The Optical Magic Lantern Journal (June 1896)

96 The Optical Magic Lantern Journal and Photographic Enlarger. since that time in perfecting the apparatus for lighting by acetylene gas. If no progress has been made, the Italians are before us, for apparatus for the purpose (Sistema Frosali) may now be bought both in Roms and here in’ Florence. Five pounds is the retail price for a gasometer, with all things necessary for the manufacture of gas for the supply of fifty jets, and the operation is simplicity itself. A little water is poured into the gasometer, the charge of carbide dropped into the container, and the cover fastened down; the gas comes off freely, and its supply is regulated automatically. The carbide costs 80 centisimi a kilo (rather less than 4d. a pound), and half a pound (2d. worth) will supply one jet for 44 hours. As to the quality of the light, it is intense, pure, steady and white, not unlike the electric light. Four jets of it in a shop in the Piazza Signora rivals in brilliancy the arc light which hangs outside not far distant; at any rate the gas seems destined to compete with the limelight for the lantern. The proprietor of the shop assures me it is perfectly safe, and the fact that the apparatus stands at work in his shop, which is often full of people, proves his own faith in it, and there is not the slightest odour from it when burning 20: The Retort Courteous. A FEW years ago, during the progress of an oldfashioned stereopticon entertainment, in a town not far from Philadelphia, an incident occurred which not only gave the lecturer a good opportunity to make a clever retort, but also to rebuke a would-be funny fellow, who, during most of the evening, had proved himself an unmitigated nuisance. The audience had several times manifested impatience at the annoying interferences, but to no effect. Toward the close of the exhibition, says the Mzhibitor, the speaker began a description of the pictures which make up the dissolving effect known as “The Old Mill.” The view upon the canvas showed an old country mill, in midsummer, with the water-wheel in motion, and a swan gracefully swimming across the lake. The lecturer began asking questions, which the bird would answer by motions of the head. To one of these queries the funny fellow made reply, when the lecturer suddenly turned upon him and said, ‘‘I beg your pardon, sir; it was the goose on the canvas I was speaking to, not ” the one in the gallery.” The audience spontaneously broke into a storm of applause, and the discomfited interrupter soon after took his departure, along with several of his comrades. As they started for the door one of them remarked, loud enough to be overheard, ‘‘ He had you that time, sure, Billy.” :0: A Chat About Fog. (Continued from page 86.) By Duncan Moore. SUNSHINE will penetrate a considerable thickness of wood ; the position of an opaque body laid on it can be seen through two inches of deal in bright sunlight, provided the observer is in darkness, although the colour of the wood itself might act as a screen in a certain degree, and so make it practically innocuous as far as our plates are concerned. Still, ight will penetrate many substances sufficiently to injure photographic plates that are supposed to be light-tight, if the exposure toit is sufficiently prolonged. Verb sap. Development as a source of fog is tolerably well understood, and usually proceeds from the use of an unsuitable developer, or the improper use of a suitable one. It is impossible to i develop some plates with ammonia without pro ducing the well-known green fog, a dichroic abomination that used to be much more prevalent formerly than at the present time, ; possibly on account of the more general use of the fixed alkalies in the developer instead of ammonia, as when soda or potash are used it rarely occurs. Deficiency of restraining substance may also engender fog, or a too great proportion of the developing agents, as pyro, metol, etc., to the alkalies and restrainer. It has been suggested that white dishes that have been exposed to a strong light retain sufficient in a latent condition to fog a very sensitive film if used soon after removal from it; of course this would apply to any other white object recently removed from a strong illuminant, and brought into near proximity to very sensitive surfaces. Anyway, there is no doubt that very much greater precautions are required than formerly, if we are to steer clear of fog. Green fog by reflected and red by transmitted light, if only slight, has little effect | on the printing qualities of the negative ; some