The Optical Magic Lantern Journal (June 1890)

6 The Optical Magio Lantern Journal and Photographic Enlarger. private company was soon formed to patent and | develop the brilliant idea. The light in question is essentially a chemical discovery rather than a mechanical idea, and consists of a peculiar tape that is fed by a simple clockwork. While it is peculiarly adapted to street or other stationary purposes of illumination, yet it is said to be also applicable to portable or hand lamps ; and in point of intensity it is not surpassed by electricity, its light is much softer, and far easier to the eyes. It feeds itself, requires neither pipes, wires, or other connections, and in size may be produced from 300 to 7,000-candle power. It is absolutely nonexplosive, emits no smoke or objectionable vapour, is applicable to any purpose. and can be handled with as equal safety by a child as by an adult.—CAzcugo Fournal of Commerce. ‘0: Asbestos Between Lanterns. I NOTICE that one of your correspondents asks advice about fastening the division in a biunial lantern. It may, perhaps, interest him and others to know that when I altered an old lantem some time ago to suit my requirements, I made the divisional shelf double, and filled the space with asbestos about an inch deep, with very satisfactory results. Small and compact lanterns are required, but so far as I can find out, there are none in the market. If ‘‘ Lantern” would finished, I feel assured our Editor would give us all the benefit of it.—RALPH TEMPEST. [We are always pleased to insert anything of a practical nature.—ED.! Experiments with the Optical Lantern.” WE are attempting too much to-night, and may make our excuses before wecommence. What weare trying to do has never before been attempted ; the changes in themselves are not troublesome, but the adjustments take some time and care. | feel at present as if we were commencing an unrehearsed pantomime, in which all the scenes stick, trap doors open under the wrong people, and the actors mix up their parts. All the demonstrations are simple enough in themselves, and would be comparatively child’s play if an evening were given to each form of apparatus instead of the constant changing and pulling apart of the different arrangements and re-adjusting them quickly, with precision. We will do our best, and when I inform you that both Mr. Furnivel and his son are in charge of the lanterns, those of you who have had experience will know that department will be properly handled. The object this evening is not to show you any Pictures or special experiments, but rather to demonstrate to those who have lanterns a few of the experiments which may be made, and show, not only how much amusement may be obtained, but also how useful the apparatus may be made for educational purposes. For many of the experiments we shall show nothing more is needed than the common lantern with a lamp, and the alterations which are necessary are very simple, and easily made by an amateur workman. * Warrington Literary and Philosophical Society. No doubt you are all familiar with the ordinary arrangement for showing slides, which consists of a source of light, which should be as small and intense as possible, a condensing lens which is made. of two plano-convex lenses to collect the light, and the obiective, which also has two separate lenses used to focus the image on the screen. The lens of the condenser nearest the light collects the rays and throws them ina parallel beam, the other lens collects this beam and concentrates it on the objective. If we unscrew the outer lens and remove it to any distance, we have in the space a parallel beam of light which. we can reflect and turn about in any direction, and then throw on the screen. You see on the screen a photograph of an arrangement of this kind, where the | parallel beam of light is reflected upwards by a mirror ‘placed in a box; on the top of this box is placed the outer half of the condenser with the flat side i upwards, and above this the objective at the proper : distance. If we place on the horizontal surface of the condenser any slide or picture, this is projected on the ceiling, or with another mirror it can be thrown onthescreen. Ifa pointed pencil or needle is used on this the pointer is also shown on the screen, and the lantern manipulator can lecture and use a pointer on the screen as easily as if he were at thé screen itself. The same arrangement can be used for showing vibrations of plates of glass covered with . : Paar: ‘ uid | sand, chemical experiments with shallow glass tanks, give his fellow-readers a description of his, after it is | : P bs experiments with magnets and iron filings, and endless other demonstrations in physical science. This method of dividing the condenser seems to be almost unknown ;. the usual way is to place the light dangerously near the lens, and so obtain a parallel beam, using an extra and costly condensing lens to collect the beam. As you will see, this is simply a waste of money. Another adaptation of existing parts will be found exceedingly useful. When a lantern is used, sometimes close to the screen, and at other times at a long distance, a necessity when the demonstration is given in rooms differing in size, it is usual to have costly objectives of different focal lengths. This is quite unnecessary. If we have, say, an objective which gives a 15ft. picture twenty feet from the lantern, by removing the back lens of the objective and setting the light nearer the condenser we shall get a 15‘t. picture about forty feet away ; if we remove both, and place the back lens in front, we shall get a 15ft. picture eighty feet from the screen. This enables us to work in rooms of any size, and obtain any size pictures we require with thesamelenses. There may bea difference in lenses ; the distances given are from my own. There is one little objection to this as regards the ordinary lantern in the fact that the objective requires to be brought much more forward, but it is a simple matter to: separate this from the lantern body and mount it on a separate stand; in fact, this must be done before other experiments can be performed, all lanterns for physical demonstrations being made in this manner, and mounted on a long board with guides for placing the various appliances correctly in the centre. Replacing the lenses in their ordinary position, we will put in the slide carrier a plate with a narrow slit in it to get a thin line of light ; before this we will place a prism which throws the spectrum on the screen, show-ing the decomposition of light. THOS. FLETCHER. (To be continued.)