NATURAL PHILOSOPHY. 189 



which cannot fail to produce very important results in portrait paint- 

 ing. It is purely mechanical, and consists in so placing the daguerre- 

 otype as to throw an exact copy of it, magnified to any required size, 

 upon canvass placed at the distance of a few feet from it. In this 

 way a most accurate likeness, the size of life is projected upon can- 

 vass from a daguerreotype ; and may be sketched with a crayon or 

 otherwise, to be finished and colored with oils afterwards. The utility 

 of the invention consists in enabling the artist to get a perfect copy 

 of the features with infinitely more accuracy and ease than in the or- 

 dinary way ; while it does not interfere in the least with the subse- 

 quent finish of the portrait. 



A new method of portrait painting has also been recently introduced 

 in Paris, by Horace Vernet. He mixes his colors with olive oil, which 

 avoids the* drying of the colors, and the cleansing of the brushes. 

 When the painting is finished, a layer of absorbing earth is applied to 

 the back of the canvass ; the oil is absorded and the painting becomes 

 a pastel or crayon drawing. The earth is then removed, and a coat 

 of flaxseed oil is substituted ; this penetrates the colors, and the work 

 is done. 



ENGRAVING FROM DAGUERREOTYPES. 



Various attempts have been made to transform, by chemical agents, 

 the plate of the daguerreotype into an engraved plate, engraved by 

 the image formed by light, from which the operator might strike off, 

 by the ordinary process of impression, a certain number of proofs on 

 paper. Dr. Donne made the first experiments in this direction ; MM. 

 Grove, Berres, Choiselat, Fizeau, followed, with different success, his 

 lead. Attempts have also been made to transfer upon stone photo- 

 graphic drawings, and M. Lemercier has produced several lithographs 

 obtained by this way. Doubtless researches would have been pushed 

 further in this direction, had not a formidable rival entered the list : 

 photography upon paper, which allows the operator to obtain, by means 

 of an original plate (cliche,) a large number of identical proofs, con- 

 sequently most persons have judged they would herein discover the 

 practical' solution of the multiplied publication of the products of pho- 

 tography. Hence, all efforts have tended towards completing Mr. 

 Talbot's invention, by endowing the plates (cliches) with a greater 

 durability, accelerating and regulating the transfer to paper, with, at 

 the same time, a complete preservation of the details of the original. 



It may appear ratber strange, that it is Mr. Talbot himself who re- 

 verts to engraving proper, and furnishes new processes, which one day 

 may, perhaps, limit the employment of calotype paper. Mr. Talbot 

 discards silver and copper, as the plate on which he proposes to em- 

 ploy chemical reactives. It has been ascertained these two metals are 

 too soft to resist the wear and tear which necessarily accompanies a 

 large impression, and to preserve unaltered all the finer details of an 

 operation whose principal merit is to reproduce all the details of a 

 luminous image. Mr. Talbot sought to engrave upon steel, and he 



