

 state, or merely a centre of condensation of the atmosphere, and 

 of resultant attractive and repulsive forces. Therefore, although 

 the word nucleus properly signifies a small central body, I shall 

 use it in this paper for want of a better term to signify an atomic 

 centre, whether a real nucleus or a centre of condensation and 

 force. I assume, however, that the volume of the nucleus, if any, 

 is inappreciably small as compared with that of the atmosphere. 



(4.) I have now to state a supposition, which, so far as I aift 

 aware, is peculiar to my own researches. It is this : — that the 

 vibration, which, according to the undulatory hypothesis, constitutes 

 radiant light and heat, is a motion of the atomic nuclei or centres, 

 and is propagated by means of their mutual attractions and repul- 

 sions. 



It will be perceived at once, that from the combination of this 

 supposition with the hypothesis of molecular vortices, it follows 

 that the absorption of light and of radiant heat consists in the 

 transference of motion from the nuclei to their atmospheres, and 

 conversely, that the emission of light and of radiant heat is the 

 transference of motion from the atmospheres to the nuclei. 



It appears to me that the supposition I have stated possesses 

 great advantages over the ordinary hypothesis of a luminiferous 

 aether pervading the spaces between ponderable particles, espe- 

 cially in the following respects. 



First. The propagation of transverse vibrations requires the 

 operation of forces, which, if not altogether attractive, are of a 

 very different nature from those capable of producing gaseous 

 elasticity, and which it is difficult to ascribe to such a substance an 

 the aether is supposed to be ; while attractive forces between the 

 atomic centres are perfectly consistent with their being kept 

 asunder by the elasticity of their atmospheres. 



Second. The immense velocity of light and radiant heat is a 

 natural consequence of this supposition, according to which the 

 vibrating masses must be extremely small as compared with the 

 forces exerted by them. 



Third. According to the most probable view of the theory of 

 dispersion, the unequal refrangibility of undulations of different 

 lengths is a consequence of the distances between the particles 

 of the vibrating medium having an appreciable magnitude as 

 compared with the lengths of the undulations. This is scarcely 

 conceivable of the sether, but easily conceivable of the atomic 

 nuclei. 



Fourth. The manner in which the propagation of hght and of 

 radiant heat is affected by the molecular arrangement of crystal- 

 line bodies is rendered much more intelligible if the vibrations 



2M2 



