"Early in 1879 Reynolds submitted a paper to the Royal Society in which
he considered what he called "thermal transpiration", and also discussed
the theory of the radiometer. By "thermal transpiration", Reynolds
meant the flow of gas through porous plates caused by a temperature
difference on the two sides of the plates. If the gas is initially at
the same pressure on the two sides, it flows from the colder to the
hotter side, resulting in a higher pressure on the hotter side if the
plates cannot move. Equilibrium is reached when the ratio of pressures
on either side is the square root of the ratio of absolute
temperatures. This counter intuitive result is due to tangential forces
between the gas molecules and the sides of the narrow pores in the
plates. ...
The vanes of a radiometer are not porous. To explain the radiometer,
therefore, one must focus attention not on the faces of the vanes, but
on their edges. The faster molecules from the warmer side strike the
edges obliquely and impart a higher force than the colder molecules....
The net movement of the vane due to the tangential forces around the
edges is away from the warmer gas and towards the cooler gas, with the
gas passing around the edge in the opposite direction. The behavior is
just as if there were a greater force on the blackened side of the vane
(which as Maxwell showed is not the case); but the explanation must be
in terms of what happens not at the faces of the vanes, but near their
edges.
Maxwell refereed Reynolds' paper, and so became aware of his
suggestion. Maxwell at once made a detailed mathematical analysis of
the problem, and submitted his own paper, "On stresses in rarefied gases
arising from inequalities of temperature", for publication in the
Philosophical Transactions; it appeared in 1879, shortly before his
death. The paper gave due credit to Reynolds' suggestion that the
effect is at the edges of the vanes, but criticized Reynolds'
mathematical treatment. Reynolds' paper had not yet appeared (it was
published in 1881), and Reynolds was incensed by the fact that Maxwell's
paper had not only appeared first, but had criticized his unpublished
work! "