The Optical Magic Lantern Journal (June 1896)

106 The Optical Magic Lantern Journal and Photographic Enlarger. years. The confinement of this lamp in a lantern has absolutely no deteriorating effect upon its burning, even when a focusing cloth is thrown over to prevent stray rays reaching the bromide paper when enlarging; and in connection with this I may say that so far from this light approaching what I have called a furnace, I find it possible to use the focusing cloth in this way during a pretty long exposure without singeing the cloth, and there is certainly no need of the alum tank. Throw a picture of 7 feet disc upon the screen, and you will note the purity of colour and steadiness of light. Note also a property which may be useful in the dark room, viz., that the light may be turned completely out for two or three seconds, and burn up again when turned on. In order to shorten exposures, and at the same time be enabled to give a lantern demon = } vost en — Jt Puan of Qevcen Firring ZA IMENTS , ee ie ee ee eso lS Innes ELcvarion oF Lance £ PUTING stration to a moderately sized audience such as this, I commenced to experiment by feeding oxygen into the lamp in the hope that an improvement would result. But I soon found that by mixing the gases in a Bunsen where air is present forms an explosive mixture, and is an experiment not likely to be repeated by any one who tries. I then determined to burn the oxygen outside of the lamp proper, and designed a burner for the purpose, which has been found to work well and safely. If you will kindly refer to the drawings, I will endeavour to explain its simple construction. The drawing is a semi-sectional elevation of the lamp, and the red lines show the general construction of the oxygen attachment. The oxygen comes from the cylinder, per regulator, in the usual way. After passing the check stopcock, it passes through perforations in the end of a tube, which spread the gas within the burner, and finally the gas emerges through very fine perforations on the top of the burner at a low pressure, and acts by stimulation of the incandescence on the part of the mantle next the condensers. The burner and a portion of the supply pipe is fitted to the top of the lamp by an annular ring, and may be removed by unscrewing the union joint should the remaining part of the fitting require to continue fixed. The whole apparatus, however, may be removed by unscrewing the pinching screw which secures it to the foot of the lamp, so that by means of these arrangements the oxygen part can be added or be dispensed with as occasion requires. When in position, the top of the oxygen and hydrogen burners should be about the same level, with a space of from {; in. to 4 in. between them, into which the foot of the mantle slips. During my first experiments with oxygen in this way, I was troubled by finding that the most brilliant part of the mantle sometimes faced the back or a side of the lantern, away from the condenser, with the consequent darkened field upon the screen. To meet this erratic habit, I thought of fitting a turn-table on the Welsbach fitting. After repeated experiments, however, I found the best way to cure this is to block out the rear portion of the mantle by means of a hood of platinum foil placed inside the mantle, and held in position by the ring which supports the oxygen burner. This is a ‘‘ perfect cure,” as it not only concentrates the light to the front, but enhances its illuminating value, and also helps to steady the mantle without doing it injury. I may here say that this is a most essential part of the apparatus, and one which I claim as quite novel. When we come to consider the photometric values later on, you will be better able to appreciate what I have just described. It is needless to deny that the fragile nature of these mantles is very much discounted by the public ‘generally, and especially those who have not tried or given them fair play. For instance, the mantle sold by the Company is, as a rule, too long, or, as the ladies say, too ‘‘ deep in the skirt’; but in order to adapt it for this lamp, I usually clip fully half an inch off the bottom, which has the etfect of preventing splitting and fraying, so common in ordinary lamps. One of the chief fears I had for the success of the oxygen fitting was the interference with the air passage between funnel and mantle, but I find no deterioration whatever. In fact, in the course of my experiments, I have disturbed and