Editing Crookes radiometer (section)

== Horizontal vane light mill ==
The thermal creep from the hot side of a vane to the cold side has been demonstrated in a mill with horizontal vanes that have a two-tone surface with a black half and a white half. This design is called a Hettner radiometer. This radiometer's angular speed was found to be limited by the behavior of the drag force due to the gas in the vessel more than by the behavior of the thermal creep force.  This design does not experience the Einstein effect because the faces are parallel to the temperature gradient.<ref>{{Cite journal|last1=Wolfe|first1=David|last2=Larraza|first2=Andres|year=2016|others=Alejandro Garcia|title=A Horizontal Vane Radiometer: Experiment, Theory, and Simulation|journal= Physics of Fluids|volume=28|issue=3|pages=037103|arxiv=1512.02590|doi=10.1063/1.4943543|bibcode=2016PhFl...28c7103W|s2cid=119235032}}</ref>