204: THE CALOTYPE. SECT. XXIV. 



Davy, took up the subject : they produced profiles and tracings 

 of objects on surfaces prepared with nitrate and chloride of silver, 

 but they did not succeed in rendering their pictures permanent. 

 This difficulty was overcome in 1814 by M. Niepce, who pro- 

 duced a permanent picture of surrounding objects by placing 

 in the focus of a camera-obscura a metallic plate covered with 

 a film of asphalt dissolved in oil of lavender. 



Mr. Fox Talbot, without any knowledge of M. Niepce's ex- 

 periments, had been engaged in the same pursuit, and must be 

 regarded as an independent inventor of photography, one of the 

 most beautiful arts of modem times : he was the first who suc- 

 ceeded in using paper chemically prepared for receiving impres- 

 sions from natural objects ; and he also discovered a method of 

 fixing permanently the impressions that is, of rendering the 

 paper insensible to any further action of light. In the calotype, 

 one of Mr. Talbot's applications of the art, the photographic 

 surface is prepared by washing smooth writing-paper, 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, build- 

 ings, 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 micro- 

 scope reveals new beauties. 



Since the effect of the chemical agency of light is Jto destroy 

 the affinity between the salt and the silver, Mr. Talbot found 

 that, in order to render these impressions permanent on paper, 

 it was only necessary to wash it with salt and water, or with 

 a solution of iodide of potassium. For 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 calotype 

 picture is negative, that is, the lights and shadows are the reverse 

 of what they are in nature, and the 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 



