Prof. L. Moser on the so-called Calorotypes. 357 



ployed forms a great objection to this view of the subject. It was there- 

 fore necessary to try whether the same phenomena could not be pro- 

 duced without the application of heat, and in this I succeeded." [Scien- 

 tific Memoirs, vol. iii. p. 443.] 



In the Addendum to this Memoir [Scient. Mem. vol. iii. 

 p. 459], in which I advanced the hypothesis that the depict- 

 ing of the bodies wa6 due to a light proper to themselves, I 

 have spoken of the auxiliary influence of heat in such a man- 

 ner as will I hope settle this point. Bodies become luminous 

 when heated ; that is, they emit light of the refrangibility of 

 ordinary light. After this it will hardly be admitted that this 

 emission of light takes place suddenly; besides, the experi- 

 ments prove the contrary; they show that light is radiated at 

 all temperatures from bodies, that its intensity increases and 

 its refrangibility decreases as the temperature becomes higher. 

 According to my experiments the invisible rays of light pass 

 very readily through aqueous solutions of various kinds, and 

 through different oils, but they decidedly do not pass through 

 the thinnest plates of glass, mica, amber or rock salt. [I have 

 only recently made some experiments with the latter sub- 

 stance.] But if the temperature be raised, they pass very 

 readily both through glass and mica, which is perfectly in 

 accordance with the supposition that their intensity is increased 

 and their refrangibility approximated to those of visible light. 

 [Substances such as white glass, mica, &c., consequently lose 

 the character of perfect transparency ; they retain it only for 

 a certain group of rays of light.] 



Should it be concluded from the influence of heat on light, 

 — corresponding so closely in its other properties to other phy- 

 sical forces, — that light and heat are identical, then let us see 

 further on how the remaining phaenomena are to be explained. 

 I would merely impress on the reader not to be led astray 

 by the mass of proofs which might perhaps be enumerated in 

 favour of such an identity ; they are all of them nothing more 

 than variations upon the old fact of the incandescence of bo- 

 dies at an elevation of temperature. With this I may at 

 present take my leave of Mr. Hunt; the very title of his 

 paper conveys the opinion of its being dependent on the in- 

 fluence of heat, and he has not even entered into the subject 

 so far as he read it in my first Memoir. As I have stated 

 above, he has not devised a single new experiment, for even 

 those which appear to him sufficiently important to be adopted 

 as the running head to his paper, " Art of copying engravings 

 from paper on metallic plates by means of heat," will be found 

 nearly word for word in these A?male?i > vol. lvii. p. 570*. 



* Published in 1842. 



