Global Hydromagnetic Wave Ducts in the Exosphere

IN 1957, one of us (H.A.B.) considered the initiation of an earth-magnetic field experiment to detect hydromagnetic waves in the upper ionosphere and exosphere. He suggested the use of very large wire loops (of about 100 km. 2 area) as pick-up systems for earth-magnetic field perturbations. A large loop has the advantage of a very high signal-to-noise ratio, since it effectively averages out local magnetic interference.