NATURAL PHILOSOPHY. 143 



will modify the color of those substances in absorbing it. The experiment 

 may be varied as follows : Let a fern leaf be laid upon a piece of prepared 

 silk and kept flat upon it by a pane of glass ; then that part of the silk which 

 is protected by the leaf will retain its original color, while all the rest will 

 receive the impression of light, as above described, forming the ground on 

 which the figure of the leaf will appear in white, gray, or whatever other 

 color the silk may have had before the operation. The richest patterns may 

 thus be obtained on plain silks, and at a comparatively small expense. 



Photographic Enamels. MM. Armengaud, in the Genie Industrie!, an- 

 nounce that "the MM. Bruder, of Neufchatel (Switzerland), have discovered 

 a process by which photographs may be developed on white enamel, incor- 

 porated by vitrification, and covered with a glaze of glass also melted and 

 incorporated with the enamel. They apply the same process also upon 

 metals and wood." 



Practical Applications of Photography. During the Paris exhibition of 

 1855, some of the non-commissioned officers of the Royal Engineers who 

 were employed there received instruction in photography, and on their 

 return to England their knowledge thus obtained was turned to a practical 

 use by Colonel James, the director of the Ordnance Survey, in making 

 reductions of the various maps and plans required in that Avork. This is the 

 first instance of the scientific use of photography on a large scale, and some 

 idea may be formed of its importance from the fact that the saving in this 

 item only has been not less than 20,000. 



Since then, a systematic course of instruction in photography has been 

 given to non-commissioned officers in the English engineer corps, and 

 this constant supply of men practiced in the art is maintained. These are 

 distributed in all parts of the world, where a detachment of engineers is 

 maintained, and the orders to officers commanding companies to which pho- 

 tographers are attached, are, to send home, periodically, photographs of all 

 works in progress, and to photograph and transmit to the war department 

 drawings of all objects, either valuable in a professional point of view, or 

 interesting as illustrative of history, ethnology, natural history, antiquities, 

 etc., etc. 



New Photographic process for the Printing of Positive Proofs. A piece of 

 sulphur is dissolved in sulphuret of carbon, in the proportions of twenty-five 

 paits of the former to seventy-five of the latter, and the solution is then fil- 

 tered. The solution in sufficient quantity is poured on the paper, which is 

 shaken quickly in every direction, in order that it may spread equally, and 

 crystals of opaque sulphur may not form. The paper thus prepared is kept 

 in the dark. At the required moment, the paper is put under an ordinary 

 negative, and exposed to the light for twenty -five seconds to a minute, or 

 five minutes on a dark day. When taken out, nothing is seen on the paper. 



Nothing appears upon the surface of the paper when it is removed from 

 the slide. It is then put over a mercury bath, at the bottom of which are 

 placed some grams of this metal. The sulphurized paper from the camera 

 is then exposed at the distance of eight centimetres above the mercury 

 (which is heated meantime), sustained on a frame of paper forming a cover 

 to the bath, on the under side of which, with its face to the mercury, is the 

 prepared paper. The vapor of mercury combines with the portions of sul- 

 phur which have received the influence of the sun's rays, forming a yellow- 

 ish brown sulphuret of mercury, which perfectly reproduces the details of 



