The Optical Magic Lantern Journal (October 1893)

152 The Optical Magic Lantern Journal and Photographic Enlarger. reach of meddlesome students. The lanternist can be communicated with by the lecturer either by means of a speaking-tube or by an electric bell. Pictures projected upon this ground glass show up exceedingly well. The ground glass used in this method is, of course, expensive, and also likely to be broken; for this. however, might be substituted various other semi-transparent media, such as oiled linen, paper, &c., but the results would not be quite as satisfactory. For class demonstration, the lantern, and all apparatus belonging to it, should, if possible, be placed out of the reach of students, as interference with it is exceedingly dangerous. This is frequently possible, even under ordinary circumstances. The plan just described, how ever, has an additional good poiat, viz., that the boxes containing the slides can be always within reach of the lanternist,'so that he ‘is able to exhibit one from any series as required. In the modern lecture-theatre, in which the seats are raised one row above another, the | lantern can sometimes be manipulated from beneath them, in such a way as to be quite hidden from the view of the class, The cut will explain the arrangement. The question may now be asked: Can the exhibition of diagrams and photographs by means of the lantern entirely replace the older and more frequently adopted methods of illustrating lectures? The answer will certainly be in the affirmative, for not only does the , lantern do its work better, but it has many and distinct advantages over any other method. One of the distinct advantages which diagrams are said to possess over lantern-slides is that they can_ be examined for a greater length of time, and can, if necessary, be copied after or during the lecture. This is certainly an important point, but on the other hand the facility with which the slides can be exhibited both before and after the lecture in properly constructed frames, when they can be copied, and the ease with which rough photographic copies can be made from the original negatives from which the slides were prepared, in my mind carries with them a distinct advantage. If the lantern-slides are prepared in the school or college where the lectures are delivered, copies of tlhe more important ones can be made upon paper, and be distributed with very little trouble and at a very small cost. These can be gummed into the note-books of the students, and will act as lasting records of the chief points of the lectures. In order to show clearly the advantages which lantern-slides possess over diagrams, I cannot do better than place lists of their re = spective qualities side by side :— VETSU3 LANTERN-SLIDES Cost at a small cost, when negatives ' have once been secured. ... Storage i Take up very little room, and cau easily be found when wanted Reproduction Can easily and quickly be repro duced by phctography Wear and tear Will keep clean ... Me ila Space required for | One screen of the size required exhibition Photography Direct photographs can be used Can be reproduced in any number, | last as long as a diagram if used with care, aad will always DIAGRAMS. Exceedingly expensive, Require great space and care; are ditficult to find. Must be copied by hand or printed : photography too expensive. Become of necessity very dirty if much used, and quickly get torn and injured. To be well seen must be large, a number taking up considerable space. : Copies must be made, at the sacrifice of truthfulness.