In some of my last essays i asked about an experiment i have seen in TV in
germany. A american group of scientists presentet the spinnimg of a black
wheel while radiation incident perpendicurar on the wheel.
The wheel was sensitively mounted in a evacuatet glass tube. It was around
1991 or 92.

I do not know the origin, but i want to say that this was a great
experiment.

It leads to a flux density which is electromagnetic origin. Except the
energy flux density there exists another flux density in electrodynamics, i
call it spin flux density. It has the direction of the energy flux. It
differs by a factor 1/frequency from the energy flux density and it is built
up by the difference of the circular split of a elliptic polarized wave.
Note the energy density is the sum (not the difference) of both.

This simple formula i found 1992 cause i was concerned with polarization
calculations. I found the following rules that time:
1. The energy is propotional to the square of the two main axes of the
ellipse. while the spin flux is proportional to the product of both.
2. 2002 i found that this flux density fulfills a conservation law for the
normal component when you have a incident wave on a non absorptive
macroscopic medium. Formulas similar to the Fresnel formulas. The reflection
coefficient for example is the square of the product of the reflection
coefficients for the perpendicular and parallel polarized part of the
incident wave. The transmission coefficient is the square of the product of
the Fresnel transmission coefficients times a simple factor. Reflection plus
transmission coefficient equal 1 for these spin fluxes.
3. Linear polarized waves do not transport spin.
4. The flux is proportiobal to the vector product of E and E*, the complex
conjungated field. If you assume
the electric field to be real, this flux would not exist, because the vector
product of the same real vector is zero !
5. Thermal light - circular or elliptic polararized - which comes directly
from a thermal source like a lamp or the sun - does not show spinning of the
wheel.

This symmetry i call the spin symmetry of classical electrodynamics. There
exists a variety of possibilities
to form spinwaves from thermally emitted waves:
1. Using a circular polarizer to strip of one of the two rotating fields in
a thermal emitted wave (the rotation for both goes in opposite direction)
2. Linear polarize thermal emitted wave and then make a metal or total
reflecion (then you get light which is elliptic polarized and having spin
3. I also found a literature note that thin magnetic layers on a substrate
could have such an effect.

I also thought upon thermodynamic machines an found following rules
1. You can not find polarizers in nature with can polarize thermal light
linear or circular with more than 50% efficiency. Normally very much less
than 50 % efficiency.
2. Energy which is transferred in form of a momentum to the body (the
rotating black wheel) can not be transformed to thermal energy at the same
time.
3. There are frequency dependent effects which limit radiation machines to
efficiencies not far away from the efficiencies of solar cells.

Spin effects can be used to directly transform radiation energy to
mechanical energy.