MAGIC LANTERN is a species of lucemal microscope, its object being to obtain an enlarged representation of figures, on a screen in a darkened room, by means of the pencils of light issuing from a lamp or candle and through a convex lens.
The instrument consists of a lantern, generally of tin, and of a cubical form, in the interior of which is the light ; and at a perforation in one of the sides is applied a tube projecting horizontally from it. Immediately before the aperture, and within the tube, is a glass lens, often nearly a hemisphere and three or four inches in diameter, serving to condense the light which proceeds from the lamp both directly and by reflexion from a concave mirror attached to the side of the lantern which is directly opposite the aperture : this tube carries within it another, which is also provided with a convex lens, and is capable of a small movement for the purpose of adjustment.
A groove in front of the lantern and parallel to that front receives a rectangular frame containing the glass plates on which are painted, with transparent colours, the objects of which an enlarged view is to be obtained. Instead of a single convex lens, the sliding tube is some times provided with two such lenses ; these are placed at a short distance from one another, and have between them a perforated plate of tin, or diaphragm, crossing the interior of the tube, for the purpose of cutting off the more divergent rays which would render the figures indistinct. The lens, or pair of lenses, is of such a focal length that the rays in each of the pencils which proceed from the object may unite on the screen in what is called the conjugate focus, and thus produce the enlarged representation of the figure.
Several figures are usually drawn on the same plate of glass, and the plate is capable of being moved by hand in the groove so that the different figures may be brought successively before the spectator : for the purpose of heightening the effect, motions can be given to the figures by means of a simple wheel-work.
The magic lantern is said to have been invented by Kircher, In the 17th century • it is described by him in his 'Ars Magna Lucia et Umbrx.' Cellini, however, who died in 1570, describes some magical effects, such as spectres in the midst of ascending smoke, &e., which are easily produced by the magic lantern, so that Kircher, who was not born until the year 1601, was but a re-inventor, or perhaps only a describer of an instrument, the possessors of which would be likely to keep it secret 88 far as possible. The celebrated Euler proposed to
substitute for the lens of the lantern a concave mirror, perforated in the middle like that of a Gregorian telescope : this was to be placed in the interior of the lantern with its polished surface towards the light and its convexity towards the object. The light was to be so disposed that none of it should pass directly through the aperture in front of the lantern so as to fall on the screen; and that which was reflected from the concave mirror, after falling upon one with a plane surface, was from thence to be reflected in a contrary direction upon the object. The rays in the pencils proceeding from the object were to pass through a lens in the tube, as in the former construction ; and, by converging with greater accuracy to points on the screen, they would have pro duced a more correct image than that which results from refracted light alone.
The magic lantern must have been at best an imperfect affair until the invention of the Argand lamp, by Ami Argand in 1789, by which a clean, clear, bright flame was for the first time produced in lamps. It was not, however, until 1802, that any decided improvement was made, and then M. Philipsthal exhibited at the Lyceum in London the form of instrument known as the Phantasmagoria. The lantern itself was similar to but larger than that which served for more general purposes ; and the sliding tube which carried the farthest lens had a greater range of motion. The objects to be exhibited were painted upon a glass plate, with this remarkable difference from former attempts, namely, that all the parts not occupied by the figure, were covered with an opaque varnish, so that no light could pass except through the figure, which was thus rendered more brilliant. The machine was placed upon a stage capable of being moved on wheels in a direction perpendicular to the screen on which the objects were represented. 'I he screen was a curtain made of fine muslin or gauze, and covered with varnish so es to be quite transparent : it was stretched in a vertical position across the theatre or apartment ; and this being made quite dark, the spectators occupied the space in front of the screen, while the apparatus was disposed on the opposite side.