FRANKLIN 1 S KITE EXPERIMENT. 



74 1 



Now, how would we perform this experiment to-day and with 

 what results ? Having flown big kites during thunderstorms, it 

 may perhaps be best to describe step by step two of these experi- 

 ments, and then speak of what we know can be done, but as yet 

 has not been done. 



Our first repetition of Franklin's kite experiment was at Blue 

 Hill' Observatory, some ten miles southwest of Boston, one hun- 

 dred and thirty- three years after its first trial. There were 

 two large kites silk-covered and tin- foiled on the front face. 

 These kites were of the ordinary hexagonal shape, for in 1885 

 Malay and Hargrave kites were all unknown to us. Fifteen hun- 

 dred feet of strong hemp fish line were wrapped loosely with un- 

 covered copper wire of the smallest diameter suitable, and this 

 was brought into a window on the east side of the observatory, 

 through rubber tubing and blocks of paraffin. Pieces of thor- 

 oughly clean plate glass were also 

 used. Materials capable of giving a 

 high insulation were not so easily 

 had then as now. We knew very lit- 

 tle about mica ; and quartz fibers and 

 Mascart insulators could not be ob- 

 tained in the United States. Our elec- 

 trometer, however, was a great im- 

 provement upon any previous type, 

 and far removed from the simple 

 pith- ball device used by Franklin. 

 Knowing that an electrified body free 

 to move between two other electri- 

 fied bodies will always move from 

 the higher to the lower potential, 

 Lord Kelvin devised an instrument 

 consisting of four metallic sections, 

 symmetrically grouped around a 

 common center and inclosing a flat 

 free - swinging piece of aluminum 

 called a needle. The end of the kite 

 wire is connected with the needle and 

 the sections or quadrants are alter- 

 nately connected and then electrified, one set with a high posi- 

 tive potential, say five hundred volts, and the other with a cor- 

 responding negative value, say five hundred volts lower than the 

 ground. 



Perhaps the most noteworthy result of these earlier experi- 

 ments was the discovery (for such we think it was) that showery 

 or thunderstorm weather was not the only condition giving 

 marked electrical effects. The electrometer needle would be vio- 



MASCART ELECTROMETER. 



