The Biefeld–Brown effect is an electrical phenomenon, first noticed by inventor Thomas Townsend Brown in the 1920s, where high voltage applied to the electrodes of an asymmetric capacitor causes a net propulsive force toward the smaller electrode. Brown believed effect was an anti-gravity force, and referred to as " electrogravitics " based on it being an electricity/gravity phenomenon. It has since been determined that force is due to ionic wind that transfers its momentum to surrounding neutral particles.