92 J. Waterliouse — The ApplU-atioii of Photography [No. 2, 



graphiques aux eiicres yruaacs,''' and A. Martin's " SandhuGh der Email, 

 photographie und der Phototypie oder des Lichtdruches.'''' 



The great difference between the photocollotype processes and litho- 

 graphy is, that whereas the lithographic stone receives a like quantity of ink 

 in all parts of the image, and is incapable of producing a true and continuous 

 gradation of shade, the moist gelatine film possesses the valuable property, 

 not possessed by the stone, of receiving a greater or less amount of ink in 

 different parts of the image, in exact proportion to the intensity of the 

 action of the light upon them, and is thus capable of reproducing the 

 most delicate gradations of shade as perfectly as they are shown in an 

 ordinary silver print. 



It will thus be readily understood that instead of the advantages of 

 photographic reproduction by cheap and speedy mechanical processes being 

 confined to the reproduction of certain special subjects, they can be extended 

 to all classes of subjects, such as photographs from nature, brush-shaded 

 and coloured maps, MS. records, drawings and paintings of all kinds. Even 

 for line subjects, the process surpasses most of the known processes of photo- 

 engraving, photozincography or photolithography in the delicacy, sharpness 

 and clearness with which the finest lines can be reproduced, as well as in 

 perfect accuracy of scale, owing to there being no intermediate process of 

 transfer, with its attendant washings and pressings, and the plate being 

 printed by vertical pressure. 



The process has the further advantage that the prints do not require 

 mounting, and this makes it very suitable for book illustration, for which, 

 indeed, it is now being very largely used. It is especially valuable for 

 illustrations of a scientific character in cases where otherwise only the 

 highest class of lithography or engraving would be applicable and at an 

 enormously increased expense. 



For the most successful application of the photocollotype processes to 

 the reproduction of maps, the result depends, as in photozincographj'-, very 

 much on the quality of the negative, and that again on the original. 



Any negative that will give a good photographic print will answer, but 

 the successful reproduction of shaded maps or drawings demands consider- 

 able care in the execution of the original drawing as well as in taking the 

 negative. The precautions to be taken in these respects have already been 

 indicated in sections 11 and III. 



For some years past my attention has been given to the utilisation of 

 this valuable process for the reproduction of maps and other photographic 

 work which the Surveyor General's Office is called upon to do for various 

 Government departments. In the Proceedings of the Society for November 

 1871, I described a process which I had found to answer well for line work, 

 and strenuous efforts were made to bring this and other methods into prac- 



