in reply to his Animadversions. 417 



Now, with regard to the experiments themselves, surely 

 Professor Moser will not claim as his own the experiments, of 

 placing a coin on a glass or polished metal plate, or of writing 

 on glass with a piece of steatite, and bringing out the images 

 by breathing on them. Dr. Draper in 1840 published this*; 

 and when a schoolboy, twenty years ago, I tried these expe- 

 riments without ever suspecting their scientific value, which 

 M. Moser was the first to call attention to. M. Moser, in 

 his memoir ' On the Action of Light on Bodies,' states, 

 ** Silver and other metallic plates were made warm, and cold 

 bodies, variously cut stones, figures of horn, pasteboard, cork, 

 coins, &c. allowed to remain on them for some time." It 

 must be distinctly understood, that at the meeting of the 

 British Association it was stated, that the images could be 

 brought out by the vapours of water, mercury, &c; but with- 

 out being, at the period of making my experiments, October 



1842, aware of the above, which I did not see until February 



1843, my first simple experiments convinced me that some 

 connexion existed between the conducting powers of bodies, 

 as it regards heat, and the strength of the impressions made by 

 them. With this in view I tried good and bad conductors of 

 heat, from copper plates and coins to platina ones, glass and 

 charcoal. These constitute the experiments given in para- 

 graphs from 2 to 7 of my paper. Now if M. Moser used all 

 these materials, and I do not doubt but he may have done so, 

 he certainly did not make his experiments with the same ob- 

 ject in view, or he would not have neglected to observe the 

 fact, which I was the first to announce, that " bodies which 

 are bad conductors of heat placed on good conductors make de- 

 cidedly the strongest impressions." I am quite ready to give 

 up any claim to the experiments, but I reserve to myself the 

 interpretation they afford. 



M. Moser says, " I cannot name a single experiment, &c. 

 &c. which I had not previously described." Will M. Moser 

 oblige by directing me to any of his memoirs, where may be 

 found the experiments named in paragraph 8, which show the 

 power of electrical discharges in evoking again these mysteri- 

 ous images after they have been effaced ? Or that in paragraph 

 15, where a copper plate is described to have been so changed 

 in its molecular constitution, by being warmed in contact with 

 a piece of paper, that it readily amalgamated with mercury 

 over the parts which the paper covered, but not so over the 

 other portions of the plate? 



Nearly all the other paragraphs of my paper, to the 22nd, 

 are details of experiments with coloured glasses and transpa- 

 rent bodies, placed upon plates of unprepared copper and 

 • In Phil. Mag., S. 3, vol. xvii. p. 217.— Edit. 



Phil. Mag. S, 3. Vol. 23. No. 154. Dec. 1843. 2 E 



