The principle of this invention consists in giving lateral motion to balloons by utilizing the resistance of the air, during successive ascents and descents, by means of a large triangular sail, placed between the bag and the car at an oblique angle with the horizon; and in rotating them at will by means of a smaller rudder–sail, which is capable of turning on a horizontal axis. The sails are constructed to furl readily.

The principle was first applied to a buoy, depressed to the bottom of a running stream. As it rose it could be made to turn in either direction, according to the setting of the rudder, and would proceed in a course opposed to the stream if thus directed, and all by passive means. When weighted it would act similarly during descent. On removal of the weight, it would continue its course whilst re–ascending, and so on. Anyone can experiment for himself, at a trifling cost, in this way.