A HISTORY OF SCIENCE 



the air in a receiver containing some mercury, he found 

 that by allowing air to rush through the mercury the 

 metal became a jet thrown in all directions against the 

 sides of the vessel, making a great, flaming shower, 

 "like flashes of lightning," as he said. But it seemed 

 to him that there was a difference between this light 

 and the glow noted in the barometer. This was a 

 bright light, whereas the barometer light was only a 

 glow. Pondering over this, Hauksbee tried various 

 experiments, revolving pieces of amber, flint, steel, and 

 other substances in his exhausted air-pump receiver, 

 with negative, or unsatisfactory, results. Finally, it 

 occurred to him to revolve an exhausted glass tube 

 itself. Mounting such a globe of glass on an axis so 

 that it could be revolved rapidly by a belt running on 

 a large wheel, he found that by holding his fingers 

 against the whirling globe a purplish glow appeared, 

 giving sufficient light so that coarse print could be read, 

 and the walls of a dark room sensibly lightened sever- 

 al feet away. As air was admitted to the globe the 

 light gradually diminished, and it seemed to him that 

 this diminished glow was very similar in appearance 

 to the pale light seen in the mercurial barometer. 

 Could it be that it was the glass, and not the mercury, 

 that caused it ? Going to a barometer he proceeded to 

 rub the glass above the column of mercury over the 

 vacuum, without disturbing the mercury, when, to 

 his astonishment, the same faint light, to all appear- 

 ances identical with the glow seen in the whirling globe, 

 was produced. 



Turning these demonstrations over in his mind, he 

 recalled the well-known fact that rubbed glass attracted 



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