Crooke's Otheoscope

This demo is a rare alternate version of the famous Crooke's Radiometer.Historically, Crooke's created a number of radiometer designs, with the "light mill" version being the most popular.

This demo is particularly interesting, as it directly disproves the "radiation pressure" description that is given for the radiometer - that the light is somehow "pushing" on the blades of a radiometer.

In this setup, the blackened/reflective elements are not hooked up to a rotating disk,they are completely isolated from it. The disc passes through a slot in the metal
no "light pressure" on the vertical blackened plate can explain the rotation of the disk.

A more plausible explanation of the inner workings of this demo is through the notionof "thermal creep".

See the following PDF document for more details:

http://www.physics.utoronto.ca/~salbarou/pub/DemoDocs/The%20Otheoscope.pdf

A special thanks goes out to D. Paige Wilson for her extensive investigation into the history and inner-workings of this apparatus.