158 



ON THE IDENTITY OF LIGHT, HEAT, 



force under investigation — 1 refer to the experimental labours 

 of M. Melloni and Professor Draper. 



We have, therefore, deficient only one link in the chain 

 of identity among all these imponderable forces, and that 

 link is the identity of the force light or heat, with electricity. 

 I have already shewn that there are many points of analogy 

 between voltaic electricity and the calorific force. Each of 

 these forces is found occupying the interior or so-called 

 interstitial space of the elements of bodies, they are the 

 admitted agents which operate upon the elementary particles 

 or atoms of matter,* and are possessed of essential qualities 

 common to both, which are exhibited in all their lumini- 

 ferous and calorific phenomena. 



It is this link which I believe is discovered and supplied 

 by the following experiments. The account of these is 

 copied almost verbatim from my experimental note book, 

 from November, 1850. 



My delicate galvanometer, which has been employed in all 

 my previous experiments, is composed of a helix of forty-six 

 turns of covered copper wire ^ of an inch in diameter, and 

 a single needle suspended by about 16 or 18 inches of silk 

 fibre — the indicator is a slender wooden fibre, and moves over 

 a card dial, which shades the upper surface of the helix. 



I found on placing it in a window having a southern aspect, 

 that it was impossible in the day time to obtain at all times 

 certain indications. At other times I observed a constant 

 vibratory motion to such an extent that I was unable to pro- 

 ceed with my experiments. Desiring to discover the reason 

 of such action, on the 14th of November last, the needle 

 at that time vibrating to a considerable extent, I intercepted 

 the progress of the suns rays, which were shining upon 

 the southern extremity of the galvanometer, by a book or any 

 thing near at hand, and the needle became stationary. On 



* This is not the case with any of the other forces. See Keport of British 

 Association for 1842. 



