On the Rotation of the Planetary Nebulae

The angular momentum possessed by rotating planetary nebulae is greater than they could have possessed when their radii were small; it must have been acquired after they became large, or concurrently. It is shown that line absorption probably plays a much larger part than has hitherto been supposed, and that in that case the interac- tion of the Doppler effect due to spin with an Einstein red shift will darken the star's disk unsymmetrically, as seen by a nebular atom, and hence will give all such atoms a transverse component of momentum. The angular momentum thus acquired is suf- ficient to account for the observed velocities if the nebular mass is not more than about ten times that of the earth. The nebula and star rotate in opposite directions, but angular momentum is not conserved for the system considered apart from the stellar radiation emitted into space