78 Britain's Heritage of Science 



and made some interesting experiments on the intensity of 

 sound transmitted through air of different densities. 



Hauksbee deserves, perhaps, most to be remembered 

 by his researches in electricity. Frequent references occur 

 in the publications of the time to the curious luminosity 

 in the partial vacuum above the barometer column which 

 occasionally appears when the mercury is made to oscillate 

 in the dark. Hauksbee had the idea that the luminosity 

 was connected with some electrical action. To test this, 

 he mounted a spherical glass vessel so that it could be made 

 to rotate round a central axis. The vessel was exhausted, 

 and, being set in motion, became highly electrified by 

 friction when the hand was placed against it. At the same 

 time the remnant of air in the vessel became luminous, 

 and Hauksbee rightly concluded that the luminosity was of 

 the same nature as that observed in the barometer; in 

 the latter case, of course, the friction is produced internally 

 between the moving mercury and the glass. Incidentally 

 it may be mentioned that the first record of an electric 

 spark occurs in Hauksbee 's writing; it was produced by 

 approaching the finger towards the electrified glass vessel, 

 and is said to have been an inch long. 



Very little is known about the life of Hauksbee, or of 

 that of Stephen Gray and Granville Wheler, two other 

 important contributors to our knowledge of electricity. 

 Gray, elected a Fellow of the Royal Society in 1732, was 

 the first to point out the effects of conductivity in electrical 

 experiments, classifying bodies as conductors or insulators. 

 He had been led to this fundamental distinction by 

 experimenting with a glass tube which was closed at one 

 end by a cork, and noting that, when the glass was excited 

 by friction, the cork attracted light bodies, thus showing 

 that it had become electrified. When a rod several feet 

 in length carrying an ivory sphere at its further end was 

 inserted in the cork, the sphere also became electrified. 

 When other experiments did not give the expected result, 

 Gray seems to have consulted another Fellow of the Royal 

 Society, Granville Wheler, a clergyman, who suggested to 

 him that the cause of the failure was likely to be due to the 

 difficulty of supporting the bodies experimented upon in 



