In the case of wind pressure on a sloping roof surface, R is the
horizontal and L the vertical component of the normal pressure.
In experiments with the whirling machine it is the resistance to
motion, R, which is directly measured. Let P be the pressure on a
plane moved normally through a fluid. Then, for the same plane
inclined at an angle [phi] to its direction of motion, the resistance
was found by Hutton to be
R = P(sin [phi])^{1.842 cos [phi]}.