The Optical Magic Lantern Journal (December 1892)

152 perhaps it will in most cases do, is not theoretically correct, and, to be so, the equivalent focus of the lens employed should be added to the result obtained by the above calculation. A few days ago we were afforded a treat by Mr. Hill, the well known slide artist, of 18, Beversbrook Road, Tufnell Park, N. This gentleman showed us a number of lantern slides he had painted in the old Polytechnic days, at which time his firm (then Childe & Hill) painted most of the slides used at that Institution. Many sets of the present time were also shown to us ; the sketches, which themselves were works of art, were made on the glass, and those in a completed state were of the highest class we have seen, being totally different to a coloured photographic lide: Tuis is the time of year when Seuatbid complain that the fog prevents their light from penetrating across a large hall; the best remedy in such a case is to bring the apparatus nearer to the screen, using a lens of eumeyie focus. Douxixna some s Pelenmants with a Lucigen light of 9000 c. p. in a fog, it was ascertained that it could be seen at a distance of about 1000 feet. at x a A smart bit of work was performed at the Hackney Photographic Iixhibition on the 17th ult. Among the exhibits of apparatus, etc., were the Platinotype Company’s new lamp for printing at night, and the Paget Prize Plate Company’s new printing-out lantern plate. A negative of the worthy secretary was obtained, and with the above-mentioned articles a lantern slide was printed, and shown upon the screen, quiring more than two unANtes: WiTH the ae Number we en Volume TI. of this Journal; the Index will be issued with the January Number. We take this opportunity of thanking correspondents in various parts of the world for their good wishes, which are continually pouring in upon us. © Itis gratifying to learn that we have such a wide circle of friends and supporters, and pleasure in wishing our readers A Mrrry CunistMas. A number of first-class lantern exhibitions are to a great extent spoiled by the use of a bad signal for changing the slides. Antnur K. Deanpry. I (at New York) was the first to adapt and introduce | the bellows collapsible extension front for lanterns, applying it in 1876, but unfortunately did not patent this application, and it is now extensively used. T. H. McALwisten. have , Y ‘ about half an inch The Optical Magic Lantern Journal and Photographic Enlarger. Old Coal Gas. WHILST oxygen or (pure) hydrogen will keep for an indefinite period when compressed in cylinders, and when used at any distant time be found to act in a similar manner to gas of more recent manufacture and compression, coal gas appears to undergo a chemical change after being kept for a few months, to such au extent, as to render it quite unsuitable for practical purposes connected with the production of the lime-light. We recently received from a well-known lanternist, a lime cylinder, which had been used in conjunction with coal gas which had been bottled for six months, and were supplied with particulars of its behaviour when used in the lantern. Whilst the lime was new and clean, it was, with a blow-through jet, at once rendered . Incandescent ; but in the space of a very short time the incandescent spot became less brilliant, whulst a red deposit appeared on the lime. This deposit speedily changed to black at the immediate point of the line upon which the gas impinged. The red _ precipitate gradually enlarged over the surface of the lime followed by the black, and the lime became no longer incandescent to any great degree. What light © that was obtained came by a series of jerks. After examination of the jet, it was found to be incrusted with a fine brown compressed powder, which could be readily removed. When the jet was cleaned, and the lime scraped, an ordinary light was again obtained for a short tine. Respecting the chemical action set up between ' the coal gas and the cylinder, we will not at the whole operation not re— present offer any explanation, as_ several scientists are at present engaged upon an investigation of the subject. However, it may in the meantime be well to state how one may be able to ascertain if any particular cylinder of coaligas, which has been kept for a long time, has deteriorated, or that it will behave in a similar manner to that just mentioned. Ii the valve of a cylinder of old eas be slightly opened, and a light applied to the gas, the flame when tuned down to high, will exhibit four distinct cones of flame of slightly different colour, one being within the other, whilst, if the light be still further turned down, the central cone will rise above the others, and appear of a yellowish colour with smoke at the top. It is impossible to make a perfect lantern condenser with less than three glasses. J. UYrat.y Payton.