SCOTT, STURNER and WILLIAMSON observed that a polyatomic gas exerts a torque on a heated cylinder if a homogeneous magnetic field parallel to the axis is present. This effect is explained, for high enough pressure, by the kinetic theory of polyatomic gases. Decisive is the huge “amplification of spin” occurring when spin is transferred from molecules to cylinder in “cut tennis ball reflexion”. Phenomenologically this is manifested in the boundary condition (4): the gas shall have a slip velocity, tangential to the wall, which is proportional to the tangential component of its “azimuthal polarization”.