Magic lantern slide: Venice, Gondola effect

Magic lantern slipping slide: Venice, Gondola effect (bottom lantern).

A slipping (or slipper) slide is designed to give movement to a still drawing to reveal something which was previously hidden. There are two main types of slipping slide, single and double. With the single slide, the action is produced by sliding one glass in front of another. - two glasses are mounted in a wooden frame, one of which is fixed and the other moves across it. The movable glass is called the slipping glass and can be moved usually into two final positions to mask off then reveal part of the image.