This is one of the most pleasing of all optical instruments, and it
is used to produce enlarged pictures of objects, which being painted
on a glass in various colors are thrown upon a screen or white sheet
placed against the wall of a large room. It consists of a sort of tin
box, within which is a lamp, the light of which passes through a great
plano-convex lens fixed in the front. This strongly illuminates the
objects which are painted on the slides or slips of glass, and placed
before the lens in an inverted position, and the rays passing through
them and the lens fall on a sheet or other white surface, placed to
receive the image. The glasses on which the figures are drawn are
inverted, in order that the images of them may be erect.