The Optical Magic Lantern Journal (July 1895)

114 The Optical Magic Lantern Journal and Photographic Enlarger. of a tuning fork kept in motion by means of electricity. The drops of water composing the jet were thus broken up into a distinct order varying with the note used. To the eye little change was seen, but when an intermittent shadow of the drops of water was cast upon a white screen by the stroboscope the distinctive forms of the drops of water comprising the jet could be easily seen by the audience. If only one person is to see the phenomena the lantern can be dispensed with and the eye placed near the holes of the stroboscope and viewing the fountain against a bright bdckground—for instance the sky. It is curious to notice, in showing these experiments, that the drops of water gradually appear to begin to fall more slowly as the flashes of light are allowed to fall more rapidly. The drops form and break and continue to appear to fall downward more slowly, so that the drops of water will be seen, if the right speed of rotation is obtained, to form a neck which will gradually get longer and thinner until it breaks and divides itself into two large drops, with the waste portion hreaking up into two and sometimes three small drops. When the rapidity of the flashes of light are still more increased, the drops of water will appear to be returning into the nozzle of the jet instead of the direction in which they are really going ; by placing your finger in the path of the jet your mind will be soon set at rest on that point. Those who are interested in the foregoing experiments cannot do better than get a copy of Professor Boys’ ‘‘ Book on Soap Bubbles,” where they will find a large number of experiments like the previous, and by carefully studying it their field for the wider application of the lantern will be much increased. Professor Tyndall's ‘¢ Book on Sound” also contains many experiiments like the one above mentioned, suitable for demonstrating with the lantern. Another ingenious application of the principle of the stroboscope to the microscope is by Hopkins of New Ycr«, and consists of a small metal diaphragm witha number of ‘holes equidistant from the edge, operated by a small electric motor and fitted below the substage of the microscope. It will, he says, be found useful for showing more distinctly the motion of those small aquatic insects whose action of the parts of their body are so rapid as not to be able to be discerned without its aid. One can see no reason why it should not be fitted to a lantern microscope also. When once the principle has been grasped—which will soon be done after a few experiments--many uses will be found for it which will readily suggest themselves to the reader. Light. INTERCEPTED CORRESPONDE NCE. S1k,—I trust you will pardon the liberty Iam taking in addressing you thus, but your eminence in lantern matters isso great and your kindness and condescension so well known, that I venture to ask your help and opinion on @ difficulty with which I am troubled. Briefly, it is this, although my optical apparatus is high-class and every care is bestowed upon it, I frequently fail to get a good light with it. If you can spare time to give me a hint or two I shall be extremely obliged. In anticipation, Gratefully yours, A.B. GINNER. BomBastes TRIPLE, Esq. My Dear Srr,—Although extremely busy I shall be delighted to extend you a helping hand and do what I can to solve your difficulties for you. My experience is always at the service of anyone who, like yourself, shows a due appreciation of my abilities. This communication to you would have been briefer if you had stated the particular luminant you have been using, whether oil-lamp, blow-through, mixed or saturator ; but as you do not mention which form you have adopted, I must give you a few hints on each. If you have been using an oil-lamp, let the very best oil and new wicks for each exhibition be your rule. Ascertain by experiment that your lamp is at its most effective distance from the condenser, and make sure that a plentiful: supply of fresh air reaches the wicks, and that its flow is unchecked either by want of perforations in the base of the lantern body, or by the shape or position of the chimney hood. You can easily ascertain the value of fresh air where oil-light is concerned by trying to show your slides in a stuffy unventilated room, you will find the lamp smoking and smelling long before the flame has been raised to.its proper height. It is more likely, however, that your efforts have been made with a blow-through jet. If the jet you have been using is constructed in accordance with recent ideas, %.e., with the oxygen nipple well sunk, and the flow of hydrogen unimpeded by too small a bore of tube, or by unnecessary turns in it, then you must seek the cause of failure elsewhere. Are you sure that the stream of gas impinges exactly in the centre of the lime? You can test this by turning on an excess of hydrogen and noticing whether the wing of flame on each side of the lime is fairly symmetrical. If this is not the case, bend or twist the nipple until the stream of gas does strike the lime exactly in its centre line, otherwise its heating power will be uselessly exerted in the wrong direction—on the lantern. body for instance. Again, there is