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THE PHOTOGRAPHIC NEWS VoL. XXVII. No. 1290.—May 25, 1883. CONTENTS. PAGE Photographic Action Studied from a Spectroscopic Point of View 321 On the Suitability of Geiatino-Bromide Plates for Rembrandt Effects 321 Half-a-Dozen Portrait’s" 322 Erench Correspondence. By Leon Vidal 324 What is a Restrainer ? By A. L. Henderson 324 Photo-Lithography and Photo-Zincography. By Major J. Waterhouse", B.S.C 325 On Transparencies by the Carbon Process. By Edward Brightman 326 PAGE Notes 328 Patent Intelligence 33° Twelve Elementary Lessons on Silver Printing 330 American Photography “ As it Was.” By W. M. Ashman ... 332 Apparatus for Printing by the Blue Process. By Channing Whitaker 333 Correspondence 334 Proceedings of Societies 33 Talk in the Studio 336 To Correspondents 336 Photographs Registered 36 PHOTOGRAPHIC ACTION STUDIED FROM A SPECTROGRAPHIC POINT OF VIEW. A discourse delivered by Captain Abney before the Chemical Society on the 17th instant served to give the members a general idea of the direction in which the Captain has been working of late. TThe lecturer expressed regret that a larger proportion of chemists do not take sufficient interest in photography to make themselves become photographers, even if on a very modest scale; but, at the same time, it is desir able that photographers should become chemists. The difference between chemical and the so-called physical development was first explained, after which physical development was illustrated, by exposing a sheet of iodide paper, and developing an image by means of gallic acid and nitrate of silver, and it was shown how the deposited silver might be dissolved off by means of nitric acid, leaving the film much in the same condition as originally. No effect of light could be traced unless a sensitizer—that is to say, some substance capable of taking up the liberated halogen—was also present, and the sensitizer might—at any rate, from a theoretical point of view—be either an organic compound or an inorganic body, mercury vapour having acted as a sensitizer in one instance. A tube con- taining dry and pure chloride of silver, which had been frequently exposed to the light, was shown, the salt being still quite white. Chemical Development—to use the ordinary term—was next practically illustrated, the citro-oxalate of iron developer being used; and it was pointed out that in this case the silver forming the image was that originally in the film, while treatment with nitric acid would leave the film denuded of a considerable proportion of its original haloid salt. Energie diagrams, showing the photographic action of the solar spectrum, and of that of the positive pole of the electric arc respectively, were projected on the screen, and the uniformity of the latter was certainly such as to suggest its superiority for adoption in photographic investigation. The Rowland concave diffraction grating was referred to as a valuable aid in spectrographic research ; but they are subject to variation, one grating giving but little ultra violet, while another was deficient in ultra red, and it is frequently necessary to select one for the special work to be done. The absorbtive powers of bromide, iodide, and chloride films were next made visible by means of the optical lan tern, and it was clearly shown how silver iodide tends to cut off the violet; bromide the blue and violet, while chloride cuts off considerably less of the spectrum.’ Most work is done by light on the bromide; the iodide comes next; while in the case of chloride least work is done. This I condition of things was well illustrated by photographing a spectrum on each one of these haloid salts, the bromide giving a very prolonged image, while the iodide was about one-third shorter, and the chloride was about one-fourth the length of the bromide spectrum. Not only is the comparative insensitiveness of chloride notable, but the difficulties of properly restraining it during development are consider able. The influence of sensitizers was demonstrated by partially treating a bromo-iodide film with a solution of sodium sulphite and exposing; while the action of certain colouring substances as sensitisers was alluded to. De sensitizers, such as oxidising or haloidising agents, were then discussed, and it was shown that no image could be impressed when these were present in sufficient force; and the practical value of the bichromate process as a remover of fog was elucidated by the exhibition of numerous in teresting specimens. • ON THE SUITABILITY OF GELATIN O-BROMIDE PLATES FOR REMBRANDT EFFECTS. Some years have elapsed since the photographic fraternity were made familiar with what seemed to some an innova tion in the mode of lighting a portrait model. Dogmatic writers went beyond calling the new system by such mild terms as inartistic, unreal, &c., and even went so far as pro nouncing the effects produced to be diabolical. So loud was the denunciation, that, had it not been for the opposing forces brought to bear by those who were more capable of judging the possibilities and advantages to be derived by the change, it is somewhat doubtful if the public would have been the happy possessors of so many examples as now. Fortunately, the adverse opinions then expressed were not heeded, for several well-known portraitists gave the subject their especial attention, with the result that a great advance was made, and fully appreciated by the public; to wit: higher prices were charged and obtained easily ; the number of patrons increased ; higher salaries were paid to the staff ; congratulatory communications instead of derogatory were addressed to the principal by his clients, thereby raising the status of portrait photography at least one step higher on the pinnacle of fame. Among those who built up a lasting reputation for the delicacy of modelling rendered in the production of large heads, may be mentioned the late Oliver Sarony, of Scar borough. Cabinet heads photographed in the Rembiandt style by this talented artist have found their way into all civilized parts of the universe. Mr. Fergus, of Largs, Scotland, for some time devoted a great deal of attention to this style of lighting, and so great was his success in obtaining Rembrandt effects, that Mr. Baden Pritchard deemed the studio at Largs of sufficient im portance to describe it first among his Scotch studies. He