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The Magic Lantern

Of all optical instruments, the magic lantern deservedly holds the first place in popular estimation. Formerly it was looked upon merely as an amusing toy, but latterly, and more especially since the use of photographs on glass has superseded the old hand-painted slides, its importance as an educational help has been universally recognised.

The toy lantern consists of a tin box with a hole in front for the admission of a bull's-eye glass called the condenser. This concentrates the light from an oil lamp upon the painted slide, the image of which is afterwards magnified by another lens called the object glass, and that enlarged image is depicted upon a wall or screen. The toy lantern is so well known that it needs no further description, and the annexed cuts of the instrument, and the kind of pictures usually supplied with it, will sufficiently show its character. Had this crude form of lantern not been much improved, it would certainly have remained where it ought to be, in the nursery. But gradually opticians have so altered it that the modern magic lantern represents a most perfect instrument, and one which is constantly called into requisition for illustration by the first scientific lecturers of the day. It is a pity that no one has yet found a better name for it; its old appellation still sticks to it, and seems likely to do so.

The essentials of a good magic lantern are good lenses and a good light. The use of the condensing lens can be easily understood from the annexed diagram, where A is the condenser (usually formed of two plano-convex glasses placed face to face as shown); B, the slide or picture upon which its beams are concentrated, and C, the object glass which magnifies the image. The dotted lines show how the rays of light would be scattered and lost in the absence of the condensing lens, which bends them on to the picture. A capital object glass is represented by a quarter-plate lens such as is used for taking photographs. Such a lens of foreign make can often be picked up for a few shillings, and the buyer of one will have the satisfaction of considering that his purchase will serve both purposes. With such a lens, and a condensing lens, fitted into a mahogany box with a tin top and chimney, a very respectable lantern can be made at home. The next important point is the form of lamp. The oil lamp is no use at all, unless it be of some modern form such as the Silber burner. This, or an adaptation of it, can also be used with ordinary house gas. Paraffine is better still, and the lime light may be said to be perfection itself.

The introduction of special paraffine lamps forms a new era in the history of the lantern. Some are sold with double and some with triple wicks, and the light is so bright that they will give a well illuminated six-foot disc. This is of course quite sufficient for private purposes. A lantern of this type, made by Mr. Browning, is shown in the annexed cut. It may be remarked that there is no danger in using good paraffine oil. The lamp is so arranged that it cannot get over-heated, and, if carefully trimmed and kept clean, there is no unpleasant smell from it. With such a lantern as this, and a small stock of good photographic transparencies, a very delightful evening's entertainment may be arranged. Series of photographs with suitable readings can be hired of many opticians, and by adopting this system a constant variety is obtainable.