The Optical Magic Lantern Journal (February 1890)

66 it will afford those who possess and who Jove the working of the lantern, to send a set of slides to member A. B., and when they want to amuse their friends in the drawing-room, or give an exhibition publicly, to borrow a set in return from A.B. And what a fine thing, again, it will be for the members of this club if they can have some special tariff from the great slide-makers and dealers. In fact, looked at from whatever standpoint, it isa movement of the highest importance for this popular and rising instrument. * ® * In connection with the Newcastle-on-Tyne and Northern Counties Photographic Association, an International Photographic Exhibition will be held in the Central Exchange Art Gallery from April 18 to May 3; and at the same time and place a supplementary exhibition of photoapparatus, appliances, and mechanical printing processes. 0: The Magic Lantern : Its Construction, Illumination, Optics & Uses. CHAPTER IX.—GENERAL MANAGEMENT OF THE LIGHT. Oi, Licut.—It is a well-known fact that the same lantern outfit in the hands of exhibitors possessed of different qualifications may give either good or bad results according to the good or indifferent management it receives at the hands of the operator. Although it may at first appear a simple enough matter to ‘‘run”’ a lantern, yet to get.everything in readiness with dispatch, and to keep everything going smoothly throughout a lantern exhibition, requires a certain knowledge and deftness attainable only by practice and experience. In the case of oil illumination it is wholly under the control of the operator whether the lamp will give off an unpleasant smell or not, although too often the lamp itself is blamed when the fault should have been attributed to inexperience, or want of knowledge of the requirements of the instrument. The lamp and wick should be taken to the hall or room where it is to be used in a thoroughly dry and.clean condition, and the oil carefully poured into the reservoir by the aid of a funnel, not even the smallest quantity being allowed to go on the outside of the lamp. Until it is to be lighted, the wick must be kept turned down, and not allowed to protrude from the tube in which it travels, else will the oil, by capillary attraction, run down the outside of the burner, for it is surprising what a large surface a small quantity of Tho Optical Magio Lantern Journal and Photographic Enlarger. oil will spread over, especially after the surface is warm. The wick or wicks should be trimmed with scrupulous care, and no unevenness of surface must be allowed, as ragged edges cause “points” at the top of the flame, which will give off smoke before the wicks are properly turned up. This. also greatly diminishes the quality of light that would otherwise be attainable. When a lamp is turned up and is placed near the condensers—especially if the latter are very cold—it is not an unfrequent occurrence for them tocrack. It may be argued that the lamp can be turned down for a time until all the surroundings get warmed ; but it will be found that an oil lamp if turned below a certain point will emit the un-pleasant oily smell so much complained of in thisconnection. This point of limit in turning down varies according to the adaptation of the fittings. around the flame. The better plan fcr warming the condensers is, in the case of compound ones to unscrew the component parts, and warm them very gradually in front of a fire. The separation of the lenses. prevents the condensation of vapour in the space between the two glasses. The objective should also be warmed in like manner, and by the time this has all been done and replaced, the surroundings will have been. heated sufficiently to prevent condensation. When using a lamp of the Sciopticon class, the wicks on the outside should be turned up first both the same height, then the inside ones, and all adjusted just short of smoking. SAFETY OR BLow-THROUGH JET. This light is produced by a fine stream of oxygen: being blown through a flame, so as to make it impinge on a piece of lime, which thus becomes. incandescent, and throws out a powerful light. The flame may be produced either by pure: hydrogen gas, or by ordinary house gas, and as. the latter is, generally speaking, always at hand, we will consider that it is to be used for the production of the flame, although pure hydrogen will produce a slightly whiter flame. Still, the extra trouble of conveying a supply will hardly compensate for the slight difference in the quality of the light. The oxygen may be supplied either from a gas bag or from a cylinder containing the gas in a compressed state, but in cither case we will suppose that the supply is at hand, and will not deal. with the making of the gas. If the bag be of English make, the tap will be found to be at the wedge end, but in America many have the tap fitted at the wide end; not, however, that it makes any material difference.