« السابقةمتابعة »
should pass through the Local Governments, but this point may be settled as may be found most expedient in practice.” In accordance with these orders, enquiries have been, and are being made, with a view to ascertain the ports at which it will be desirable to establish tidal stations. The suitability of a port for this purpose will depend, first, on a site being available thereat, on which a self-registering tide-gauge may be erected, so as to be either immediately over the sea, or connected by piping with the sea at some point where there is a depth of not less than 10 to 15 feet of water at the lowest tides; secondly, on the presence of a port officer, who will exercise a general supervision over the operations, and correct the clocks of the several self-registering instruments, whenever necessary, either by direct determinations of time, or by arranging to get the true time from the nearest telegraphic office; thirdly, on the feasibility of making arrangements for the periodical inspection of the instruments at intervals of not less than six months generally, and more frequently when no officer is resident on the spot to superintend the operations. So far as has yet been ascertained, the ports which seem likely to answer all the required conditions are Aden, Kurrachee, Bombay, Carwar, Beypore, Paumben, Madras, Vizagapatam, Akyab, Rangoon, and Port Blair. The following ports are believed to be unsuitable : Surat, Mangalore, Cannanore, Cochin, Muttrun, Negapatam, Coconada, False Point, Diamond Harbour, Moulmein, and Mergui. .* At Aden a self-registering tide-gauge was erected by the local officers about two years ago; but the registers have been taken in such an unsatisfactory manner that the results are not of the slightest use. Captain Baird is now arranging for the establishment of a tidal station there, with proper instruments, and trained men to take charge of them. At Kurrachee a tide-gauge, which was originally set up by Mr. Parkes, has been in work for several years, and has furnished the datá from which tide-tables for the port have been computed annually by Mr. Parkes. In course of time the present gauge—the scale of which is very small—should be replaced by one of those which are used by Captain Baird, and an anemometer and a barometer (both self-registering) should be set up beside the gauge. But it is not desirable to interfere with the working of the present arrangements at Rurrachee until other ports, at which nothing is now being done in the way of tidal observations, are duly provided for. At Bombay, Carwar, and Madras, instruments are now being set up by Captain Baird.
VI.-The Application of Photography to the Reproduction of Maps and Plans by Photo-mechanical and other processes.—By CAPT. J. WATERHouse, B. S. C., Assistant Surveyor-General of India.
This paper was originally submitted to the Geographical Congress at Paris in 1875, but as the Proceedings of the Congress have not been published and the paper may be of interest to Members of the Society, as giving an account of the photographic operations for the reproduction of maps, now so largely employed in this country, I have carefully revised and to a great extent re-written it, so as to bring the information up to date and hope that it may not be considered too much wanting in novelty or too technical for the Journal.
Among the many useful and important artistic and scientific applications of photography, one of the most valuable is the reproduction by its means, in absolute facsimile, of maps and plans, speedily and cheaply and on any scale—either the same, larger, or smaller. So fully are these advantages appreciated, that most civilized States now possess special photographic studios for the reproduction of maps, plans, &c., for fiscal, military and other purposes.
Before the introduction of lithography, about the beginning of the present century, the only means by which maps, or indeed, pictorial subjects of any kind, could be reproduced, was by engraving on metal plates or on wood, both tedious and expensive methods.
With the invention of lithography, a new impetus was given to cartography by the comparative ease with which maps could be produced and multiplied by direct drawing or transfer on stone. The young art was, however, scarcely out of its cradle when Joseph Nicéphore Niepce, of Chalons-sur-Saone, experimenting unsuccessfully in endeavouring to find a substitute for lithographic stone, conceived the happy idea of obtaining images on metal plates by the sole agency of light upon thin films of asphaltum or bitumen of Judaea—and thus produced the first permanent photographs by a method of heliographic engraving, which, with a few modifications, still serves to produce excellent results; and it is worthy of remark in connection with our subject that Niepce's first essays were in reproducing engravings. Since these first essays of Niepce, the idea of superseding the slow and laborious hand-work of the lithographic draftsman and engraver by the quicker, cheaper and more accurate processes of photography, has been steadily kept in view, and various modes of engraving, both for copper-plate and surface-printing, and of lithography by the aid of photography, as well as other special photo-mechanical processes, have been introduced from time to time with more or less success, till at the present time these methods have taken a high and important position among the graphic arts, and as they steadily progress towards perfection, are rapidly extending their artistic, scientific and industrial applications. The attention of cartographers was very soon drawn to the advantages that might be gained by the employment of photography for the reproduction of maps and plans, but for some time progress in this direction was hindered by the difficulty of obtaining accurate images, free from the distortions caused by imperfect construction of the photographic lenses then employed. The first serious attempt to carry out the method practically appears to have been made, in 1855, by Colonel Sir Henry James, R. E., Director of the Ordnance Survey of Great Britain and Ireland, with the object of obtaining accurate reductions from the large-scale surveys more expeditiously and with more economy than could be done by means of the pantograph. The result proved incontestably the great value of photography for this purpose and the enormous saving in time and money that could be effected by its use. The possibility of producing absolutely accurate photographic reductions was questioned in Parliament, but Sir Henry James satisfactorily showed that the employment of photography produced reductions more accurate than could be obtained by any method previously im use ; that the maximum amount of error could scarcely be perceived, and was much within the limit of the expansion and contraction of paper under ordinary atmospheric changes—which was all that could be desired,
For some time, however, the use of photography in the Ordnance Survey Office appears to have been limited to obtaining accurate reduced prints for the engravers to trace from on to their copper-plates, and was not extended to producing maps for publication, owing to the expense and comparative slowness of production of photographic silver prints, compared with the lithographic or copper-plate impressions, to say nothing of their want of permanence. Experiments were next made with some of the so-called carbon processes, then recently discovered in France by Poitevin and first worked in England by Pouncy, with the object of transferring the photographic design at once on to the copper-plate, instead of tracing from the photographs by hand. The results obtained were not very satisfactory and a trial was made of Mr. Asser's photolithographic process, which had been published shortly before. Although this process was not found quite adapted to the purpose intended, the advantages of a method whereby facsimile prints in lithographic ink might be obtained and transferred to zinc or stone, so as to permit of a large number of copies to be printed off as easily as from an ordinary lithographic transfer drawing, and with precisely the same advantages in respect to cheapness and permanence, were obvious ; and in 1860, after several trials, Captain A. de Courcy Scott, R. E., who was in charge of the photographic operations at Southampton, perfected the process of photozincography, which has since been employed with so much success and advantage at the Ordnance Survey Office, Southampton, and in this country at the Survey Offices in Calcutta, Dehra Dún, Púna and Madras, as well as at other public and private institutions in other parts of the world. By a curious coincidence, at the very time when this process was being worked out in England, Mr. W. Osborne, of Melbourne, Australia, independently perfected an almost identically similar process of photolithography, which has been extensively used in the Crown Lands Offices of Victoria and Adelaide for reproducing the maps of the Australian Surveys, and has also been worked commercially by Mr. Osborne in Europe and America. These two processes, appear to have been the first instances of the practical application of photography to the reproduction and multiplication of maps for publication. They still remain, however, very extensively used, and are by the simplicity, cheapness and rapidity of their operations and the facilities they offer for the reproduction of maps of large size, of greater practical value than other processes which have since been brought forward with the same object, and are perhaps capable of producing finer results within the limits of a single negative. In India, the ever-increasing wants in the way of communications by 'ail, road and river, and the rapid extension of irrigation and other engineering projects, as well as the ordinary military, administrative and fiscal requirements make the early production of accurate maps a matter of very great necessity and importance, and as skilled lithographic draftsmen and engravers are scarcely to be obtained and must be trained as required, or brought from Europe at great expense, the subject of photographic reproduction as a means of quickly producing and publishing copies of the original maps of the Surveys, is much more important in this country than it is in Europe or other countries where skilled cartographic lithographers and engravers are comparatively numerous. The success that had attended the introduction of photography at the Ordnance Survey Office for the reproduction and reduction of maps immediately attracted the notice of the Surveyor General of India, and the services of two trained sappers, with the necessary apparatus, having been obtained from England, a small beginning was made in Calcutta in 1862. Owing to difficulties experienced in working photolithography in the peculiar climate of Calcutta, and the unsuitability of the original maps for reproduction by the process, owing to their being coloured and brush-shaded, little advance was made in the practical working of photolithography or photozincography in India till 1865, when Mr. J. B. N. Hennessey, of the Great Trigonometrical Survey, who had devoted part of his furlough in England to going through a practical course of instruction in photozincography at the Ordnance Survey Office, Southampton, fairly established the process at the Office of the Superintendent of the Great Trigonometrical Survey at Dehra Dún. I and other officers of the Survey Department were trained under Mr. Hennessey, and, in 1867, photozincography was finally started in Calcutta by Capt. A. B. Melville, who officiated for me during my absence on furlough, and since 1869 it has been carried on under my own supervision. Photozincographic offices have also been established under the Bombay Government at Púna, and at the Revenue Survey Office in Madras for the reproduction of the maps of the Revenue and Settlement Surveys in those Presidencies as well as miscellaneous work for other departments. In both of these offices the Southampton process of photozincography is used with a few modifications, but in Madras photolithography is also used with equally good results, and is, I am told, preferred for very fine work. Before the introduction of photography the publication of the results of the Surveys by the Surveyor General's Office could only be accomplished by the ordinary methods of lithography and engraving ; and though much good work was done in the former manner by the very limited native agency available in this country, many maps had to be sent to England to be lithographed, while the whole of the engraving connected with the Atlas of India, on the scale of 4 miles to one inch, was done in England under considerable disadvantages. Even with this help it was found quite impossible that