The wind instability of radio-galaxy clouds

It is shown that, in the magnetospheric model of radio-galaxy clouds, the wind instability is characterized by a lower critical velocity than the Kelvin-Helmholtz instability, and that it is associated with the scale of the most rapidly growing surface waves. These features of the wind instability make it possible to determine the ratio of the plasma density in the cloud to the plasma density in the flow of intergalactic matter past the galaxy.