1878.] to the Beproduction of Maps and Flans. 61 



II. — PJioto-lithograplty or Plioto-zincography , or the methods by which 

 photographic image in greasy ink may be produced on, or transferred to, a 

 lithogra2)hic stone or zinc plate and printed off in the lithographic press. 

 The photographic operations cease with the production of the image in 

 greasy ink, and the impressions are produced by the ordinary operations of 

 lithographic printing. The use of these processes is, however, limited to the 

 reproduction of subjects in line or dot, as they can only reproduce half 

 tones in a very imperfect manner, 



III. — Fhoto-collotype^ or the method of producing a photographic image 

 on a layer of gelatine applied on a suitable support, so that when the 

 gelatine surface is moistened, impressions may be obtained from it in 

 printing ink. By this method, also, a photographic image once produced 

 on the printing surface of gelatine is capable of yielding some hundreds of 

 impressions in the printing press ; and instead of the subjects for reproduc- 

 tion being confined to those in dot or line, as in photo-zincography, any 

 subject can be copied which is capable of giving a good photograph by 

 the ordinary process of silver printing. 



IV. — Woo dhury -type, or the method whereby a photographic image is 

 impressed into a soft metal plate, somewhat in the same manner as in the 

 operation of nature-printing, formings a mould into which liquid coloured 

 gelatine is poured and attached under pressure to a sheet of paper, thus 

 yielding an image in which the lights and shades of the picture are formed 

 by different thicknesses of coloured gelatine. 



V. — Heliography or Fhoto-engraving^ the method of obtaining on 

 a metal plate a photographic image in intaglio capable of giving impressions 

 in the copper-plate press In this method the engraved plate once obtained 

 serves for the impression of a large number of copies and may be inde- 

 finitely multiplied by electrotyping. 



VI. — Fhoio-typography, or the method of obtaining by means of pho- 

 tography an image in relief on a metal plate, which may be mounted on a 

 block to be set up with type and be printed in the ordinary printing press. 

 These blocks may also be indefinitely multiplied by electrotyping in the same 

 manner as ordinary woodcuts. 



It will be observed that the five last-named processes all possess the 

 great advantage that, once the photograpliic image has been obtained on the 

 printing surface, the operations of printing can be accomplished by the 

 same means and at the same rate as by the ordinary industrial melhods. 

 The printing may be performed by night or by day, quite independently of 

 the agency of light, and requires no further chemical manipulations. 



It would be beyond the scope of this pa[)er to enter fully into the 

 practical details of these various processes of [)hotographic printing, as 

 my object is merely to review those applicable to cartographic pur- 

 9 



