278 Mr. Potter's "Reply to Professors Airy and Hamilton. 



quiries. Amongst the objections not generally raised, which 

 occur to me at the moment, I may mention, that the heating 

 properties of one end of the solar spectrum and the chemical 

 effects produced at the other, seem very inadequately ac- 

 counted for to a chemist, by a small difference in the lengths 

 of the undulations. The whole connexion of light, heat, and 

 electricity seems to him beset with extraordinary difficulties, 

 by adopting the undulatory theory of light. The subject of 

 the combined or latent caloric of bodies, and the circumstance 

 of transparent solid bodies belonging entirely to the class of 

 electrics, give him a presentiment that we must look to more 

 varied and profound causes than the motion of a subtile aether 

 for the explanation of the effects we witness. (I must here 

 notice that I cannot, with many opticians, call the translucency 

 of thin metallic leaves transparency.) The phenomena of the 

 absorption of light by coloured media have justly been shown 

 by Sir David Brewster to militate strongly against this theory. 

 My own discovery of the law of reflection by metals offers also 

 a strong objection ; for that whilst a considerable portion of 

 the light enters the substance of the metal as in transparent 

 bodies, yet the law of the variation of the intensity of the re- 

 flection is essentially different. The chemical theory would 

 remind us that both classes of bodies possess determinate 

 specific heats, but that there is an essential difference in their 

 electrical properties, the former being conductors, and the 

 latter electrics. I hence learn to look beyond the results of a 

 mechanical theory on the motions excited in a subtile aether, 

 for the solution. The effects of chemical agency and of ar- 

 rangement of atoms in crystallized bodies show also the con- 

 nexion of the optical effects with chemical affinities, and which 

 brings us again to the theory of chemical combinations, with- 

 out which, it appears to me, we can never give a satisfactory 

 reason for double refraction, which is so intimately connected 

 with the polarized condition of light. 



The failing of the deductions of the most talented men who 

 have adopted the undulatory theory, of which many instances 

 have fallen under my own observation, and several of which 

 I have already published, give me also more than a distrust 

 of the fundamental hypothesis having any basis in nature. 



With respect to the claim of half an undulation, my manner 

 of speaking of which appears unpleasant to Professor Airy, I 

 must say, that, although we do not find any mention of it 

 under this title in his undulatory theory of optics in the last 

 edition of his mathematical tracts, yet he is no doubt aware 

 that when he says " he must have derived it from some very 

 imperfect or erroneous statement," I had in recollection 



