NATURAL PHILOSOPHY. 133 



" These operations may appear long in the description, but they are 

 rapidly enough executed after a little practice." 



To the images obtained by this new process, Mr. Talbot has applied 

 the term amphi types, because they appear either positive or negative, 

 according to the circumstances of 'light under which they are viewed. 

 Thus, if held against a bright light, or against a sheet of white paper, 

 they appear negative, and the reverse when held against a black sur- 

 face and seen in oblique reflected light. 



New Process for copying from Engravings. A new process for 

 copying engravings has been discovered by M. Niepce, of France. It 

 consists in submitting the engraving to the vapor of iodine (at a tem- 

 perature of 15 or 20 C.) for about two minutes ; a longer time is 

 necessary, if the temperature be less elevated ; ten grammes of iodine 

 to be used per square of four inches. The paper intended to receive 

 the impression is to be covered with a coat of paste, taking care pre- 

 viously to have it moistened with water containing one part of pure 

 sulphuric acid. The proofs, after being pressed with a linen cloth, 

 present a design of admirable purity. Those impressions taken on 

 paste will, however, in drying, become vaporous ; but, if taken on 

 paper, prepared with one or two layers of starch, the design will not 

 only be clear, but will preserve much better. What is most extraor- 

 dinary is that many impressions may be taken from the same print 

 without submitting it to a new preparation, the last proofs being 

 always the clearest. Designs of various colors may thus be obtained, 

 according as the paste is more or less boiled, or according to the quan- 

 tity of acid used. Proofs may also be taken on different metals, by 

 observing the following precautions. In submitting the engraving to 

 the vapor of iodine, care should be taken to have it perfectly dry, in 

 order that the white portions of it may become impregnated. In this 

 case it should be exposed but a few minutes to the vapor. Let it be 

 afterwards applied, without wetting it, to a plate of silver, and then 

 placed under a press ; at the end of five or six minutes there will be a 

 most faithful reproduction of the original. By afterwards exposing the 

 plate to the vapor of mercury, a proof similar to that of a daguerreo- 

 type is obtained. 



MM. CLEXISSOX and TERREIL have presented to the French Academy 

 a method of obtaining daguerreotype impressions on metallic surfaces, free 

 from the usual mirror-like appearances, which destroy, to a considerable 

 extent, the artistical effect. The process consists in submitting the 

 impression, after washing in the hypo-sulphate of soda solution, to the 

 action of very weak aqua regia, which transforms the amalgam, pro- 

 ducing the white parts of the impression, into chlorides of silver and 

 mercury unalterable to the action of the light, and which produces on 

 the dark parts a chloride of silver, susceptible of alteration under the 

 influence of light. After this operation the harmony of tints is pre- 

 served, and the image fixed, as if by chloride of gold. 



Gutla Percha in Photography. Mr. Fry. of England, has _ greatly 

 improved the process of- obtaining pictures on glass, by the addition of 

 gutta percha to collodion gun-cotton dissolved in ether. This is 

 employed with the ordinary materials for the processes on glass, the 



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