418 Mr. Hunt on the Spectral Images of M. Moser, 



silver. I find that M. Moser has also used coloured glasses, 

 but principally upon iodized silver plates. It is to be lamented 

 that he has made so great a number of very careful experi- 

 ments in this way; for, by regarding the colour of the glass, 

 and the colour of. the ray which permeates it, as the same, he 

 has been led to some very incorrect conclusions, as the slight- 

 est acquaintance with the valuable labours of Sir John Her- 

 schel would have shown him. My use of coloured glasses in 

 these experiments was confined to the heating powers of the dif- 

 ferent colours, and these were contrasted with smoked glasses, 

 and the like, the results showing, whether the experiments 

 were made in sunshine or at night, that those glasses, the red 

 and blackened ones, which admitted the permeation, or ab- 

 sorbed the largest quantity of heat, made the most decided 

 impressions on metal plates. I cannot see how M. Moser 

 makes out his claim to these experiments, except it is upon 

 the principle that Professors Faraday and Daniell are guilty of 

 scientific piracy in publishing, in their valuable memoirs, re- 

 sults obtained with zinc and copper plates, Volta having used 

 the same kind of plates before them. 



I have only to deal with one more of Professor Moser's 

 charges. He says, " He has not devised a single new experi- 

 ment, for even those which appear to him sufficiently import- 

 ant to be adopted as the running head of his paper, ' The art 

 of copying engravings, or any printed characters from paper 

 on metal plates,' will be found nearly word for word in the 

 Annalen, vol. lvii. p. 570." The latest memoir of M. Moser 

 with which I am acquainted, is the 18th article in the 3rd vol. 

 of the Scientific Memoirs, which is stated to be "from Pog- 

 gendorfF's Annalen, Band lvii., 1842, No. 9. p. 1." I presume 

 M. Moser alludes to a more recent publication. He, how- 

 ever, relieves me from a difficulty by saying, "It is that expe- 

 riment in which I caused a seal to depict itself on mercury with 

 which a pure or silvered copper-plate had been coated, and af- 

 terwards produced the image in the iodine vapours." Now we 

 will examine the similitude between this and my published ex- 

 periment. A copper plate is amalgamated by nitrate of 

 mercury, and a line or mczzotinto engraving, a wood-cut or li- 

 thographed print, on paper, is placed upon it for a few hours. 

 With certain precautions the plate is exposed to the vapour 

 of mercury, this vapour attacks those parts of the plate which 

 correspond with the white parts of the paper, and a faint image 

 is formed ; the plate is now placed in the iodine box for a little 

 time, and its vapour attacking and blackening those parts of 

 the plate, which correspond with the dark portions of the 

 paper, brings out a very decided and beautiful copy of the 

 print. I am quite satisfied to leave it to yourselves and your 

 readers to say if this "sufficiently important" experiment is 



