TETRAEEDRAL KITEb. 



139 



ful than this one have since been built and prove beyond a question 

 that a practical, efficient and powerful method of combination of small 

 forces has been discovered. 



Dr. Bell has been building during the past summer thousands of 

 tetrahedral cells varying in size from 35 cm. to 1 meter. Some of 

 them are covered with light red silk weighing about -iO grams to the 

 square meter and others with nainsook, very fine cotton, about as light 

 as the silk. Some of the earlier cells were covered with cheesecloth, 

 but the cheesecloth weighed so much — over 100 grams to the square 

 meter — that Dr. Bell has discarded it. The framework of the cells 

 is usually of black spruce, which is light and strong. 



To make a tetrahedral cell, take six sticks of equal length and 

 place three of them on a table so as to make an equilateral triangle. 

 Erect one of the three remaining sticks at each corner of the triangle 

 and bring the tops together. It 

 is the old-fashioned puzzle of 

 making four triangles with six 

 matches. Then cover any two 

 sides and you have a tetrahedral 

 winged cell. 



A number of cells outlined 

 against the sky look like a flock 

 of birds; for instance look at 

 Fig. 18; the wings of a cell are 

 also like a bird's wings in that 

 they are not rigid like a board; 

 the silk covering yields somewhat 

 to the pressure of the wind as the 

 feathers of a bird's wing. 



Hundreds of tetrahedral cells 

 are now being made in which the 

 frame consists of hollow alumi- 

 num tubing. The aluminum 

 weighs very little more than the 

 spruce wood hitherto employed 

 and gives much greater strength 

 to the frame. 



Using these cells just as a 

 mason uses bricks to build houses 

 of many forms, he has been con- 

 structing kites of every shape that a fertile brain could devise. Steadi- 

 ness in the air and lifting power have been the main object in all. 

 Some of his combinations are gigantic, exceeding twenty-five feet in 

 length and twelve and fifteen feet in height and width, but in spite 



Fig. 7. 'Red Flier' in the Air. 



