Art of Photogenic Drawing. 197 



to purposes of utility the very curious property which has 

 been long known to chemists to be possessed by the nitrate 

 of silver ; namely, its discoloration when exposed to the violet 

 rays of light. This property appeared to me to be perhaps 

 capable of useful application in the following manner. 



I proposed to spread on a sheet of paper a sufficient quan- 

 tity of the nitrate of silver, and then to set the paper in the 

 sunshine, having first placed before it some object casting a 

 well-defined shadow. The light, acting on the rest of the 

 paper, would naturally blacken it, while the parts in shadow 

 would retain their whiteness. Thus I expected that a kind 

 of image or picture would be produced, resembling to a cer- 

 tain degree the object from which it was derived. I expected, 

 however, also, that it would be necessary to preserve such 

 images in a portfolio, and to view them onl^' by candle-light ; 

 because if by daylight, the same natural process which form- 

 ed the images would destroy them, by blackening the rest of 

 the paper. 



Such was my leading idea before it was enlarged and cor- 

 rected by experience. It was not until some time after, and 

 when 1 was in possession of several novel and curious results, 

 that I thought of inquiring whether this process had been 

 ever proposed or attempted before? I found that in fact it 

 had ; but apparently not followed up to any extent, or with 

 much perseverance. The few notices that I have been able 

 to meet with are vague and unsatisfactory ; merely stating 

 that such a method exists of obtaining the outline of an ob- 

 ject, but going into no details respecting the best and most 

 advantageous manner of proceeding. 



The only definite account of the matter which I have been 

 able to meet with, is contained in the first volume of the Jour- 

 nal of the Royal Institution, page 170, from which it appears 

 that the idea was originally started by Mr. Wedgwood, and 

 a numerous series of experiments made both by him and Sir 

 Humphry Davy, which however ended in failure. I will take 

 the liberty of quoting a few passages from this memoir. 



" The copy of a painting, immediately after being taken, 

 must be kept in an obscure place. It may indeed be ex- 

 amined in the shade, but in this case the exposure should be 

 only for a few minutes. No attempts that have been made to 

 prevent the uncoloured parts from being acted upon by light, 

 liavc as yet been successful. They have been covered with 

 a thin coating of fine varnish; but this has not destroyed their 

 susceptibility of becoming coloured. When the solar rays 

 are passed through a piint and thrown upon prepaied paper. 



