  It has been established that the Rieger periodicity of approximately 153 days
is part of a complex of periodicities, all multiples of a basic period of
approximately 25.5 days. However, it has not been clear why the sixth
subharmonic of this periodicity should be preferentially manifested. We here
note that if the Sun contains two rotating elements, with different periods and
different axes, a special situation will arise if the two periods have a lowest
common multiple, for in this case the relative configuration of the two
rotators would repeat exactly at that (LCM) period. This chain of thought leads
us to suspect that the Sun contains a second rotating element with rotational
period in the range 21 - 22.5 days.
