The Optical Magic Lantern Journal (February 1893)

36 The Optical Magic Lantern Journal and Photographic Enlarger. that audience as a most appreciative one. When all was over I asked the Superintendent what he thought. Here, I said, 1 have given two short scientific lectures, shown over eighty scientific slides, and only six comic slides, which latter were not appreciated. Now this is a lesson that might be carried away in hundreds of cases. Science need not be dry, nor uninteresting, nor difficult so understand. On the contrary it could, by aid of the lantern, be made a source of endless entertainment and instruction, and the lantern when properly censtructed, lends itself to almost every branch of science. By it experiments and demonstrations to our friends at home may be conducted with far less expenditure in apparatus and material than by any other method, It would be out of the scope of the present communication to enumerate the home experimeuts that may be performed even with an oil-burning lantern and a few accessories that are easily made or purchased for a few shillings. ‘‘ BOOKS ON OPTICAL PROJECTION. “But, How to begin? Well, there are plenty of books published on the subject of optical projection, and a new one, just published, Sunshine, by Amy Johnson, L.L.A., F.R.AS., is a delightful lantern book, comprising a series of about forty popular experimental lectures on science delivered to young people, with special considerations for optical projections. Indeed, there is a section of the book devoted to lantern projection, with practical hints and home experiments. Another charming little book is Soap Bubbles and the Forces which Mould them, by Professer C. V. Boys, F.R.S. This book also contains a section of practical hints to the lanternist for making and projecting those interesting and fascinating playthings of our boyhood, soap bubbles. The author also describes other experiments, ‘so wonderful and yet so simple that, if they had been performed a few hunderd years ago, the rash person who showed them might have run a serious risk of being burnt alive.’ Lastly, Science at Home, a pamphlet by the late W. B. Woodbury, is recommended as containing a number of beautiful lantern experiments,.all of which may be easily performed in our own family circles by the merest tyro. ‘(THE LANTERN ITSELF. ‘« Respecting the lantern itself, much might be said in favour of lime-light, though for home use “a good oil Jamp—one that does not smell or burn like a roaring furnace—is very convenient, and answers most purposes if the screen be not too large. A good opaque screen, about four feet six Inches square, was generally large enough for home use with an oil lamp; but in a large room—still using the oil lamp—a translucent screen of about the same size would be better; and it might be worth while to mention that only a few days ago a most successful exhibition was given to an audience of over 200 people on such a screen—three feet six inches square— with an oil lamp, and it will be seen that had the pictures been projected to seven feet by the same luminant, the illumination would only have been one-fourth, because seven feet square is four times the area of three feet sixinches. By using compressed oxygen in cylinders, as now supplied commercially, there is practically no danger in using the Innelight, and it may truly be said to be safe, or safer, than a paraffin lamp.” VARIOUS EXPERIMENTS. Mr. Chadwick then proceeded to exhibit a number of experiments. A wire stand was made to support a thin metal plate in a horizontal position (edgeways to the condenser), and under it was placed a spirit lamp. In a few seconds the plate becaine quite hot, and then a single drop of water was allowed to fall on upon the hot plate. The drop of water at once assumed the spheroidal form, and on the screen it could be seen separated froin the plate by a film of vapour. The spirit lamp was now removed, and as the plate cooled the drop of water burst into steam and was gone. This beautiful experiment illustrated a frequent cause of steam boiler explosions. From suddenly letting off steam the water in the boiler assumes the spheroidal form, and a thin film separates the water from the boiler, which later rapidly heats. The engine-driver or the fireman, thinking his water is getting low, pumps in cold water. He thus cools the boiler, destroys the spheroidal form, and the accumulated heat, suddenly converted into steam, bursts the boiler. A long focus lens is best for showing this experiment. The same experiment is often scen in the kitchen, when cold water is put into a hot frying-pan, and the water runs about in “blobs.”” This was followed by experiments illustrating the retention of images on the retina by pieces of perforated card placed in the lantern. White spots were seen on a dark screen. After a minute the light from the lantern was shut off, and the screen dimly lighted from a gas bracket in the room. The audience saw the spots now reversed and and quite black on a white screen. When a photographic negative of a portrait was projected on the white screen and looked at for a minute, the portrait was not always recognisable, but directly the light was shut off the image was “seen” as a positive and at once recognised, as someone said, ‘‘ You see it when you don’t see it, and then you do.’”” A number of experiments