294 THE HISTORY OF SOME DISCOVERIES OF PHOTOGRAPHY. 



Niepce communicated to Daguerre the particulars of the process 

 employed by him, which has been already described (Chap. II) urder 

 the term " heliography."' Niepce died in July, 1833, but he has left 

 some letters which clearly show that he had been a most industrious 

 investigator. One extract appears of particular importance. " T re- 

 peat it, sir," he says, " I do not see that we can hope to derive any 

 advantage from this process (the use of iodine) more than from any 

 other method Avhich depends upon the use of metallic oxides," etc. 

 Again, he says, "a decoction of Thlaspi (Shephercrs purse), fumes 

 of phosphorus, and particularly of sulphur, as acting on silver in the 

 same way as iodine, and caloric, produce the same effects by oxidizing 

 the metal, for from this cause proceeded in all these instances their 

 extreme sensibilitly to light. After the death of M. Nicephore .Niepce 

 a new agreement was entered into between his son, M. Isidore Niepce, 

 and Daguerre that they should pursue their investigations, in common 

 and share the profits, whatever they might eventually prove to be. 



The discovery of Daguerre was reported to the world early in Jan- 

 uary, 1839, but the process by which his beautiful pictures were pro- 

 duced was not made known until the July following, after a bill was 

 passed securing to himself a pension for life of 6,000 francs, and to 

 M. Isidore Niepce, the son of Monsieur Niepce above mentioned, a 

 pension for life of 4,000 francs, Avith one-half in reversion to their 

 widows. It was regretted that after the French Government had 

 thus liberally purchased the secret of the process of the daguerreo- 

 type for " the glory of endowing the world of science and art Avith 

 one of the most surprising discoveries that honor their native land," 

 on the argument that " the invention did not admit of being secured 

 by patent, for as soon as published all might avail themselves of its 

 advantages," that its author should have guarded it by a patent right 

 in England. 



From the primary importance of this very beautiful branch of the 

 photographic art I shall devote some space to a description of the 

 original process, reserving for the division devoted to the manipula- 

 tory details the description of each improvement which has been pub- 

 lished having any practical advantage, either by lessening the labor 

 required or reducing the expense. 



The pictures of the daguerreotype are executed upon thin sheets 

 of silver plated on copper. Although the copper serves principally 

 to support the silver foil, the combination of the two metals appears 

 to tend to the perfection of the effect. It is essential that the silver 

 should be very pure. The thickness of the copper should be sufficient 

 to nuiintain perfect flatness and a smooth surface, so that the images 

 may not be distorted by any warping or unevenness. Unnecessary 

 thickness is to be avoided on account of the weight. 



The process is divided by Daguerre into five operations. The first 



