200 Mr. Talbot's Account ofihe 



was a good i-epresentation ? when the reply was, " That they 

 were not to be so easily deceived, for that it was evidently no 

 picture, but the piece of lace itself." 



At the very commencement of my experiments upon this 

 subject, when I saw how beautiful were the images which 

 were thus produced by the action of light, I regretted the 

 more that they were destined to have such a brief existence, 

 and I resolved to attempt to find out, if possible, some me- 

 thod of preventing this, or retarding it as much as possible. 

 The following considerations led me to conceive the possi- 

 bility of discovering a preservative process. 



The nitrate of silver, which has become black by the action 

 of light, is no longer the same chemical substance that it was 

 before. Consequently, if a picture produced by solar light is 

 subjected afterwards to any chemical process, the white and 

 dark parts of it will be differently acted upon ; and there is 

 no evidence that after this action has taken place, these white 

 and dark parts will any longer be subject to a spontaneous 

 change; or, if they are so, still it does not follow that that 

 change will 7101x1 tend to assimilate them to each other. In 

 case of their remaining diisimilai; the picture will remain vi- 

 sible, and therefore our object will be accomplished. 



If it should be asserted that exposure to sunshine would 

 necessarily reduce the whole to one uniform tint, and destroy 

 the picture, the onus probandi evidently lies on those who 

 make the assertion. If we designate by the letter A the ex- 

 posure to the solar light, and by B some indeterminate che- 

 mical process, my argument was this : Since it cannot be 

 shown, a priori, that the final result of the series of processes 

 ABA will be the same with that denoted by B A, it will 

 therefore be worth while to put the matter to the test of ex- 

 periment, viz, by varying the process B until the right one be 

 discovered, or until so many trials have been made as to pre- 

 clude all reasonable hope of its existence. 



My first trials were unsuccessful, as indeed I expected ; 

 but after some time I discovered a method which answers 

 perfectly, and shortly afterwards another. On one of these 

 more especially I have made numei'ous experiments; the 

 other I have comparatively little used, because it appears to 

 require more nicety in the management. It is, however, 

 equal, if not superior, to the first in brilliancy of effect. 



This chemical change, which I call the preserving process, 

 is far more effectual than could have been anticipated. The 

 paper, which had previously been so sensitive to light, becomes 

 completely insensible to it, insomuch that I am able to show 

 the Society specimens which have been exposed for an hour 



