THE BEGINNINGS OF PHOTOGRArHY. 359 



resumed about this date or in 1800. Writing- to T. Wedgwood in 

 Novem])er, 1800, Leslie mentions an object glass for the solar micro- 

 scope and some painted glass which had been left for him at the 

 W^edgwood House, in York street, St. James square, and Wedgwood 

 came to town about the same time. Davy could not have taken part 

 in these experiments, l)ecause he was still at Bristol, but they w^ere 

 old acquaintances, and Davy may have advised him. In Wedgwood's 

 earlier experiments of 1790 he no doubt had the assistance of Chisholm, 

 who, as we have seen alread}^ knew a good deal about the reduction 

 of silver and other metals by light. Davy mentions in the paper pub- 

 lished in the Journal of the Royal Institution for 1802 that to cop3^ 

 the images formed by means of a camera obscura was Wedgwood's 

 first object in his researches, and for this purpose he used the nitrate 

 of silver, which was mentioned to him by a friend as a substance ver}" 

 sensible to the influence of light, but the images thus formed in the 

 camera were too faint to produce any effect on the nitrate of silver, 

 and all his numerous experiments to this primary end proved un- 

 successful. 



From the scanty details of the experiments given b}^ Davy in this 

 paper it is very difficult to ascertain clearl}^ the relative share that 

 Wedgwood and Davy had in producing the results obtained. It is 

 evident from the above that the idea of reproducing the images formed 

 in the camera obscura was Wedgwood's own, for he had been familiar 

 with the use of it from his youth, and his first experiments were no 

 doubt made with paper washed over with a solution of silver nitrate. 

 For certain sul)jects, copjdng paintings on glass, or making delinea- 

 tions of objects parth^ opaque and parti}" transparent in texture, such 

 as leaves, or wings of insects, etc., white leather was found preferable 

 to paper, because it was more sensitive, the tanned gelatine no doubt 

 acting as an accelerator. Davy, however, says that in following 

 these processes he found that the images of small objects produced 

 by the solar microscope might be copied without difficult}^ on paper, 

 but it was necessary that the paper should be but a small distance 

 from the lens. He notes also that the muriate of silver was more sen- 

 sitive than the nitrate and both were more readily acted on when 

 moist than when dry, a fact long known. The advantage of the nitrate 

 was its s()lul>ility, but leather or paper could ])e impregnated with the 

 muriate by diffusing it through water and applying it in this form 

 (as Hitter did) or by immersing paper moistened with the solution of 

 the nitrate in very dilute nuiriatic acid. 



In dis(;ussing the difficulty of preventing the uncolorcd parts of the 

 copies or profiles from being acted on by light, even after repeated 

 washings, on account of some of the saline matter still adhering to the 

 white parts of the paper or leather and causing them to darken on 

 exposure to the sun, he says, "It is probable that both in the case of 

 SM 1903 24 



