284. Mr KELLAND, ON THE MOTION OF 



The above, however, is sufficiently accurate for my present pur- 

 pose, which is merely to give a colour to my investigations, and to 

 shew that, at least, they tend towards the trutli. 



53. I do not suppose the same results would be applicable to 

 solids, even if they are to fluids. For in solids the effect is modified 

 or altogether destroyed by the action of the material particles. Indeed, 

 the quantity of either kind of particles, and the arrangement of them 

 within the body must depend so much on the constitution of the body, 

 that, in many cases, I could imagine no ether, and, in others, no 

 caloric, according as either from the disposition of the material par- 

 ticles or their peculiar nature, the forces which the one or the other 

 exerts would keep up an equilibrium with the external forces of the 

 mixed ether and caloric. 



And even fluids from their greater or less fluidity would in like 

 manner essentially modify the effects of transmission of vibrations 

 throucrh them: instances of the above we have seen in the case of 

 lio-ht, to which I have before alluded. At the same time that I make 

 these remarks, I have not attempted either to- verify or disprove the 

 above analogy. 



54. The connexion which we thus establish between light and heat 

 is of the most intimate description. I shall briefly mention one or two 

 circumstances in the latter, which can be readily explained. 



Reflexion of light must arise from the vibrations at the reflecting 

 surface being stopped: it is evident then that the transmission, put 

 in play by such vibrations, will also be stopped; hence if heat be in 

 the act of emerging from a polished metal, when the pulsations reach 

 the surface they will diminish greatly in magnitude, and thus the 

 corresponding impulse of radiation Avill be small, whilst from an un- 

 polished surface, the converse will be the case. The same is true of 

 the acquisition of heat. This is abundantly confirmed by experiment. 

 The same reasoning applies to total internal reflexion for heat as for 

 light, with the exception that in the former the word total would refer 

 only to such motion as is due to the action of the vibratory forces. 



