Many contributions of value to the general theory and practice of training for flying were made by these enthusiastic young men who toiled unceasingly over the problems set by our training fields. One young lieutenant, while studying the causes of airplane accidents and trying to find some means of preventing them, worked out a series of exercises which reproduce the positions that must be taken in advanced flying and so enable the cadet early in his work to find out whether or not he is physically unfit to undertake acrobatic work and also give him a measure of preparation for it. Experiment showed that the motion picture film had possibilities for the flying instructor and when hostilities ended it had been drawn into the system of training and was beginning to be used to hasten and to make safer the cadet’s progress. Sitting safely in his chair, he watched whirling horizons, skies and landscapes, pictured from an airplane going through one acrobatic performance after another, noting the varying appearances of the pictures and his own sensations, and so having his nervous system educated in advance for what he would have to undergo, learning in time whether or not it would unduly affect him and gaining quickly and without danger valuable experience. An important development, worked out and used at American flying fields, was a series of tests of the flier’s physical ability to endure high altitudes. Observation showed that accidents sometimes were the result of inability to endure rarefied atmosphere and by placing the student in a tightly closed room, gradually exhausting the oxygen and noting his reactions it was speedily determined whether or not it was safe for him to attempt high flights, either with or without a device for supplying him with oxygen.