NATURAL PHILOSOPHY. 121 



NOVELTIES IN PHOTOGRAPHY. 



Permanency of Photographs. The Paris correspondent of The 

 Photographic News (London) states that, at a late meeting of the Paris 

 Photographic Society, M. Davanne presented two photographic pic- 

 tures, on paper, which had been submitted to the test of exposure in two 

 exhibitions (18G1 and 1862), and which showed no signs of fading or 

 alteration whatever. This, then, may be accepted as a satisfactory 

 proof that photographs, when carefully prepared, are permanent ; for 

 the pictures in question were submitted to the severest test to which 

 photographs are ever likely to be exposed, the conditions being every 

 variation of light, heat, moisture, etc., and they remain as fresh and pure 

 as at first. It was also remarked that photographs are more liable to 

 change when kept in a portfolio than under glass exposed to luminous 

 action. A sulphurized proof, if kept in a perfectly dry place, remains 

 for a very long time without exhibiting any signs of alteration, while 

 in a damp place, change is immediately evident. Thus, a photograph 

 carefully framed is much better sheltered from humidity than when 

 kept in a portfolio. 



Photographic Engraving. The London Athenceum, under date of 

 November 14th, 1863, states that it has recently seen a beautiful speci- 

 men of photoglyphic engraving on steel, in other words, a photo- 

 graphic picture on steel, --effected solely by the agency of light acting 

 on certain chemicals. The specimen (it is stated by Mr. Fox Talbot) 

 is quite untouched. It represents an exquisite scene in Java, - - a ra- 

 vine and rivulet fringed with banana-trees. Not the least wonderful 

 circumstance connected with it is, that at least 5,000 copies can be 

 taken before the plate deteriorates. Such a result, after so many years 

 of labor, must be, for Mr. Fox Talbot, a genuine triumph. 



New Photographic Fixing Agent. To fix photographic pictures, a 

 solution of the hyposulphite of soda has been the common agent em- 

 ployed. In this, the picture is treated, and is thus prevented from 

 changing. The London Photographic News asserts that the days of 

 this agent in photography are numbered, and that sulphocyanide of 

 ammonium will take its place as a superior agent, by the use of which 

 a faded positive picture will be unknown. The original source of the 

 cyanide of ammonium is the thick, tarry liquid remaining after the 

 separation of the free ammonia from gas liquor : this has long been 

 known to contain large quantities of sulphocyanide of ammonium, but 

 hitherto all attempts to separate it from the impurities which accom- 

 pany it have failed. 



Photo-Lithography. A communication has been recently made to 

 the French Academy, by M. Morvan, in which he describes a new 

 method for obtaining photographic impressions upon stone, and which 

 he can afterward print off. He first applies a coating, in the dark, of a 

 varnish composed of albumen and bichromate of ammonia. Upon this he 

 lays the right side of the image to be reproduced, whether it be on glass, 

 canvas, or paper, provided it be somewhat transparent. This done, he 

 exposes the whole to the action of light for a space of time, varying be- 

 tween thirty seconds and three minutes, if in the sun, and between ten 

 and twenty-live minutes, if in the shade. lie then takes off the original 



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