187S.] to the Reproduction of Mnpii and Plans. 121 



The applications of photography to copying purposes may be divided 

 into two principal classes, according as the original subjects have or have 

 not been specially prepared for photographic reproduction. 



As regards subjects in the first class, it is possible to adapt and 

 prepare the original drawings, so as to fit them for the requirements of any 

 photographic process considered most suitable to meet the object in view. 

 As a rule such drawings will be intended for publication or reproduction in 

 large numbers by the photo-mechanical processes rather than by silver or 

 pigment-printing, which will do very well for small numbers. 



For the reproduction of maps and plans a process is required which 

 will admit of large-sized sheets being produced. Many processes capable 

 of yielding very beautiful results when employed for subjects of small size 

 are quite un suited for larger work. 



For map- work in line, photozincography will generally be found most 

 suitable and convenient on account of the simplicity of the operations, the 

 facilities it gives for joining several small sections into large sheets, and 

 the short time required for turning out a large number of copies. Under 

 favourable conditions, photozincography will give very excellent results for 

 all practical purposes. If anything finer is required for permanent or 

 standard purposes, then one of the engraving processes would be most suit- 

 able, and in certain cases the photocoUotype could also be applied with 

 advantage. For diagrams and small maps &c., to be printed with type, 

 photo-typography will prove useful. 



For shaded or coloured maps and drawings, photozincography and photo- 

 typography are not applicable, and recourse must be had either to photo- 

 collotype or to one of the engraving methods with bichromate and gelatine 

 which will give gradation of shade, such as Rousselon's, Woodbury's or 

 Geymet's. It is probable that these latter processes will prove of great use 

 as soon as their requirements and capabilities are better known. 



It may be as well to repeat that whenever it is possible, drawings 

 specially prepared for reproduction by photography should be drawn on 

 a. larger scale than they are ultimately required. 



With regard to subjects in the second class, it is evident that the choice 

 of a photographic process must depend very much on the nature of the 

 original subject and its suitability for photographic reproduction by any 

 particular method, as well as on the number of coj^ies required. 



It would be impossible to notice here all the cases coming within this 

 class, it will therefore perhaps be sufficient to state that in most instances 

 when only a few copies are required and permanency is not an object, 

 ordinary silver printing will be found most convenient for all classes of 

 subjects ; and where the original is sufficiently translucent and photographic 

 cameras not available, both negative and copy may be obtained in this 

 manner sufficiently good for many practical purposes. 



