much imagination to picture how impossible it would be for the aviator to make his voice heard in a transmitter alongside a 200 horse-power airplane engine. But a brilliant series of experiments, conducted largely by Mr. J. P. Minton, of the Western Electric Company, resulted in a form of telephone-transmitter or microphone which possessed the remarkable quality of being insensible to engine and wind noises and at the same time highly responsive to the tones of the voice. With these two elements in hand it was thought that the problem was solved, but three more months of unremitting work were required to perfect the apparatus to a state where it was practicable for use by others than experts. At last everything was ready, however, and in December, 1917, the officials of the Aircraft Production Board and the joint Army and Navy Technical Boards announced that they would witness an exhibition of the apparatus at the Moraine Flying-Field at Dayton. Two days before the date set for the demonstration a group of the engineers and mechanics who had been working over the problem almost night and day during the preceding six months descended, with many cases of paraphernalia, on the Ohio town. Only the enthusiasts who for the preceding half-year had spent their days working over the problem and their nights dreaming of it believed that the exhibition would prove successful. Every one else was sceptical. The plan was to have two planes, both carrying radio sets, in the air at the same time, while the visiting officials listened in at a ground-station located on the top of a near-by hill. That night the inventors and their assistants congregated in a room of the hotel where they were staying and worked out a scenario and held a rehearsal of the morrow’s programme. A famous electrical expert represented one plane and a young engineer represented the other, while the inventors, sitting in the middle of the room, gave them their orders and sent them sailing over beds, chairs, and tables as it was hoped their planes would manœuvre in the clouds the next day. No one slept very well that night. The morning was cold and dismal, in keeping with the spirits of all concerned. Upon the arrival of the exalted ones, among whom were several of the foremost scientists and inventors of America, they were shown the apparatus installed in the two planes and were told what it was expected to do. They were then escorted up to the little station on the hill, where a loud-speaking receiver had been connected with the wireless apparatus, so that all could hear without the use of head-sets. The planes left the ground, and after what seemed an interminable length of time, there came from the receiver the first faint sounds which indicated that they were ready to perform. The officials, with their coat-collars about their ears, appeared only mildly interested and several gave unmistakable signs of being bored. Suddenly,