133 IEEE TRANSACTIONS ON ANTENNAS AhTD PROPAGATION

Hershberger' raised the question of xvhether a multiplicit>. of resonances had been observed in radio reflections from meteor trails at frequencies near the plasma frequency similar to those observed from positive columns in the laboratory. Nolv that a theoretical description of the process leading to the laboratory observations is available2 one can determine whether such resonances might be observable. The theory requires a non-uniform distribution of electron density and it seems from experimental evidence that the appropriate boundary condition is zero space charge perturbation at the periphery of the plasma ~olumn.~ Thus i t may be tha t the dlffuseness of a meteor trail with electron number density varying as R =no esp ( -f/ro)2 causes an absence of subsidiary resonances. On the other hand the dispersion relation which gives rise to the waves