An electromagnetic perpetuum mobile?
  A charge moving freely in orbit around the Earth radiates according to Larmor's formula. If the path is closed, it would constitute a perpetuum mobile. The solution to this energy paradox is found in an article by C. M. DeWitt and B. DeWitt from 1964. The main point is that the equation of motion of a radiating charge is modified in curved spacetime. In the present article we explain the physics behind this modification, and use the generalized equation to solve the perpetuum mobile paradox. 
{\O}yvind Gr{\o}n and Sigurd Kirkevold N{\ae}ss