Rackwork polarising magic lantern slide
- c. 1880
Rackwork polarising magic lantern slide with hand crank and brass rod control with rotating coloured glass polarising discs which change the image from purples to greens and vice versa.
In a rackwork slide one glass disc revolves in front of another. The moveable glass is mounted in a brass collar with a series of vertical teeth around its upper edge, forming a rackwork rim. A steel pinion with a matching toothed-end engages the rackwork and a handle is fixed to its other extremity. On turning the handle the rackwork is driven round by the pinion causing the glass to rotate.