The toy is called a Radiometer and the effect is the
"radiometric effect". You can see a picture of one at:
http://store.yahoo.com/explo/radiometer.html

The rest is some notes I made about URLs I found with google.

- Vince

http://www.globalwarmingsolutions.co...otheoscope.htm
several orders of magnitude greater than solar sail force
10E-3 to 10E-4 atmospheres

"Reynolds and Maxwell proposed an explanation involving
'thermal transpiration' but even today there is still no complete
explanation of how this little toy works."

"There has been no attempt to harness the rotational energy to
measure the efficiency of conversion but I suspect that solar
is converted into rotational energy with very high efficiency
in the radiometer."

http://www.betrisey.ch/presbok11.htm
"The mechanism by which it operates is very complex and
frequently stated incorrectly."
Experiments seem to indicate "thermal transpiration" is at least
most of what is going on.

http://students.cec.wustl.edu/~sapph...adiometer.html
AMSAT people used radiometric effect to induce 1/2 rpm in 3 weeks
time

http://eotvos.dm.unipi.it/nobili/ope...r_PRD_2001.pdf
Left side of page 2 has formula for "radiometric effect" given
temp, pressure, ...

http://eotvos.dm.unipi.it/nobili/ope...pe_revised.pdf
Has formula

http://science.howstuffworks.com/question239.htm
Crookes' radiometer

http://math.ucr.edu/home/baez/physic...ight-mill.html
Thermal transpiration / light-mill
Thrust comes at the edges - discounts many other explanations

http://sargentwelch.com/product.asp?pn=WL1734%5FEA
$10 - 99% evacuated - gas expands on black side and so pushes
This looks like the one I have

http://scientificsonline.com/product.asp_Q_pn_E_3116000
Hand made radiometers.
"Energy is released as the heated molecules kick away at great
speeds, causing the vanes to revolve within the vacuum."