460 THE) INTELLECTUAL RISE IN ELECTRICITY. 



concludes Hauksbee, whose fascination with his work 

 shows itself now in every line of his description, that 

 sort of light does not resemble the little bluish radiance in 

 the barometer ! What is it? 



He undertakes to find out by noting the conditions un- 

 der which he can produce a similar light. He arranges a 

 piece of amber so that he can revolve it swiftly in contact 

 with a pad of woolen cloth within his exhausted glass 

 vessel. The light appears; he can see it at a distance of 

 three or four feet. It is brighter as the vacuum increases; 

 but then the amber begins to burn and the woolen scorches. 

 Did the heat so produced make the light? 



Try flint and steel, and see, his active brain answers. 

 A steel ring is made to revolve in the glass vessel and a 

 bit of flint is pressed against it. Before the air is ex- 

 hausted the sparks fly in showers, but as the air-pump 

 draws out the reluctant atmosphere they fade and finally 

 disappear, and only a just perceptible luminous ring where 

 the stone touches the whirling metal at last remains. No; 

 it is not the flint and steel light which needs the air this 

 unearthly glow, which thrives best when the air is gone. 



Singular, that this light, so like the lightning, should 

 have been produced in an exhausted glass bulb, and 

 almost two hundred years ago ! 



Hauksbee now determines that the mercury light on the 

 whole is more like the amber glow than like the corusca- 

 tions flying from the steel; but as amber is resinous and 

 inflammable he substitutes glass as the material to be 

 rubbed, and makes a new discovery. The light in the ex- 

 hausted receiver becomes purple; but, as the air is let into 

 the vessel, it fades, turns reddish, and then gray very 

 feeble when the vessel is full of aii. It is odd how the 

 color changes as more or less air is admitted; odder still 

 that there should be flashes and no longer a glow when the 

 woolen rubber is soaked with a saltpeter solution. He 

 rubs glass on glass, glass on oyster shells, oyster shells on 

 woolen, sometimes in vacuo, sometimes in air; puzzling 



