This paper contains an explanation for phenomena found in laboratory plasmas by many investigators. When a magnetic field is present, either the ion component or the electron component (but not both simultaneously) may rotate with a mean angular velocity equal to its cyclotron frequency. In such a case, the periodic electric and magnetic force fields induced by certain types of collective oscillations of the velocity field cooperate in such a way that rotating wave patterns are formed. These rotating waves fall into two groups. The frequency of the first group is the well-known plasma frequency. The second group has two frequencies—one near a multiple of the cyclotron frequency, and the other, much lower, at the square of the plasma frequency divided by a multiple of the cyclotron frequency. The field of motion of the first group of waves is periodic along the direction of the magnetic field. The field of motion for the second group of waves is given by where and These fields of motion are in agreement with the experiments which have found that the higher harmonics of the cyclotron frequency can be excited to a much higher degree than previous theory had predicted.