(Astrophys. Space Sci.). It is characteristic of the radiation from a particle of mass m bearing a charge e moving with ultrarelativistic velocity βc in a magnetic field of induction B0 that the bulk of the emission is confined to a small cone of directions within O(ξ) of the direction of motion τ which makes a constant angle α with B0, and that for any direction n at an angle θ with B0 such emission is observed as harmonics of the fundamental frequency fB0ξ/a, where fB0 is the nonrelativistic cyclotron frequency and