1839.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



103 



a goad imajje of my object upon prepared paper, on returning at the expira- 

 tion of an liour I found that no eflfect liaj taken place. I was therefore half 

 inclined to abandon this experiment, when it occurred to me that there was no 

 reason to suppose that the common muriate of silver was the most sensitive 

 substance that exists to the action of the chemical rays ; and though such should 

 eventually prove to be the fact, at any rate it was not to be assumed without 

 proof. I therefore began a course of experiments in order to ascertain the 

 inrtueuce of various modes of preparation, and I found these to be signally 

 different in their results. I considered this matter cliietly in a practical point 

 of view ; for as to the theory, I confess that I cannot as yet understand the 

 reason why the paper prepared in one way should be so much more sensitive 

 than in another. 



The result of these experiments was the discovery of a mode of preparation 

 greatly superior in sensibility to what I had originally employed; and by 

 means of this, all those etl'ecti which 1 had before only anticipated as theoreti- 

 cally possible were found to be capable of realization. 



With a sheet of this, which I shall call " Sfinilire Pujifr," is placed in a 

 dark chamber, anil the magnified image of some object thrown on it by the 

 solar microscope, after the lapse of ])erhaps a quarter of an hour, the picture is 

 found to be completed. I Inve not as yet used high magnifying powers, on 

 account of the consequent enfeeblement of the light. Of course with a more 

 sensitive paper, greater magnifying power will become desirable. 



On examining one of these pictures, which I made about three years and S0 

 half ago, I find, by actual measurement of the picture and the object, that the 

 latter is magnitied seventeen times in linear diameter, and in surface conse- 

 quently 2y'J times. I have others which I believe are considerably more 

 magnified ; but I have lost the corresponding objects, so that 1 cannot here 

 atate the exact numbers. 



Not only does this process save our time and trouble, but there are many 

 objects, especially microscopic crystallizations, which alter so greatly in the 

 course of three or four days (and it could hardly take any artist less to delineate 

 them in all their details,) that they could never be drawn in the usual way. 



I will now de>^cribe the degrcf ul ^eniilirt'iit'is which this paper possesses, 

 premising that I am far from supposing that I have reached the limit of which 

 this quality is capable. On the contrary, considering the few experiments 

 which ! have made, (few, that is, in comparison with the number which it would 

 be easy to imagino and propose) I think it most likely that other methods may 

 be found, by which substances may be prepared, perhaps as much transcending 

 in sensitiveness the one which I have employed, as that does the ordinary state 

 of the nitrate of silver. But to continc myself to what 1 have actually accom- 

 plished in the preparation of a very sensitive paper. 



When a sheet of paper is brought towards a window, not one through which 

 the sun sliines, but looking in the opposite direction, it immediately begins to 

 discolour. For this reason, if the paper is prepared by daylight, it must by no 

 means lie left uncovered, but as soon as Buished be shut up in a drawer or cup- 

 board and there left to dry, or else dried at night by the warmth of a lire. 

 Before using this paper for the delineation of any object, 1 generally approach 

 it for a little time towards the light, thus intentionally giving it a slight shade 

 of colour, for the |>urpose of seeing that the i/nnt/ui is i-i'fn. If it appears so 

 when thus tried to a small extent, it will generally be found to prove so in the 

 final result. But if there are some places or spots in it which do not acquire 

 the same tint as the rest, such a sheet of pai)er should be rejected; for there is 

 a risk that, when employed, instead of presenting a ground uniformly dark, 

 which is essential to the beauty of the drawing, it will liave laige wh'te spots, 

 places altogether insensible to the ell'ect cif light. Thi^ singular circumstance 

 I shall revert to elsewhere; it is sufficient to mention it here. 



The paper then, which is thus readily sensitive to the light of a common 

 window, is of course much more so to the direct sanshine. Indeed, such is the 

 velocity of the effect then produced, that the picture may be said to be ended 

 almost as soon as it is begun. 



To give some more definite idea of the rapidity of the process, I will state, 

 that after various trials the nearest evaluation which I could make of the time 

 necessary for obtaining the picture of an object, so as to have pretty distinct 

 outlines, when I employed the full sunshine, was /ici// « svcuml. 



9. An-hitectio'e, LfimUctipe,and E.tlvr/tal iVuturc. — But perhaps the most 

 curious application of this art is the one I am now about to relate. At least 

 it is that which has appeared the most surprising to those who have examined 

 my collection of pictures formetl by solar light. 



Every one is acquainted with the beautiful effects which are produced by a 

 cimera obscura, and has admired the vivid picture of external nature which it 

 displays. It had often occurred to me, that if it were possible to retain upon 

 the paper the lovely scene which thus illuminates it for a moment, or if we 

 could but Hx the outline of it, the lights and shadows divested of all iuluitr, 

 such a result could not fail to be most interesting. And however much I might 

 be disposed at lirst to treat this notion as a scientific dream, yet when 1 had 

 succeeded in fixing the images of the solar niicroscope by means of a peculiarly 

 sensitive paper, there appeared no longer any doubt that an analogous process 

 would succeed in copying the objects of external nature, although indeed they 

 are much less illuminated. 



Not having with me in the country a camera obscura of any considerable 

 size, I constructed one out of a lari^e box, the image being thrown upon one 

 end of it by a good object glass iixed in the opposite end. This apparatus 

 being armed with a sensitive paper was taken out in a summer afternoon and 

 placed about one hundred yards from a building favourably illuminated by the 

 sun. An hour or two afterwards I opened the box, and 1 found depicted upon 

 the paper a very distinct representation of the building, with the exception of 

 those parts of it which lay in the shade. A little experience in this branch of 

 the art showed me that with smaller camcrii) obseurro tb* vtiW\ \\m\\d hti uj-q. 



No, IB.— ftUncH, 1839. Vol. {I. 



duced in a smaller time. Accordingly 1 had several small boxes made, in which 

 1 fixed lenses of shorter focus, and with these I obtained very perfect but 

 extremely small pictures ; such as without great stretch of imagination n.igbt 

 bo supposed to be the work of some Lilliputian artist. They requite indeed 

 examination with a lens to discover all their miimliK. 



In the summer of I83j I made in this way a number of representations of 

 my house in the country, which is well suited to the purpose, froiu its ancient 

 and remarkable architecture. And this building 1 believe to be the first that 

 was ever yet known ht huiw drtin-n ih uirn jihIui-l'. 



The method of proceeding w.as this ; having first adjusted the paper to the 

 proper focus in each of these little camei;e, I then took a number of them with 

 mc out of doors and placed them in different situations around the building. 

 After the lapse of half an hour I gathered them all up, and brought them 

 within doors to open them. When opened, there was found in each a minia- 

 ture picture of the objects before which it had been placed. 



To the traveller in distant lands who is ignorant, as too many unfortunately 

 are, of the art of drawing, this little invention ni.ay prove of real service ; and 

 even to the artist himself, however skilful he may be. For although this 

 natural process does not produce an efl'.ct much resembling the productions of 

 his pencil, and therefore cannot be considered as capable of replacing them, yet 

 it is to be recollected that he may often be so situated as to be able to devote 

 only a single hour to the delineation of some very interesting locality. Now, 

 since nothing prevents him from simultaneously disposing, in different positions, 

 any number of these little caiiiei-a; it is evident that their collective results 

 when examined afterwards, may furnish him with a large body of interesting 

 memorials, and with numerous details which he had not had himself time either 

 to note down or to delineate. 



10. DeliiinUhiiix of Sculiilun Another use which I propose to make of my 



invention is for the copying of statues and bas reliefs. I place these in strong 

 sunshine, and put before them at a proper distance, and in the requisite 

 position, a small camera obscura containing the prepared paper. In this way 

 I have obtained images of various statues. Ike. I have not pursued this branch 

 of the suiiject to any extent : but 1 expect interesting results from it, and that 

 it may be usefully employed under many circumstances. 



11. Coin/ill,/ al' EiKjmruujs. — The invention may he employed with great 

 facility for obtaining copies of drawings or engravings or facsimiles of MSS. 

 For this purpose the engraving is pressed upon the prepared paper, with its 

 engraved side in contact with the latter. The pressure must be as uniform as 

 possible, that the contact may be perfect ; for the least interval sensibly 

 injures the result, by producing a kind of cloudiness in lieu of the sharp strokes 

 of the original. 



When placed in the sun, the solar light gradually traverses the paper, 

 except in those places wheie it is prevented from doing so by the opaque lines 

 of the engraving. It therefore of course makes an exact image or print of the 

 design. This is one of the experiments which Davy and Wedgwood state that 

 they tried, but failed, from want of sufficient sensibility in their paper. 



The length of time requisite for effecting the copy depends on the thickness 

 of the paper on which the engraving bas been printed. At first I thought 

 that it would not be possible to succeed with thick papers ; but I found on 

 trial that the success of the method was by no means so limited. It is enough 

 for the purpose, if the paper allows any of the solar light to pass. When the 

 paper is thick, I allow half an hour for tile formation of a good copy. In this 

 way I have copied very minute, complicated, and delicate engravings, crowded 

 with figures of small size, which were rendered with great distinctness. 



The effect of the copy, though of course unlike the original, (substituting as 

 it does lights for shadows, and rice rersn), yet is often very pleasing, and would, 

 I think, suggest to artists useful ideas respecting light and shade. 



It may be supposed that the engraving would be soiled or injured by being 

 thus pressed against the prepared paper. There is not much danger of tljis, 

 provided both are perfectly dry. It may be well to mention, however, that in 

 case any stain should be perceived onthe engraving, it may be readily removed 

 by a chemical application which does no injury whatever to the paper. 



In copying engravings, &c. , by this nicihod. the lights and shadows are 

 reversed, consequently the effect is wholly altered, lint if the picture so^ 

 obtained is first pfrsrfpinl so as to bear sunshine, it may be afterwards itselt 

 employed as an object to be copied ; and by means of this second process the 

 lights and sh.adows are brought back to their original disposition. In this way 

 we have indeed to contend with the imperfections arising frmu two processes 

 inste.ul of one ; but I believe this will be found merely a difficulty of manipu- 

 lation. I propose to employ this for the purpose more particularly of 

 multiplying .at small expense copies of such rare or unique engravings as it 

 would not be worth while to re-engrave, from the limited demand for them. 



I will now add a few remarks concerning the very singular circumstance, 

 which I have before brielly mentioned, viz. that the paper sometimes, alihough 

 intended to be prepared of the most sensitive quality, turns out on trial to be 

 wholly insensible to light, and incapable of change. The most singular part 

 of this is the very small difference in tlie mode of preparation which causes so 

 wide a discrepancy in the result, b'or instance, a sheet of paper is all prepared 

 at the same time, and with the intention of giving it as much uniformity as 

 possible; and yet, when exposed to sunshine, this paper will exhibit large 

 white spots of very detinite outline, where the piepariiig process has tailed: 

 the rest of the paper, where it has succeeded, turning idaek as rapidly as 

 possible. Sometimes the spots are of a pale tint of cierulean blue, and are 

 surrounded by exceedingly definite outlines of perfect whiteness, contrasting 

 very much with the blackness of (he part immedi.ately succeeding. With 

 reg.ard to the theory of this, I am only prepaied to state as my opinion at 

 present, that it is a case of what is called " unstable equilibrium." The 

 [jvoccss followed is such »i to pvodure one uf two definite ciieinical compounds ; 



