IF road locomotion remained impossible until the comparatively light petrol engine had been invented, the early motor was yet far too heavy, in proportion to its power, to make practicable locomotion in the air. Not until engineering progress had evolved the intemalcombustion engine with a weight for horse-power of less than three pounds did aeroplane design really begin. This evening Professor Burstall will describe the special problems involved in this, and the further difficulties of cooling an aero engine working at a tremendous speed.