Re: Light Mill?

[Doug Craigen <dcc@ESCAPE.CA>]

Spagna Jr., George wrote:
> Another "experiment" with the Crooke's radiometer (I think that's the
> correct name for the beast) is to place it near a (dare I say it?) heat
> source like a fireplace or open wood stove.  It will spin normally for a
> while, then stop.  Remove it from the vicinity of the fire, and it will
> begin spinning in the opposite direction.  Which supports the notion that
> its behavior has to do with the gas inside the bulb interacting differently
> with the light and dark sides of the vanes, rather than "radiation
> pressure."

You can get the same "unwinding" effect after removing it from sunlight
- but the reverse rotation is short lived.  In either case the
explanation for the reversal requires something not well known.
"Everybody" know that black heats up faster under illumination, but not
nearly as many people know that it also cools down faster when removed
from the illumination.

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Doug Craigen
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