204 ANNUAL OF SCIENTIFIC DISCOVERY. 



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the glass enters into fusion, the image sinks into the interior of the glass 

 without being altered, and covers itself with a vitreous varnish. It appears 

 like a design of great delicacy, enclosed between two plates of glass ; and, 

 if positive proofs are employed, the method may be used for making 

 pictured glass which may, without doubt, be colored by the ordinary pro- 

 cesses. Sllliman's Journal. 



HELIOGRAPIIIC ENGRAVING. 



The following process, invented by M. Baldees, appears to bring to per- 

 fection the mode of engraving by the sun. The results obtained are very 

 beautiful ; and although the author has not described to us fully all the 

 details, we know enough to give a general idea of his method. 



On a plate of copper covered with petroleum, a photographic proof on 

 paper of the object to be engraved is placed. This proof is a positive, and 

 w r ill necessarily make a negative on the metal by the action of the light. 

 After an exposure of a quarter of an hour to the sun, the image is 

 reproduced on the resinous coating, but it is not yet visible. It is made to 

 appear by washing the plate with a solvent, which removes the parts not 

 impressed by the light, and brings out a negative picture made by the 

 resinous tracings of the bitumen. The designs are very delicate. The tra- 

 cings receive solidity by an exposure during ten days to the action of a 

 diffused light. When thus hardened, the plate of metal is plunged into a 

 bath of sulphate of copper, and is then connected with the pole of the 

 battery. If with the negative pole, a layer of copper in relief is deposited 

 011 the parts of the metal not protected by the resinous coating. If with 

 the positive pole, the metal is graved out in the same parts, and thus an 

 etched engraving is obtained. Paris Correspondence Sittiman's Journal. 



NATURE DOING HER OWN ENGRAVING. 



In the fifth volume of the Denkshrifteii of the P.oyal Academy of 

 Sciences, at Vienna, there is a paper by M. Aver, and numerous plates 

 illustrating a new style of engraving. The plates represent leaves, plants 

 from an herbarium, lace and other objects, and in each case the object 

 appears to be on the paper, the surface being raised and the coloring per- 

 fect. The deception is so complete that without a magnifying glass it is 

 almost impossible, in one or two instances, to be sure that the object itself 

 is not there. The process employed is the following : The pressed plant, 

 or other object, is placed between a plate of copper and one of lead, and 

 subjected to pressure. The original thus produces a strong impression on 

 the lead plate. By inserting the requisite colors with a point in the 

 depressions, a figure colored to nature, with different colors in its different 

 parts, may be obtained at a single printing. From the lead plates copies 

 may be taken by stereotype or galvanism, and copper plates are thus 

 obtained more durable than those of lead. Gutta-percha may be used in 



