The Optical Magic Lantern Journal (February 1892)

‘The Optioal Magic Lantern Journal and Photographic Enlarger. 19 box, it can be moved upwards, so as to permit | { the beam to pass horizontally through the con, densing lens seen in the front of the box, and | then through the: objective, seen on the extreme right of the figure. Some pieces of experimental apparatus require, from their nature, to be placed horizontally, and others vertically. Apparatus of the former kind | is placed on the top of the box, whereas apparatus which requires to stand vertically is placed in front, and the hinged mirror can be instantly altered in position to exhibit either, ‘at will, on the same screen. This lantern can be uscd for the exhibition of slides in the ordinary way, or the slides may be simply placed in a frame, laid upon the con densing lens on the top of the box. The latter arrangement has the great advantage that, if the lecturer, facing his audience, stands in front of the lantern and has the screen behind him, he sees the illuminated lantern slide right way up, so that he can read any printing or reference letters upon it, and can point with a pencil or needle to any portion of the slide. The awkwardness of the lecturer requiring to turn: his back upon his audience and use a large | pointer is thus obviated, and he is ready at any moment to substitute one illustration for another. Further, the upper surface of the slide being unobstructed, a square of finely-ground glass, rendered transparent by paraffin or other oil, may | be placed in the lantern, and, using a hard pencil, sketches or writing can be produced on: the screen before the audience, and any portion of the writing or sketching is readily rubbed out by means of a pad moistened with paraffin. In this way all the advantages of the blackboard, in facilitating the development of illustrations before the class, are obtained; and besides, when the screen has been filled the matter need not be rubbed out, but may be laid aside, to be again exhibited at any time. Diagrams -may, ‘of course, be rapidly prepared before a lecture, and any portions may be omitted and supplied before the audience. Square and compasses can be readily used in the lantern, Admirable lantern slides can be produced upon clear glass by means of a pen and stencil ink, and the ink can also be used for making temporary adi!tions to ordinary photographed slides by sketching upon the cover glass. The principal source of lantern stides, however, will usually be illustrations taken from books, periodicals, or natural objects reproduced by photography. ( [4 he continued.) 10: Pressure Gauges for High-Pressure Gases.* By C. F. Bunensure. Tue frequent recurrence of late of more or less violent explosions connected with the use of pressure sa gauges on oxygen cylinders appears \ to have created much uneasiness, and even alarm, in the minds of all interested in the application of these cylinders for lantern work. In consequence. pressure gauges in general have becn emphatically condemned; and even upon the best authorities, lanternistsare strongly advised to discontinuc | their use entirely. The great utility of these gauges in ' enabling the manipulator to readily ascertain the exact quantity of gas cortained in a cylinder is, however, universally acknowledged ; and, before urging the discontinuance of their use, careful inquiries should surely be made to ascertain what has been the precise cause of these accidents, and whether means cannot be found or devised for preventing them in the future. In claiming this amount of consideration on behalf of these instruments, I would plead that, so far as my experience goes, these accidents invariably admit of a simple explanation, and are the result of either gross carelessness or ignorance on the part of the maker or operator. , All thatis required is that lanternists shculd assure : themselves that the gauges they use are properly made and fitted for the particular purpose upon the principles which are now fortunately well understood ; and, if this were universally done, I have little hesitation in prophe‘ sying that nothing more will be heard of these explosions —at any rate in connection with pressure gauges. It is the special object of this paper todraw your attention to the neceseary safeguarcs; but, before entering upon a consi@eration of these explusicns themsclves, it will te *\ Communication to the Lantern Society,