The two men made their way across the crowded Fair Grounds until they came in front of the large Grand Stand. Here a crowd of several thousand people were jammed around a platform on which were a few men, and a table of instruments, the largest part of which were four huge phonograph-like horns that faced in four directions. They made their way through the crowd and had just climbed to the platform, when a voice issued from the horns. The words were: “Have just reached three thousand feet.” Looking upwards, Pemberton could see a speck circling above and rapidly growing smaller. It was the aeroplane winging its way ever higher and higher. He leaned over to the President, “How is it we can hear their voices and can not hear the roar of the motor? On the ground it was impossible to hear a voice because of the deafening roar of an aeroplane motor.” The President leaned over and tapped one of the men on the shoulder, who was tinkering with the instrument, and said, “Billy, tell Mr. Pemberton here about the wireless telephone--tell him why one can hear a voice from above and yet not hear the roar of the motors.” Billy dropped into a chair next to Pemberton and keeping one eye on the instrument, explained: “Kidwell and Dexter are using the same kind of wireless telephone instruments that our aviators in France had begun to use when the war ended, to communicate with each other and with headquarters. You know sound is vibration of the air and travels in waves and in a straight line unless turned aside by something. The aviator’s instrument is like a helmet and covers most of his head. The receivers are flat and lie over his ears. The outside sound is deadened by the padding in the helmet and it was found that it would be necessary for the padding to cover most of the lower jaw to kill the outside sound. The mouth-piece, the part they talk into, is fastened directly in front of the mouth. It is padded to stop the outside sound. Only a tube-like opening directly even with the person’s mouth is left unpadded. There are three or four small holes in the tube and when the person talks, his voice is thrown straight through the small openings and makes the instrument work while other sounds pass by as the waves do not get a straight entrance to the diaphragm.” “Both the receivers and the mouth-piece have wires running to a plug in the side of the aeroplane which connects with the batteries and instrument that send the wireless waves in all directions and reach us; they also catch any that we should send and transfer it to speech when it reaches the ears. Instead of the usual receiving instrument, we have hooked on a sound magnifier here, so that everybody can hear directly. Now the very--” “One mile up and everything is running fine.” The voice of one of the men from the speck above spoke from the horns. A cheer greeted the announcement. * * * * * “Who is doing the talking?” Pemberton asked.