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POPULAR SCIENCE MONTHLY. 



ratus was at hand. It may seem ridiculous, but we hauled nearly 

 a wagon-load of electrical apparatus to the summit of the hill, 

 and found occasion to use all of it. Our insulators were delicate 

 glass vessels, curiously shaped, containing sulphuric acid, and 



KiTE-FLYINO ON RoOF OF CiTY BuiLDINCi. 



able to hold with little leakage the highest known potentials. 

 Besides these fine Mascart insulators, we had hundreds of dis 

 tilled-water batteries and two electrometers, one a Mascart quad- 

 rant, the other a large multiple quadrant. The chief aim that 

 year was to secure by mechanical means (discarding the photo- 

 graphic and eye methods) a continuous record of the potential. 

 When we can study the potential at any moment and still have a 

 record of it, the relation of the electricity of the air to the pres- 

 sure, temperature, and moisture will be more easily investigated. 

 Among our records that year there is one date, June 30, 1891, 

 where a direct comparison of the electrification of the air fifteen 

 or twenty feet from the ground and at a height of about five 

 hundred feet is shown. In one, the potential was obtained by a 

 water-dropper collector from a second- story window in the ob- 

 servatory, and in the other was obtained by means of the kite. 

 It will be seen how much higher the kite values are, although the 

 kite was a much slower accumulator of electricity. In the next 

 year, 1892, the kite was flown several times during thunder- 

 storms, but generally during afternoon storms ; and in the lull 



