VOL. XLVin.j PHrLOSOPHICAL TRANSACTIONS. 435 



not make any sensible alteration in the electricity of the air, except when they 

 are moist. In the most dry nights of that summer, he could observe no signs 

 of electricity in the air ; but it returned in the morning, as before said, when 

 the sun began to appear above the horizon, and vanished again in the evening, 

 about half an hour after sun-set. The strongest common electricity of the at- 

 mosphere was perceived in the month of July, on a very dry day, the heavens 

 being very clear, and the sun extremely hot. The distance of 10 or 12 lines was 

 then sufficient for the approach of the dust to the conductor, in order to see 

 the particles rise in a vertical direction, like the filings of iron on the application 

 of a magnet. 



OL's. 5. — June 27, at 2 afternoon, he perceived some stormy clouds rising 

 above the horizon, and immediately went up to his apparatus ; and having ap- 

 plied the dust to the key, it was attracted with a force which increased in pro- 

 portion as the clouds reached the zenith. When they had come nearly over the 

 wire, the dust was so impetuously repelled as to be entirely scattered from the 

 paper. He drew considerable sparks from it, though there was neither thunder 

 nor lightning. These sparks were of a very lively red colour when attracted 

 with the finger : they were white and smaller when he used a wire hafted in a 

 glass tube : they were bluish, and much extended, when attracted by spirit of 

 wine in a silver spoon. 



Obs. 6. — He applied a piece of resin to the conductor, but could draw no 

 sparks from it : however, all who were present heard a noise like that of hairs 

 when burnt. It was the same with sealing-wax, woollen-cloth, linen, &c. He 

 then took a quicksilvered glass, and applied to the clean side a piece of wire of 6 

 inches long, while the other end was put to the conductor ; by which he drew a 

 multitude of small whitish sparks, which soon ceased, but were succeeded by a 

 noise like that which happened on applying the resin to the conductor. 



When he applied the end of the wire to the silvered surface of the glass, while 

 the other end touched the conductor, the quicksilver affected him so strongly, 

 that notwithstanding his being so much accustomed to suffer these electrical 

 shocks, he was not able to bear this. Hence he concludes, that the best me- 

 thod of increasing the electrical power is to make it fall on some metalline sur- 

 face, intimately connected with a surface that is an electric per se. 



Oi.v. 7. — When the stormy clouds were in the zenith of the wire, the electri- 

 city was increased to so high a point, that the silken thread attracted light bodies 

 at the distance of 7 or 8 inches. This cord was 6 feet long, and in the first foot 

 the electricity was nearly as strong as in the wire, but from thence it diminished 

 in the rest of the length. He substituted a glass tube for the silken cord, and 



3 k2 



