74 



POPULAR SCIENCE MONTHLY. 



Franklin's Elkcteical Machine. 



rose at his entrance ; and he constructed and worked with other 

 electrometers ; but for us that first experience will always possess 

 a peculiar interest. The kite and the electrometer betray the in- 

 tention of the colonial scientist to ex- 

 plore the free air, and, reaching out 

 from earth, study air electrification in 

 situ. He made the beginning by iden- 

 tifying the lightning Hash with the 

 electricity developed by the frictional 

 machine of that time. A hundred pa- 

 tient philosophers have carried on the 

 work, improving methods and appa- 

 ratus, until to-day we stand upon the 

 threshold of a great electrical survey of 

 the atmosphere. It is no idle prophecy 

 to say that the twentieth century will 

 witness wonderful achievements in 

 measuring the potential of the light- 

 ning flash, in demonstrating the nature 

 of the aurora, and in utilizing the elec- 

 trical energy of the cloud. The im- 

 proved kite and air-runner will be the 

 agency through which these results will be accomplished. 



The famous kite experiment is described by Franklin in a let- 

 ter dated October 19, 1752 : " Make a small cross of light sticks 

 of cedar, the arms so long as to reach to the four corners of a 

 large, thin silk handkerchief when extended. Tie the corners of 

 the handkerchief to the extremities of the cross, so you have the 

 body of a kite which, being properly accommodated with a tail, 

 loop, and string, will rise in the air like those made of paper, but 

 being made of silk is better fitted to bear the wet and wind of a 

 thunder gust without tearing. To the top of the upright stick of 

 the cross is to be fixed a very sharp-pointed wire rising a foot or 

 more above the wood. To the end of the twine next the hand is 

 to be tied a silk ribbon, and where the silk and twine join a key 

 may be fastened. This kite is to be raised when a thunder gust 

 appears to be coming on, and the person who holds the string 

 must stand within a door or window, or under some cover, so that 

 the silk ribbon may not be wet ; and care must be taken that the 

 twine does not touch the frame of the door or window. As soon 

 as the thunder clouds come over the kite, the pointed wire will 

 draw the electric fire from them, and the kite, with all the twine, 

 will be electrified, and stand out every way and be attracted by 

 an approaching finger. And when the rain has wet the kite and 

 twine you will find the electric fire stream out plentifully from 

 the key on the approach of your knuckle." 



