266 ELECTRICITY OF THE AIR j LIGHTNING. 



But Franklin showed, too, by direct experi- 

 ment, that thunder-clouds behave exactly as con- 

 ductors, which might be charged with electricity, 

 and insulated by the surrounding air — that is, cut 

 off from any electric communication with the 

 earth. He sent up a kite furnished with some 

 wire points, while a thunder-cloud was forming. 

 Thus, by means of the string, which, by being 

 moistened, became a carrier for the electricity, or 

 by means of a fine metal wire, which ran down 

 from the points, and was twisted into the string, 

 he succeeded in drawing down electricity from the 

 cloud, and in performing all the experiments for 

 which we usually resort to the aid of an electrical 

 machine. These experiments were afterwards 

 repeated and verified at many places. 



By this simple means — the electric kite — it has 

 been proved, that not only thunder-clouds, but all 

 clouds, are electrical, and that even the dry air 

 at all times contains electricity in great amount 

 but of very slight density. Many processes that 

 are going on upon the earth are possibly aiding to 

 maintain this condition, by generating electricity, 

 and giving it off to the air ; such as the rubbing 

 of the wind, and of evaporated water against 

 solid bodies, the burning of fuel, &c. What, 

 however, is to be considered as the main source 

 of the electricity of the air, is as yet by no means 

 clear. 



