1843.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



2] 



results were as before (3, 4). On rubbing off the vapour, it was found that 

 the gold and silver had made permanent impressions on the copper. 



6. The above being repeated with a still greater heat, the image of the 

 copper coin was, as well as the others, most faithfully given, but the gold 

 lead, and silver only made permanent impressions. 



7. A silvered copper plate was now tried with a moderate warmth (3). 

 Mercurial vapour brought out good images of the gold and copper; the 

 silver marked, but not well defined. 



8. Having repeated the above experiments many times with the same 

 results. I was desirous of ascertaining if electricity had any similar effect: 

 powerful discharges were passed through and over the plate and discs, and 

 it was subjected to a long continued current without any effect. The silver 

 had been cleaned off from the plate (7), it was now warmed with the coins 

 and medals upon it, and submitted to discharges from a very large Leyden 

 jar ; on exposing it to mercurial vapour, the impressions were very prettily 

 brought out, and strange to say, spectral images of those which had been 

 received on the plate when it was silvered (7). Thus proving that the influ- 

 ence, whatever it may be, was exerted to some depth in the metal. 



9. I placed upon a plate of copper, blue, red. and orange coloured glasses, 

 pieces of crown and flint glass, mica, and a square of tracing paper. These 

 were allowed to remain in contact half an hour. The space occupied by the 

 red glass was well marked, that covered by the orange was less distinct, but 

 the blue glass left no impression : the shapes of the flint and crown glass 

 were well made out, and a remarkably strong impression where the crown 

 glass rested on the tracing paper, but the mica had not made any impression. 



10. The last experiment repeated ; after the exposure to mercurial vapour, 

 heat was again applied to dissipate it, the impression still remained. 



11. The experiment repeated, but the vapour of iodine used instead of that 

 of mercury. The impressions of the glasses appeared in the same order as 

 before, but also a very beautiful image of the mica was developed, and the 

 paper well 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 below a polished plate of cop- 

 per. The vapour of mercury brought out the imago 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 copper plate by a piece 

 of glass, and ihen exposed to a gentle heat ; the impression was brought out 

 by the vapour of mercury 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 permanent white picture on a polished cop- 

 per plate. 



1C. 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 fervent sunshine. Mercurial vapour brought up the 

 images in the following order — smoked glass, crown glass, red glass, mica 

 beautifully 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 experiment, was repeated on different 

 metals, and with various materials, the plate being exposed to steam, mer- 

 cury, 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 photographic 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. 1 mentioned some instances in which I had copied printed pages and 

 engravings on iodized paper, b mere contact and exposure to the influence 

 of the calorific rays, or to artificial heat. I then, speculating on the proba- 

 bility of our being enabled, by some such process as the one I then named, to 

 copy pictures and the like, proposed the name of Thermography, to distin- 

 guish 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 tolerable distinctness on the 

 under and warmest glass, but scarcely traceable on the other. 



20. Rose leaves were faithfully copied on a piece of tin plate, ex] 



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 plat,' 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 faithfully than anv of 

 the others, the grain of the wood being imaged on (he plate. 



22. Having found, by a series of experiments, that a blackened paper made 

 a stronger image than a white one, I very anxiously tried to effect the copy- 

 ing of a printed page or a print. 1 was partially successful on several 

 metals, but it was not until I used copper plates amalgamated on one sur- 

 face, and the mercury brought to a very high polish, that 1 produced any 

 thing of good promise. By carefully preparing the amalgamated surface of 

 the copper, I was at length enabled to copy from paper line-engravings, 

 wood-cuts, and lithographs, with surprising accuracy. The first specimens 

 produced (which were submitted to inspection), exhibit a minuteness of de- 

 tail and sharpness of outline quite equal to the early Daguerreotypes and the 

 photographic copies, prepared with chloride of silver.' 



The following is the process at present adopted by me, which I con- 

 sider far from perfect, but which affords us very delicate images. A well 

 polished plate of copper is rubbed over with the nitrate of mercury, and then 

 well washed to remove any nitrate of copper which may be formed ; when 

 quite dry, a little mercury taken up on soft leather or linen is well rubbed 

 over it, and the surface worked to a perfect mirror. The sheet to be copied 

 is placed smoothly over the mercurial surface, and a sheet or two of soft, 

 clean paper being placed upon it, is pressed into equal contact with the 

 metal by a piece of glass, or flat board; in this state it is allowed to remain 

 for an hour or two. The time may be considerably shortened by applying a 

 very gentle heat for a few minutes to the under surface of the plate. The 

 heat must on no account be so great as to volatilize the mercury. The next 

 process is to place the plate of metal in a closed box, prepared for generating 

 the vapour of mercury. The vapour is to be slowly evolved, and in a few 

 seconds the picture will begin to appear ; the vapour of mercury attacks 

 those parts which correspond to the white parts of the printed page or en- 

 graving, and gives a very faithful but somewhat indistinct image. The plate 

 is now removed from the mercurial box. and placed in one containing iodine, 

 to the vapour of which it is exposed for a short time ; it will soon be very 

 evident that the iodine vapour attacks those parts which are free from mer- 

 curial vapour, blackening them. Hence there results a perfectly black pic- 

 ture, contrasted with the grey ground formed by the mercurial vapour. The 

 picture being formed by the vapours of mercury and iodine, is of course in 

 the same state as a Daguerreotype picture, and is readily destroyed by 

 rubbing. From the depth to which I find the impression made into the 

 metal, I confidently hope to be enabled to give to these singular and beauti- 

 ful productions a considerable degree of permanence, so that they may be 

 used by engravers for working on. It is a curious fact, that the vapoars of 

 mercury and of iodine attack the plate differently, and I believe it will be 

 found that vapours have some distinct relation to the chemical or thermo- 

 electrical state of the bodies upon which they are received. Moser has ob- 

 served this, and attributes the phenomena to the colours of the rays, which 

 he supposes to become latent in the vapour on its passing from the solid into 

 the more subtile form. I do not, however, think this explanation will agree 

 with the results of experiments. I feel convinced that we have to deal with 

 some thermic influence, and that it will eventually be found that some purely 

 calorific excitement produces a molecular change, or that a thermo-electric 

 action is induced, which effects some change in the polarities of the ultimate 

 atoms of the solid. 



These are matters which can only be decided by a series of well conducted 

 experiments. Although attention was called to the singular manner in 

 which vapours disposed themselves on plates of glass and copper, two years 

 since by Dr. Draper, Professor of Chemistry at New York, and about the 

 same time to the calorific powers of the solar spectrum, by Sir John Her- 

 schel, and to the influence oi heat artificially applied, by myself 1 17). yet it 

 is certainly due to M. Moser of Konigsberg. to acknowledge him to be the 

 first who has forcibly called the attention of the scientific world to an in- 

 quiry which promises to be as important in its results as the discovery of the 

 electric pile, by Volta. 



' The first faithful copy of the lines of a copper plate engi 

 tained by Mr. Cautabrana, who has since succeeded in procuring some tole- 

 rable specimens on amalgamated copper which cannot be rubbed oil. 



