A Manual Of Photography

THERMOGRAPHY. 169 could not be detected to leave any evidence of action, and as spectra imprinted on pliotographic 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 Maga- zine for October 1840, I mentioned some instances in which I had copied printed paper and engravings on iodized paper by mere contact and exposure to the influence of calorific rays, or to artificial heat. 1 then, speculating on the probability of our being enabled, by some such process as the one I then named, to copy pictures and the like, proposed the name of Thermo- graphy, to distinguish it from Photography. 18. I now tried the effects of a print in close contact with a well-polished copper plate. When exposed to mercury, I found that the outline was very faithfully copied on the metal. 19. A paper ornament was pressed between two plates of glass, and warmed; the impression was brought out with tolera- ble distinctness on the under and warmest glass, but scarcely traceable on the other. 20. Bose leaves were faithfully copied on a piece of tin plate, exposed to the full influence of sunshine ; but a much better impression was obtained by a prolonged exposure in the dark. 21. With a view of ascertaining the distance at which bodies might be copied, I placed upon a plate of polished copper a thick piece of plate-glass, over this a square of metal, and several other things, each being larger than the body beneath. These were all covered by a deal box, which was more than half an inch distant from the plate. Things were left in this position for a night. On exposing to the vapour of mercury, it was found that each article was copied, the bottom of the deal box more faith- fully than any of the others, the grain of the wood being imaged on the plate. 22. Having found, by a series of experiments, that a black- ened paper made a stronger image than a white one, I very anxiously tried to effect the copying of a printed page or a print. I was partially successful on several metals ; but it was not until 1 used copper plates amalgamated on one surface, and the mercury brought to a very high polish, that I produced anything of good promise. By carefully preparing the amalga- mated surface of the copper, I was at length enabled to copy from paper, line-engravings, woodcuts, and lithographs, with surprising accuracy. The first specimens produced exhibited a minuteness of detail and sharpness of outline quite equal to