SCIENCE OF COMMON THINGS. 285 



Franklin's experiment with a kite. Identity of lightning and electricity. 



whole current to the earth, the lightning will fuse the 

 metal and enter the building. 



1861 By' whom was Uie identity of lightning and electricity first esta- 

 lliahed f 



By Dr. Franklin, at Philadelphia, in 1752. 



The manner in which this fact was demonstrated, was as follows: 

 Having made a kite of a large silk handkerchief stretched upon a frame, 

 and placed upon it a pointed iron wire connected with the string, he raised 

 it upon the approach of a thunder storm. A key was attached to the 

 lower end of the hempen string holding the kite, and to this one end of a 

 silk ribbon was tied, the other end being fastened to a post. The kite 

 was now insulated, and the experimenter for a considerable time awaited 

 the result with great solicitude. Finally, indications of electricity began 

 to appear on the string; and on Franklin presenting his knuckles to the 

 key, he raised an electric spark. The rain beginning to descend, wet the 

 string, increased its conducting power, and vivid sparks in great abun- 

 dance flashed from the key. 



18 63 Why was the Me insulated when FranUin fastened tlie key to the 

 post with a silk ribbon ? 



Because the silk was a non-conductor ', and would not 

 allow the electricity received upon the kite to pass off 

 by means of the string to the ground. 



1863 Was this experiment one of great danger and risk ? 



It was ; because the whole amount of electricity con- 

 tained in the thunder cloud was liable to pass from it, 

 by means of the string, to the earth, notwithstanding 

 the use of the silk insulator. 



1864 If a lightning rod is made of iron, how large should it be f 



Not less than three-quarters of an inch in diameter. 



1865 In what manner should the rod be erected ? 



The rod should be continuous from the top to the bot- 

 tom, and an entire metallic communication should exist 

 throughout its whole length. 



This law is violated when the joints of the several parts that form the 

 Conductor are imperfect and when the whole is loosely put together. 



1866 How should tlie conductor be fastened to tfie building? 



By wooden supports. 



- If there are masses of metal about the building, as gutters, pipes, etc., 

 these should be connected with the rod by strips of metal ; for unless this 

 is done the lightning may pass from the rod to the metal, and enter the 

 building^ 



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