  We present an exact formula for the computation of the interference rate of
radiation in the case of two charges revolving with constant angular velocity
at opposite ends of a diameter in a fixed circle. The formula is valid for
arbitrary velocities of the charges, and can be easily studied by numerical
methods, even for velocities very close to the velocity of light. For
ultrarelativistic motion, the interference rate of radiation behaves as
$\ln(1-v^2/c^2)^{-1/2}$, which contrasts with the behavior $(1 - v^2/c^2)^{-2}$
for the rate of radiation for one charge in circular motion. This is the first
exact calculation for the interference rate of radiation of two relativistic
charges, and it is useful in connection with the old controversy about the
correctness of the Lorentz-Dirac equations of motion for more than one charge.
