Page:Popular Science Monthly Volume 64.djvu/142

138 Fourth.—By the use of the tetrahedral cell it is possible to build kites unlimited in size and in which, however gigantic the kite, the ratio of supporting surface to weight remains the same as in a small kite.

The successive doubling in size of the kite shown in Fig. 3 may be carried on indefinitely without the weight increasing faster than the wing surface. The cells all act in harmony; no part of a kite built of tetrahedral cells has to be strengthened to counterbalance an opposing force or a weakness in some other part of the kite; no weight is thrown away.

By his invention of the regular tetrahedral winged cell, Dr. Bell thus got around the old law which said you can build kites up to a

certain size, but no greater. The adherents of that law have always admitted that the law might be circumvented if a kite could be combined of many small models, but they have denied or at least doubted that a working combination of small models effective enough to carry a man, and to be called a flying machine, could be made. With his tetrahedral cell Dr. Bell has, however, been able to build kites of tremendous power, strong enough to carry up several men. One of his first kites lifted two men off their feet in a squall, and they only saved themselves from an undesirable ascent by instantly dropping the rope. Later this same kite (Fig. 4) snapped its rope, a three-eighth-inch new manila rope, as quickly as a thread. Kites much more