SCT. XXIV. M. DAGUERRE 195 



ing smooth writing-ffoper, first with a solution of nitrate 

 of silver, then with bromide of potassium, and again with 

 nitrate of silver, drying it at a fire after each washing ; 

 the paper is thus rendered so sensitive to light that even 

 the passage of a thin cloud is perceptible on it, conse- 

 quently it must be prepared by candle-light. Portraits, 

 buildings, insects, leaves of plants, in short every object 

 is accurately delineated in a few seconds, and in the 

 focus of a camera obscura the most minute objects are 

 so exactly depicted that the microscope reveals new 

 beauties. 



Since the effect of the chemical agency of light is to 

 destroy the affinity between the salt and the silver, Mr. 

 Talbot found that in order to render these impressions 

 permanent^pn paper, it was only necessary to wash it 

 with saJBB water, or with a solution of iodide of po- 

 tassiunaf^Wr these liquids the liquid hyposulphites 

 have been* advantageously substituted, which are the 

 most efficacious in dissolving and removing the unchanged 

 salt, leaving the reduced silver on the paper. The cal- 

 otype picture is negative, that is, the lights and shadows 

 are the reverse of what they are in nature, and {& 

 right-hand side in nature is the left in the picture ; but 

 if it be placed with its face pressed against photographic 

 paper, between a board and a plate of glass, and exposed 

 to the sun a short time, a positive and direct picture as 

 it is in nature is formed ; engravings may be exactly 

 copied by this simple process, and a direct picture may 

 be produced at once by using photographic paper already 

 made brown by exposure to light. 



While Mr. Fox Talbot was engaged in these very 

 elegant discoveries in England, M. Daguerre had brought 

 to perfection and made public that admirable process by 

 which he has compelled Nature permanently to en- 

 grave her own works ; and thus the talents of France 

 and England have been combined in bringing to perfec- 

 tion this useful art. Copper, plated with silver, is suc- 

 cessfully employed by M. Daguerre for copying nature 

 by the agency of light. The surface of the plate is 

 converted into an iodide of silver, by placing it horizon- 

 tally with its face downward in a covered box, in the 

 bottom of which there is a, small quantity of iodine 



