Aeronautics now covers a large field. The bibliography alone, compiled and published annually by the United States National Advisory Committee for Aeronautics, requires something like two hundred pages of a book seven inches by ten inches. Needless to say, I am not undertaking to review the whole field.

Owing to the difficulties of conducting free flight tests of performance and the fact that we cannot afford to make many mistakes in an appliance whose operation involves the risk of human life, it is peculiarly desirable that we may be able to predict the performance of the completed airplane from small-scale experiments; and probably in no other branch of mechanical science have we at present so many research laboratories.