and on the recent discovery of Moser. 465 



marked out, showing some relation to exist between the sub- 

 stances used and the vapours applied. 



12. Placed the glasses used above (9, &c.) with a piece of 

 well-smoked glass for half an hour, one-twelfth of an inch be- 

 low a polished plate of copper. The vapour of mercury 

 brought out the image of the smoked glass only. 



.13. All these glasses were placed on the copper and slightly 

 warmed ; red and smoked glasses gave after vaporization, 

 equally distinct images, the orange the next ; the others left but 

 faint marks of their forms ; polishing with Tripoli and putty 

 powder would not remove the images of the smoked and red 

 glasses. 



14. An etching, made upon a smoked etching ground on 

 glass, the copper and glass being placed in contact. The 

 image of the glass only could be brought out. 



15. A design cut out in paper was pressed close to a cop- 

 per plate by a piece of glass, and then exposed to a gentle 

 heat j the impression was brought out by the vapour of mer- 

 cury in beautiful distinctness. On endeavouring to rub off 

 the vapour, it was found, that all those parts which the paper 

 covered, amalgamated with mercury, which was removed from 

 the rest of the plates ; hence there resulted a perfectly per- 

 manent white picture on a polished copper plate. 



16. The coloured glasses before named (9, 12) were placed 

 on a plate of copper with a thick piece of charcoal, a copper 

 coin, the mica and the paper, and exposed to a fervent sun- 

 shine. Mercurial vapour brought up the images in the fol- 

 lowing order: smoked glass, crown glass, red glass, mica beau- 

 tifully delineated, orange glass, paper, charcoal, the coin, blue 

 glass ; thus distinctly proving that the only rays which had 

 any influence on the metal, were the calorific rays. This ex- 

 periment was repeated on different metals, and with various 

 materials, the plate being exposed to steam, mercury and 

 iodine; I invariably found that those bodies which absorbed 

 or permitted the permeation of the most heat gave the best 

 images. The blue and violet rays could not be detected to 

 leave any evidence of action, and as spectra imprinted on pho- 

 tographic papers by light, which had permeated these glasses, 

 gave evidence of the large quantity of the invisible rays which 

 passed them freely, we may also consider those as entirely 

 without the power of effecting any change on compact simple 

 bodies. 



17. In a paper which I published in the Philosophical 

 Magazine for October 1840, I mentioned some instances in 

 which I had copied printed pages and engravings on iodized 

 paper, by mere contact and exposure to the influence of the 



Phil. Mag. S. 3. Vol. 21. No. 140. Dec. 1842. 2 I 



