266 ON DRAWINGS OF FLOWERS, &C. 



and Wollaston, in testing the chemical action of the rays of the 

 sblar spectrum ; still, in this country it was not, I believe, applied 

 to any purpose likely to be of use to the naturalist and traveller, 

 until brought into notice by the researches of Mr. Talbot. It is 

 not a little amusing to observe how many pretenders to the dis- 

 covery have started up since the announcement of Mr. Talbot's 

 discovery, and that of M. Daguerre in France. The latter gen- 

 tleman has, through M. Arago, at a late meeting of the French 

 Institute, announced his mode of preparing a sensitive paper, far 

 exceeding that of Mr. Talbot in delicacy, but otherwise possess- 

 ing the same property of indicating intensity of light by depth of 

 colour, and consequently differing from that marvellous prepara- 

 tion which he is said to possess, and which represents shadows 

 by depth of colour, precisely as in nature. 



M. Daguerre prepares his heliographic paper by immersing a 

 sheet of thin paper in hydrochloric ether, which has been kept 

 sufficiently long to be acid ; the paper is then carefully and com- 

 pletely dried, as this is stated to be essential to its proper prepa- 

 ration. The paper is next dipped into a solution of nitrate of silver 

 (the degree of concentration of which is not mentioned,) and dried 

 without artificial heat in a room from which every ray of light is 

 carefully excluded. By this process, it acquires a very remark- 

 able facility in being blackened on a very slight exposure to light 

 even when the latter is by no means intense ; indeed by the dif- 

 fused day-light of early evening in the month of February. This 

 prepared paper rapidly loses its extreme sensitiveness to light, and 

 finally becomes not more readily acted upon by the solar beams 

 than paper dipped in nitrate of silver only. M. Daguerre renders 

 his drawings permanent by dipping them in water, so as to dissolve 

 all the undecomposed salt of silver. 



This process is very inconvenient, for many reasons, among 

 which are the difficulty of procuring, as well as the expense of 

 hydrochloric ether ; on this account I prefer Mr. Talbot's process, 

 although it is to be regretted that this gentleman has not stated 

 more explicitly the proportions in which he uses the ingredients 

 employed in the preparation of his sensitive paper. I have per- 

 formed a set of experiments on this subject, and can recommend 

 the following proportions as the most effective and economical. 

 Two hundred grains of common salt are to be dissolved in a pint 

 of water, and sheets of thin blue wove post paper saturated with 

 the solution, which, for this purpose, should be poured into a dish. 



