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the publication could keep pace with the surveys, and the consequence was that the record rooms became filled with valuable materials that often could not be turned to practical account till they had become antiquated and out of date. Now, on the contrary, by the aid of photozincography, the publishing branches are able to keep pace with the progress of the Surveys so closely that as a rule each season's mapping of all the 1-inch Topographical and some of the Revenue Surveys is reproduced and published before the drawing of the following season's maps is taken in hand. An immense amount of work is thus done that could never have been undertaken by lithography and engraving alone, even though the transfer of the engraving of the Atlas of India to Calcutta has greatly facilitated the early publication of the latest additions to the Atlas year by year. And not only are the ordinary departmental publications thus hastened, but a very large number of miscellaneous maps and drawings are reproduced specially for the use of other departments of the public service.
The following table of the work executed by the Photographic Branch of the Surveyor General's Office, Calcutta, during the year 1877, will give an idea of the very large extent to which photography is being used for the reproduction and publication of the results of the Imperial Surveys and other miscellaneous demands.
Grand Total, ..
* 20,962:00 square feet.
+ 22,027.40 square feet.
In the Great Trigonometrical Survey Office at Dehra Dún, during the year 1876-77, 117 maps and 30 charts, besides miscellaneous diagrams were photographed, and 25,529 copies printed from them; 297 blue prints and silver prints were also made.
At the Govt. Photozincographic Office, Púna, during the same year, the number of negatives taken was 2,745, the number of maps photozincographed was 1,798, and the number of copies printed off (including copies of 79 lithographs) was 74,739. Since the formation of the office, in 1867, to the present time 9,100 maps have been photozincographed.
The specific advantages to be gained by the use of photography for the reproduction of maps and plans are :
1. Rapidity of production and multiplication, especially when employed for copying subjects containing close and intricate details. The gain varies according to the amount of detail and the time that would be taken by a skilled draughtsman or engraver to make the copy by hand. For instance, a highly finished map that would take several months to lithograph or engrave, may by the aid of photography be copied and some hundreds of copies printed off within a week.
2. The perfect fidelity with which the most delicately minute and intricate details are copied. The most skilful and careful draughtsman is liable to make errors in copying, and never can attain the same accuracy of delineation, especially of minute objects, as is obtained with the
3. The facility with which copies may be obtained on scales larger or smaller than the original. The extent to which this may be taken advantage of depends very much upon the object in view as well as upon the style of the original, and the relative thickness and size of the lines and details composing it; but notwithstanding certain drawbacks and inconveniences it may sometimes be attended with, this facility of enlarging or reducing the scale of an original drawing with the most perfect accuracy and with the absence of all personal crror, is one of the most important advantages of photography, and its immense superiority in this respect over the pentagraph and other methods has been proved to be beyond question.
4. The comparative cheapness of the photographic methods. The relative cost of hand labour and photography is affected by several considerations, e. g., the nature of the subject, the process employed, the number of copies made and the pay of the photographers as compared with that of draughtsmen. In most cases it will be found that when it is really an advantage to employ photography in reproducing maps for any particular purpose, the cost will be far less than it would be by employing hand labour.
Notwithstanding these advantages, the use of photography as a means of reproducing maps and plans for publication has not extended so much as might have been expected, partly on account of defects inherent in photographic copying, and only to be overcome by great skill and long experience on the part of the photographer, and partly owing to the difficulty of making draughtsmen fully understand the requirements to be fulfilled when preparing maps to be reproduced by photography for publication, in order to produce satisfactory results, and that they must strictly refrain from using colour and draw the map neatly in black and white, so that every line may be reproduced of its proper strength, according as the map is to be copied on the same scale as the original or to be reduced.
It matters little how roughly drawn or highly coloured an original drawing or map may be, if it is intended to lithograph or engrave it, because a skilled lithographer or engraver can easily put it into proper and conventional form ; but when such a drawing is handed to the photographer he can only produce a facsimile of it with all its deficiencies—the coloured details hidden under a black mass of shade, the finer parts perhaps wanting altogether, the writing rough and broken, or so small as to be almost invisible, besides other defects caused by the unsuitableness of the drawing for reproduction by photography, and these defects are liable to be unduly attributed to the process.
These difficulties were felt in all their force when it was first determined to introduce photozincography for the publication of the maps of the Imperial Indian Surveys, because till that time these maps had been drawn in a very delicate, highly finished style, with many of the details on them coloured and the hill features shown by brush shading. It was soon seen that an entire change of style was necessary and that the original maps prepared specially for photographic reproduction, must be drawn in pen and ink lines alone, without colour or brush-shading. It was some time before the desired results were obtained, but after several years' experience a high degree of excellence has been attained in the
preparation of original maps suitable for photographic reproduction, and now all maps of the above Surveys and most of the miscellaneous maps and drawings received from other departments are drawn with this object.
The change of style has been regretted by some as spoiling the beauty and finish of the maps, and the want of colour certainly has some drawbacks, but there can be no doubt that the necessity for drawing the original maps so that they may be fit for immediate publication has effected here, as it has also been found to do wherever photozincography or photolithography has been introduced, an in mense improvement in the style of drawing of the manuscript maps as well as in the accurate delineation of the ground. The photozincographed copies as a rule appear somewhat coarse and rough when compared with good lithographs or engravings, but they possess the great advantage of being produced quickly and cheaply; while being absolute facsimiles of the original maps submitted by the surveyors, they are entirely free from the errors that even the most careful draughtsman 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 reproduction 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 convenient 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 style 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 Offices at Púna and Madras more use appears to be made of reduction for the village maps than in the Calcutta Office.
The photographic processes applicable to the reproduction of maps
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 conjunction with pigmented gelatine. In all of them the whole of the photographic operations connected with the printing have to be repeated for every impression.
II.-Photo-lithography or Photo-zincography, or the methods by which photographic image in greasy ink may be produced on, or transferred to, a lithographic 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.--Photo-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 reproduction 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.-Woodbury-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, forming 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 Photo-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 indefinitely multiplied by electrotyping.
VI.--Photo-typography, or the method of obtaining by means of photography 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 photographic image has been obtained on the printing surface, the operations of printing can be accomplished by the same ineans and at the same rate as by the ordinary industrial methods. 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 paper to enter fully into the practical details of these various processes of photographic printing, as my object is merely to review those applicable to cartographic pur