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THE PHOTOGRAPHIC NEWS. Von. XII. No. 518.—August 7,1868. CONTENTS. PAGE New Substitute for Ground Glass 373 The Military School of Photography at Chatham 373 Echoes of the Month. By an Ohl Photographer 34 Short Essays on Photography and Art. By Nelson K. Cherrill 376 The Late M. Claudet 377 Pictorial Effect in Photography. By II. P. Robinson 378 On the Principles of Lighting and Constructing Studios. By Dr. Vogel 379 PAGE Notes on Development 380 On Nitroglucose. By M. Carey Lea 381 Correspondence — Photographic Notes on the Continent— Informers and Piracy: Graves v. Mercer—Photography and Disease 381 Talk in the Studio 383 To Correspondents 384 Registration of Photographs 384 NEW SUBSTITUTE FOR GROUND GLASS. A VARIETY of substances have been proposed, and some of them successfully used, as substitutes for ground glass as used in photography, cither for focussing-screens or as a backing for transparencies for the stereoscope. Our attention has been recently called by Mr. Woodbury to another, which is, we think, better than any that has been proposed or tried- The material proposed is not, indeed, new, but its applica tion for the purpose in question is, wo believe, new, as well as efficient. Mr. Woodbury proposes to use gelatine rendered semi opaque by the addition of a white pigment. This may be either applied direct to the front or back of the transparency, or it may be made in thin sheets and used as required. For stereoscopic transparencies this appears to us, from the ex amples we have seen, to give a better result than either ground glass, opal glass, or dull varnish. The ground glass, unless it be very fine indeed, when used with stereo scopes with powerful lenses, gives an unpleasantly sparkling or frosted appearance, and interferes with the delicate defini- nition of the picture ; and this is true, but perhaps in a less degree, of the dull varnishes, Opal glass generally ob structs too much light, but it gives a delicate soft effect to the picture. White pigmented gelatine gives an effect scarcely distinguishable in kind from opal glass, but as it can be used in a much thinner and more transparent layer, the softened delicate effect can be obtained without dullness ; in fact, the degree of opacity is quite under the control of the photographer himself. ■ For focussing-screens we cannot imagine anything better. All photographers who use an cyc-piece in focussing, in order to secure the greatest sharpness, are familiar with the diffi culty they experience from the grain or texture of the ground glass being magnified, rendering the focussing of fine detail difficult. The infinitesimally fine particles of white pig ment which produce the semi-opacity of the screen when formed of this substance will in no case confuse the finest definition, even under very high magnifying power. The one disadvantage which a screen of opal gelatine may possess would arise from the ease with which it may be soiled or scratched ; but this may be prevented to a consider able extent by treating the gelatine with a solution of alum, which will render its surface bard and insoluble. For preparing sheets of opalizcd gelatine the formula ugedby Mr. Burgess in his eburneum process will answer admirably ; it stands as follows:— French clear gelatine 5 ounces Water 20 Glycerine } ounce Oxide of zinc ... ... 1 After soaking the gelatine in the water for a few hours it is dissolved by gentle heat, and then filtered through flannel. The zinc white is placed in a mortar with the glycerine and one ounce of the water, and made into a soft paste. It is then stirred into the warm gelatine, and allowed to stand for a couple of hours, keeping the solution warm to allow the coarser particles to settle to the bottom ; the upper portion is then carefully decanted to get rid of the sediment, or, if it be allowed to cool and become a jelly, a slice can be cut off the bottom, removing all the coarse particles. Where the photographer desires to make the sheets for use it will bo wise to use up bis solution at once, as it will not keep well, especially in hot weather. Where he wishes to keep it at hand ready to coat glasses, its keeping properties may be improved, and decomposition arrested, by the addition of a trace of carbolic acid, or a little essential oil of cloves will help to preserve it. Or if it be desired to keep the mixture ready for use on redissolving, it may be poured out on sheets of glass and allowed to dry; it may then be cut up into strips, and kept as dry opaline gelatine, which can be readily redissolved on adding the proper quantity of water. We may add that it is Mr. Woodbury’s intention, we believe, to prepare sheets of opaline gelatine ready for use, and supply them to photographers commercially. THE MILITARY SCHOOL OF PHOTOGRAPHY AT CHATHAM. On the occasion of a recent visit to Chatham, we availed ourselves of the opportunity to visit the military school of photography at that town. The school forms part of the Royal Engineer establishment at Chatham, an institution established for imparting instruction to officers and non commissioned officers of the Royal Engineers in all branches of "technical education. Surveying, construction and esti mating, fortifications, telegraphy, and photography are the principal subjects taught, and these in a theoretical as well as practical maimer ; all young officers, on first joining the corps, being first ordered to Chatham to undergo a course of scientific instruction at the establishment before they are despatched to various stations to enter upon their ordinary duties. At the present moment, H.R.H. Prince Arthur, who has recently been gazetted to a lieutenancy in the Royal Engineers, is pursuing his studies at Chatham, and is going through the same course as that prescribed for all Engineer officers. Instruction in telegraphy and photography is imparted under the superintendence of Captain Stotherd, R.E., the latter subject being taught by Serjeant Instructor Church, to whose immediate care the whole of the arrangements con-
