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520 THE PHOTOGRAPHIC NEWS. [July 17, 1891. The president, Mr. J. W. Marchant, then addressed the members, pressing upon them not to hoard up knowledge, but to impart it freely to each other, and upon those beginning the study of photography to make known their difficulties, and to ask for information. Four new members were elected. Sydenham Camera Club. July 1th.—The President in the chair. A paper on “Home Portraiture” was read by Mr. J. Goldfinch, in which some valuable suggestions were given as to the lighting of the subject. He mentioned that a plaster bust was a very good object to try effects of lighting on, as it could be placed in whatever position wished, without tiring the sitter. He also went fully into various dodges to be resorted to in default of a studio, described the lens and camera, the best plates and developers to use, backgrounds, &c. Hackney Photographic Society. July 9th.—Mr. Beckett in the chair. Mr. B. Foulkes Winks read a paper on the “ Details of Silver Printing,” going through all its stages from sensitising the paper to the mounting of the finished print. Saturday, July 11th, was a hand-camera day down the river. Sheffield Photographic Society. July 1th.— Mr. B. J. Taylor in the chair. After routine business, Mr. T. J. Hibbert brought for inspection the automatic hand-camera by G. Houghton & Son, fitted with one of Wray’s lenses. Several members brought copies of prints taken at the recent excursion to Lincoln. Mr. E. Beck then gave a practical demonstration on “ Platinotype Printing ” by the hot-bath process. It was arranged to have Saturday afternoon excursions as heretofore. Oxford Photographic Society. Ox July 7th the new rooms of this Society were opened, and will remain open each day, except Sundays, from 10 a.m. till about 9 p.m., for the members’ use. There are already numerous photographic papers and books on the table, and it is hoped that the walls will soon be covered with photographs. It is requested that all communications for the Society be addressed to the Hon. Secretaries, Photographic Society, 136, High Street, Oxford. Photographic Club.—Subject for July 22nd, “Salting and Sensitising Photographic Papers”; 29th, “Developing en route.” Outing on 18th at Welwyn ; train from Moorgate Street at 2.15. Phosphorescence of Minerals.—Various forms of fluorspar from various sources were excited by light, heat, and the electric spark, and the spectrum of the phosphorescence was examined. Measurements of the wave-lengths of the bands are given. In the phosphoroscope, the bands that are visible or have the highest intensity vary with the speed of rotation of the disc, a result due, according to the author, to differences in the persistence of the phosphorescence of the various substances that are present in the fluorspar, and give rise to the different spectra. The electric spark excites phosphorescence in the same way as sunlight, and the spectra are the same. The effect is more intense with the spark than with sunlight, probably because of the high proportion of rays of high refran- gibility in the former. When fluorspar is heated, a limited quantity of energy is set free in the form of luminous vibrations, but if the heating is continued the phosphorescence ceases. It can, however, be restored by exposing the substance to light or the electric spark. The bands in the spectrum, when the substance is heated, have the same positions as in the phos phoroscope, but they have different relative intensities. The relative intensities also vary with the temperature. Phosphor escence under the influence of heat belongs, in fact, to the same class of phenomena as phosphorescence excited by light.— Compt. Rend. Answers to Corresponents- All Communications, except advertisements, intended for publication, should be addressed to the Editor of the Paorognaparc News, 5, Furnival Street, London, E.O. All Advertisements and communications relating to money matters, or to the sale of the paper, should be addressed to the Publishers of the PHOtoGRAPatC News, Messrs. Piper & Carter, 5, Furnival Street, London. Questions requiring a reply in this column should be addressed to Mr. John Spiller, F.C S., 2, St. Mary’s Road, Canonbury, N. C. A.—Question of Copyriyht. In the case which you put to us, the wholesale piracy of a series of copyright portraits in the manner indicated is clearly not lawful ; but it might be possible to arrange for the assignment on easy’ terms, for your special purpose, of the copyright of the individual photographs composing your group, particularly as they would have to be reproduced on a much smaller scale. But the fact remains that a copy of any size is held to be an in fringement of the owner’s rights. The law of the case is clearly defined in Mr. G. Fleetwood Pritchard’s article on page 87 of the Year-Book. F. D. T. (Edinburgh).—CoUodio-Chloride Emulsion. The cellular structure of your collodion films possibly arises from the circumstance of their containing too much extraneous salt—the by-product of double decomposition, sodium nitrate, &c. To overcome this defect, it would be advisable to emulsify a ready-formed chloride, or wash the emulsion as practised in the case of gelatino-bromide. The use of a highly glazed enamelled paper might enable you to succeed even with your existing preparations, but the other course is preferable. 0. C. (Bournemouth).—Litho Presses. We are sending you the address of a London firm from whom they can be pro cured. L. li. 0. (Whitchurch).—Photo. Enamels. Messrs. Sharpus, McCullum, and Co., of Cockspur Street, Charing Cross, will supply them. St. Mungo.—Silver Residues. Salt will precipitate the silver from print washings ; but all the waste hypo solutions should be mixed together and treated with hepar sulphuris until all the silver is thrown down as sulphide ; best done on the roof or out of doors. Collect on a filter and send to the refiner, or reduce it by fusion with carbonate and nitrate of soda. H. B. G.—Sulphuration of Prints hy India-rubber. The practice of laying vulcanised rubber against the surface of silver prints, wet or dry, is not to be recommended, for the least trace of sulphur or sulphides is apt to cause a dark stain, as it will do even in the case of silver coin. The advice given in the printed account (keeping prints flat) is very good, with exception of this one particular. Bradford.—Oldfield's Multi-Colour Apparatus. The specimen sent out with the prospectus is satisfactory, and reference is made to Patent Specification No. 9,302, a.d. 1889, from which you can doubtless gather further particulars. The invention has, however, nothing to do with chromo-photo- graphy, unless you can establish such a connection. M. W. (Colchester).—Photo-Traininy. Spotting and mount ing, book-keeping or reception-room duties, and even print ing, is sometimes undertaken by ladies. You might offer to give time in return for instruction in these branches, and, when competent, you can of course submit your qualifications by advertisement. Second letter received. C. N. & Co.— Yellotv Marics in Printing. The most fertile source of such defects as those shown in your print is the injudicious handling of the paper in the early stages by fin gers contaminated with hypo. We do not think they are due to bubbles or matting in the fixing bath. F. I. C.—Some Recent Advances in Photography. The lecture recently given by Mr. C. H. Bothamley at the meeting of the Nottingham Section of the Society of Chemical Industry is reported in the current number of the official Journal. It deals chiefly with the primuliue, Feertype, and kallitype processes, and their latest modifications.