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wpe2.jpg (40983 bytes) SM014      Magic Lantern     circa 1930     Light

  This is an apparatus, which enables a magnified image of small objects to be projected on to a white screen in a dark room.   In 1634 the Englishman John Bate gave details of such a device.   Michael Faraday reinvented it in 1836.   A typical form is called a Sciopticon.   The source of light, usually a petroleum-burning lamp with flat wicks is enclosed in a box having a chimney to provide a draught.   The box contains a concave mirror that redirects light going to the rear thus reinforcing the front beam, while two plano-convex condensing lenses concentrate the light on to the transparent object to be projected.   Two achromatic doublets spaced in a lens-tube comprise the image-forming optics, which can be moved bodily for rough focusing and with a screw adjustment for fine focusing.  

The Magic Lantern can project on to the screen physical experiments such as the expansion of liquid in a thermometer and the deflection of the gold-leaf electroscope.   If necessary, the inverted image can be righted by means of a right-angled prism in front of the lens tube.

The magnifying power of the Magic Lantern is calculated by dividing the distance of the lens from the image by its distance from the object.  So, large magnifications are possible by using a lens of short focal length.