Letter from Thomas Gold to Dr Donald Menzel, Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts `Concerning a heavy vibrator transmitting a frequency modulated soundwave into the ground, and receivers that have the appropriate phase sensitive circuits as made by the Continental Oil Company for commercial use. This sounds very close to their patent. Is still game to write an article about the Moon with him if he still wishes. Gold thinks on the whole he is gaining ground. Will send him another article shortly. 26 September 1974