Miscellanies. 171 



In the spring of 1834, Mr. Talbot began a series of experiments, with 

 the hope of turning to useful account the singular susceptibility evinced 

 by the nitrate of silver when exposed to the rays of a powerful light; but 

 not being acquainted with the researches of former chemists on the subject, 

 he commenced with the same disadvantages which had baffled the skill 

 and perseverance of Sir Humphry Davy. The plan he at first proposed 

 was, to receive a well-defined shadow upon a sheet of paper covered with 

 a solution of nitrate of silver, by which means the part shaded would re- 

 main white, while the surrounding portion was blackened by exposure to 

 the light. But he was well aware that the sketch thus obtained would re- 

 quire to be protected from the rays of the sun, and examined only by an 

 artificial light. He had carried these inquiries to some exteut, and be- 

 come possessed of several curious results before he learned the steps which 

 others had taken to attain the same object : and the decided terras in 

 which Sir Humphry Davy expresses his failure might perhaps have dis- 

 couraged his less experienced follower, had he not fortunately already 

 conquered the difficulty which had destroyed the hopes of the former 

 chemists. 



Mr. Talbot continues : — " In the course of my experiments directed to 

 that end, I have been astonished at the variety of effects which I have 

 found produced by a very limited number of different processes w^hen com- 

 bined in various ways; and also at the length of lime which sometimes 

 elapses before the full effect of these manifests itself with certainty. For 

 I have found that images formed in this manner, which have appeared in 

 good preservation at the end of the twelve months from their formation, 

 have nevertheless somewhat altered during the second year." He was 

 induced from this circumstance to watch more closely the progress of this 

 change, fearing that in process of time all his pictures might be found to 

 deteriorate; this, however, was not the case, and several have withstood 

 the action of the light for more than five years. 



The images obtained by this process are themselves white, but the 

 ground is differently and agreeably colored ; and by slighdy varying the 

 proportions, and some trifling details of manipulation, any of the following 

 colors were readily obtained : — light blue, yellow, pink, brown, black, and 

 a dark green nearly approaching to black. 



The first objects to which this process was applied were leaves and 

 flowers, which it rendered with extraordinary fidelity, representing even 

 the veins and minute hairs with which they were covered, and which 

 were frequently imperceptible without the aid of a microscope. Mr. Tal- 

 bot goes on to mention that the following considerations led hira to con- 



possi 



Nitrate of sil- 



ver, which has become darkened by exposure to the light, is no longer the 

 same chemical substance as before ; therefore, if chemical re-agents be 

 applied to a picture obtained in the manner already mentioned, the dark- 



