The science of aerodynamics consists in the study of the phenomenon following upon the motion of a body through air, the object being to investigate the nature of the forces brought into action and to discover the reasons for these forces. We know from experience, for instance, that under certain conditions an aeroplane wing fails to exert sufficient lifting force to keep the aircraft in steady flight. From experiment it has been found that these conditions correspond to a breakdown in the flow of air over the upper surface of the wing,, and if we can discover some means of preventing this change we have, at least, served some useful purpose.