TETRAHEDRAL KITES. 131 



THE TETRAHEDKAL KITES OF DE. ALEXANDER 



GRAHAM BELL.* 



By gilbert h. grosvexor, 



EDITOR OF THE NATIONAL GEOGRAPHIC MAGAZINE. 



I HAVE been asked by the editor of The Popular Science 

 MoxTHLY to write an article for that journal describing the tetra- 

 hedral kites of Dr. Alexander Graham Bell. I am glad to comply with 

 his request, especially as I have had the good fortune for several sum- 

 mers 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 ihotion 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 inven- 

 tion by Mr. Laurence Hargrave, of Australia, in 1892. Small Har- 

 grave 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 



* This article and the illustrations are protected by copyright. The copy- 

 right 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. 



