The wave motion of a revolving shaft, and a suggestion as to the angular momentum in a beam of circularly polarised light

When a shaft of circular section is revolving uniformly, and is transmitting power uniformly, a row of particles originally in a line parallel to the axis will lie in a spiral of constant pitch, and the position of the shaft at any instant may be described by the position of this spiral. Let us suppose that the power is transmitted from left to right, and that as viewed from the left the revolution is clockwise. Then the spiral is a left-handed screw. Let it be on the surface, and there make an angle є with the axis. Let the radius of the shaft be a , and let one turn of the spiral have length λ along the axis. We may term λ the wave-length of the spiral. We have tan є = 2 πa / λ . If the orientation of the section at the origin at time t is given by θ = 2 π N t , where N is the number of revolutions per second, the orientation of the section at x .