The Optical Magic Lantern Journal (April 1896)

The Optical Magic Lantern Journal and Photographic Enlarger. Oil Lamps. By THE SHOWMAN. —S Ir would be exceedingly interesting to know what proportion the number of oil-lit lanterns gold bears to the total numbers which each year find their way into the hands of users. Unfortunately there are no figures available on this subject, but it may be taken for granted least half as bright as the other. From this we | learn the value of concentration in any radiant intended for optical purposes, The flame of the colza lamp is cylindrical in shape, and about 12 of an inch in diameter, the petroleum | lamp flames occupying a cross-sectional area of about 2 inches by ? of an inch; so that if the focus of the condenser falls in the centre of this area, it follows that the front edges of | the flames are an inch too close, and the back edges an inch too far away. that, even excluding toy lanterns, oil-lit lanterns — are greatly in excess of all other kinds. Before the introduction of the first modern form, which was known as the sciopticon, lanterns were generally fitted with a fountain lamp having an argand burner and glass chimney, and arranged to burn sperm or colza oil. Such lamps were very tolerable if properly managed and kept ' consequently efficient flames, other advantages scrupulously clean, and possessed the advantage over petroleum lamps that the fatty oils used ~ would most likely accrue. in them did not sweat or creep in the same way | as petroleum. On the other hand, if neglected . | focus objectives, and of being unable to tilt the they soon become clogged and covered with gummy oil, which nothing less than plenty of | The use of a long-focus lens necessitates the radiant being placed slightly nearer the con soda and boiling water would remove. Since the introduction of the sciopticon, a more or less stereotyped pattern seems to have | flame chambers of petroleum lamps as now been followed by all makers, with slight variations in the capacity of the oil tank, the number, width, and arrangement of wicks, the size and shape of the flame chamber, and shape and height of the chimney. If we take one of the best of these lamps and test the light under | favourable conditions with a photometer, a reading of about one-hundred candle-power will probably be obtained. Now, if one of the oldfashioned argand lamps is available, clean it and get it to work nicely, and a photometric test will probably show it to be yielding a light of about : thirty candle-power. two lights then is as ten to three. the two lamps in similar lanterns, and arrange the lanterns so as to give two discs side by side upon the screen. The discs should be of the same size, or rather, the projections of two slides having similar mounts should be of the same size when in focus. Be careful that the two objectives are of the same diameter and form, and are not fitted with stops. gain definition, handicapped the performance of the lamp considerably. Remove the slides from the stages, and look at the lighting of the discs. It will now be noticed that the ratio of ten to three no longer holds good, the disc from | the lantern containing the colza lamp being at | The relative power of the | Now place | If we examine the powerful oil lamps with which lighthouses are sometimes fitted, we find that the burners are arranged with several circular concentric wicks, and it is to be regretted that lantern makers do not pay attention to the possibilities of a miniature lamp with two wicks only on this principle. Were they to do so, and produce a lamp with concentrated and At present, users of oil-lit lanterns have to put up with the inconvenience of being confined to the use of short lantern to an angle of more than 4 ord degrees. denser, which with the size and shape of the made is an impossibility. Again, if a lamp be tilted to the extent which is desirable, not only will the tank prcbably overflow, but the flames will strike the front of the chimney. A lamp with a small compact flame chamber, fitting the flames in the same way as the glass chimneys of our domestic lamps, will by going closer to the condenser permit of the use of longer focus objectives than are at present employed, and will most likely allow of tilting to an angle of from 20 to 25 degrees. To prevent the oil from being spilt, the lamp should swing on a pair of gudgeons placed horizontally at right angles to, and on a level with the centre | zontal position owing to gravity. line of the optical system. These gudgeons should be supported by side brackets from a tray, to which the reflector would be fixed either permanently or with provision for adjustment, the tray sliding in the usual grooves in the base of the lantern. The lantern could then be set up horizontally and the lamp carefully Many of the old-fashioned lanterns were fitted adjusted, and the with objectives, which, being stopped down to | lantern then tilted the requisite amount, when the lamp would simply swing on its gudgeons and maintain its horiAs the gudgeons are on the optical centre line, the lamp would swing as it were on the centre of the flame, and the previously made adjustments would be in no way interfered with.