During the years 1883-1886 different launches here were driven by aërial propellers or revolving sails, and the intention was a simultaneous utilisation of wind and steam power, nearly 80 per cent, of the wind directions being utilised, when sailing in a circular course. It was found that the efficiency of an aërial propeller, when correctly constructed, is a trifle superior (on account of the elasticity of the air) to that of a water propeller; at present, therefore, where the aerial propeller has come into practical use for driving aeroplanes its theory may perhaps attract attention.