72 J. Wi\i(iY\nmse*—The AjipUcdtlon of FliolorjrfipJiy [No. 2, 



tliey insert the features of the ground, suitably delineated according to the 

 scale. 



A very early application of this process has lately been re-introduced 

 in Germany by HerrKomain Talbot, of Berlin, under the title of the Licht- 

 paus process, with the object of enabling engineers and others to readily 

 prepare a few co})ies of their plans without the necessity of using a camera 

 and other expensive appliances. In this method a print on a sensitive 

 chlorised paper, prepared with nitrate of silver and an organic acid, so that it 

 may be kept for some time in stock ready for use, is first taken by exposing 

 it to light under the original drawing itself, which to secure the best results 

 should be drawn in very black ink on thin paper or vellum cloth. This 

 print, on which the lines are clear and the ground opaque, is simj^ly fixed 

 in a solution of hyposulphite of soda and then thoroughly washed and 

 dried. A second copy is now made from this negative print in exactly the 

 same waj', and as, this time, the lines darken under the clear parts of the 

 negative and the ground remains clear, we obtain a perfect transcript of the 

 original. This process is said to be largely used in Germany for copying 

 maps and engineering plans. It is no doubt useful in many cases where 

 it is undesirable or impossible to make more extensive photographic arrange- 

 ments, but besides being limited to the reproduction of copies on the same 

 scale as the original, it labours under the disadvantages of expense and want 

 of permanency common to all the silver printing processes. 



In the processes just noticed the exposure to light is usually from 15 

 to 30 minutes, but in dull weather, or with certain negatives, it may be 

 much longer ; it is obvious, therefore, that even under the most favourable 

 conditions comparatively few prints can be produced from a single negative 

 in a day. In order to shorten the exposure and permit prints to be pro- 

 duced with much greater rapidity than with the ordinary process, a method 

 has been introduced by Major Libois of the Belgian army, by which, 

 instead of the image being produced at once in its full strength by the 

 action of light, the latter is only allowed to act for a few seconds, and the 

 full effect is produced by treating the print with a developing agent com- 

 posed principally of gallic acid, which at once reduces the silver in the parts 

 acted on by the light, and thus produces a visible image in place of the 

 almost invisible one formed by the action of the light alone. This j^rocess 

 was extensively used in the Depot de la Guerre, Paris, some years ago, and 

 large numbers of maps were turned out by it, I was told, almost as quickly 

 as they could have been printed in the press, and it had the further advan- 

 tage that facsimile copies could be made of maps £j-om which good results 

 could not have been obtained by photolithography. The same process was 

 used at the Depot de la Guerre in Brussels, but not on so large a scale. 

 i hnve also used it with success in India, and it may be recommended i\\ 



