Page:Popular Science Monthly Volume 64.djvu/135

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I HAVE been asked by the editor of The Popular Science Monthly to write an article for that journal describing the tetrahedral kites of Dr. Alexander Graham Bell. I am glad to comply with his request, especially as I have had the good fortune for several summers past to watch the marvelous kites which Dr. Bell has been building in his laboratory at beautiful Baddeck, Nova Scotia. In this brief article there is not space to describe all the experiments that have been made, and I shall endeavor to explain, therefore, only the more important principles that I have seen evolved.

Dr. Bell began building kites in 1899. He was led to experiment with them because of his interest in the flying machine problem and his belief that a successful kite will also make a successful flying machine. A kite that will support a man and an engine in a ten-mile breeze will probably also support the man and engine when driven by a motor at the rate of ten miles an hour. This proposition has not been actually proved, but there can be little doubt that it makes no difference whether the kite is supported by the motion of the air against it or by its own motion against the air.

In a calm a kite rises when it is pulled by a man or horse, because of its motion through the air; there is no reason to believe that it would not also rise when urged through the air by propellers. A kite then can be changed to a flying machine by hanging a motor and propellers to it and dropping the string which attaches the kite to the ground.

The first kites that Dr. Bell built for his experiments were of the Hargrave box type, which had been the standard kite since its invention by Mr. Laurence Hargrave, of Australia, in 1892. Small Hargrave box kites flew very well, but their flying ability became poorer as their size was increased; a gigantic Hargrave with two cells as big as a small room would not sustain itself in the air, and experiments showed that only a hurricane could make it fly. To obtain much lifting power with box kites it was necessary to send up a number of

  1. This article and the illustrations are protected by copyright. The copyright of the first three diagrams and the first four pictures is in the name of the National Geographic Society and the remaining pictures in the name of Gilbert H. Grosvenor.