Abstract: Apparatus for determining the speed and direction of a moving medium such as the atmosphere. The apparatus includes a sensing element which is exposed to the wind to be subjected to forces which displace the sensing element from its rest position. Attached to the sensing element is a dielectric slab which moves in an electric field. The sensing element resides in an equilibrium position determined by the forces applied by the moving medium and those applied by an electric field between the dielectric slab and a set of conductive plates. The displacement of the sensing element is variously determined to indicate the speed and direction of the wind.