60 J. Waterhousc — The Appllcntlon of Tliotograpliij [No. 2, 



being absolute facsimiles of the original maps submitted by the surveyors, 

 they are entirely, free from the errors that even the most careful draughts- 

 man is liable to make when copying by hand, and they faithfully preserve 

 the appearance and character of the ground exactly as delineated by the 

 surveyor. 



In most foreign topographical establishments, I believe, the principal 

 use of photography is for making reductions, and not so much for the repro- 

 duction of maps on the same scale as the originals. In India, however, 

 photozincography is very largely used for full-scale reproductions. Thus, 

 the whole of the standard maps of the Topographical Surveys on the scale of 

 1-inch to the mile and the Cadastral village maps of the Revenue Survey, 

 on the scales of 32 inches to the mile, for Bengal, and 16 inches to the mile, 

 for the N.-W. Provinces, are reproduced on the same scale and are 

 not reduced for publication on any smaller scale. In some cases, however, 

 the surveys are made and drawn on the scale of two inches to a mile and 

 are then reduced to one-inch, with a great improvement in the general 

 appearance of the finished maps — reductions always appearing sharper and 

 more highly finished than reproductions to scale. Some of the maps of the 

 Revenue Surveys are reduced to the standard scale of 1-inch to the mile 

 by a double reduction from the maps on the original scale of survey — 4 

 inches to the mile. These are first photozincographed, in sections of con- 

 venient size, on the reduced scale of 2 inches to the mile and some prints are 

 struck off in blue ink. Upon these blue prints, the draughtsman re-draws 

 the map in a stjle suitable for a further reduction to one-half, leaving 

 out all details not required on the 1-inch map and generalising the hill 

 features, &c., so as to produce a proper effect when reduced. By the use 

 of these blue prints, the labour of making a piecemeal reduction with the 

 pantograph is saved, and the draughtsman can produce a more accurate 

 result. 



Silver print reductions to one-fourth of the standard 1-inch maps are 

 made for the use of the engravers in preparing the sheets of the Atlas of 

 India on the quarter-inch scale. 



In the Photozincographic Ofiices at Puna and Madras more use appears 

 to be made of reduction for the village maps than in the Calcutta Ofiice. 



The photographic processes applicable to the reproduction of maps 

 are : 



I. — Photographic printing on Sensitive Papers. In these methods 

 prints are obtained on a sensitive surface of paper prepared with the salts 

 of silver, platinum and iron, or with certain salts of chromium in conjunc- 

 tion with pigmented gelatine. In all of them the whole of the photogra- 

 phic operations connected with the printing have to be repeated for every 

 impression. 



