Tape backup / Bizzare Device Question

[David Scheidt]

On Tue, Mar 07, 2006 at 02:09:40PM -0000, Graham Bentley wrote:
> 
> Description: Glass bulb, similar to light bulb but with 
> narrow end flared at bootom so it standsup. Inside, 
> a rotating wire device that has 4 squares of card like 
> material attached, like vanes. 
> 
> One one side they are black on the other they are white. 
> When the sun shines brightly enough, the white side reflects 
> the light energy and the black side absorbs it. The vanes 
> spin around. 
> 
> This does exist and has a name and I know there are 
> some very knowledgeable people on this list who will 
> know.

It's called a radiometer.  I've seen them called other things, like a
"lightmill" or a "light gauge".