NATURAL H I S T O RY of iV*0 $ JFA T. 



tion concerning eledricity. The fcope of his demonftrations is 

 fomething different, viz. to fhew the true caufe of the afcent of 

 rain-water, and the power by which it remains floating in the 

 air, which is at all times much lighter than water. But as the 

 investigation of one truth often proves introductory to another, 

 fo in this paifage the writer feems. to direct us to a clearer infight 

 into the origin and nature of the north-light. I mail therefore 

 infert fo much of that paflage here, as relates to our purpofe. 

 In order to apprehend his meaning, we muft recollect with the 

 learned writer, that Mr. Du Fay's obfervation, " that there are 

 two forts of eledricity," is proved by obfervations and experiments ; 

 and that the electrical bodies of a vitreous electricity mutually 

 repel one another, whilft they attract thofe of a refmous eledrici- 

 ty ; alfo that thofe of a refinous electricity repel one another, and 

 attract thofe of a vitreous electricity. 



" I fuppofe, fays Dr. Defaguliers, particles of pure air to be 

 eledric bodies always in a ftate of electricity, and that vitreous 

 electricity. 



lit, Becaufe particles of air repel one another without touch- 

 ing, as has been deduced from experiments and obfervations. 



2dly, Becaufe when the air is dry, the glafs-tube rubb'd (or 

 only warmed) throws out its effluvia, which the air drives back 

 to the tube; from whence they dart out anew, and fo move 

 backwards and forwards with a vibratory motion, which conti- 

 nues their electricity. 



3dly, Becaufe the feather made electric by the tube, and 

 darted from it, keeps its eledricity a long time in dry air; 

 whereas when the air is moift, the moift particles, which are non- 

 electrics, floating in the air, and being attracted by the feather, 

 adhere to it, and foon make it lofe its eledricity; which alfo 

 happens even to the tube in a little time. 



From this confideration it will be eafy to account for a famous 

 experiment of the late Mr. Haukfbee, which is this : 



Having pump'd out all the air from a glafs-globe, he caus'd it 

 to turn on its axis very fwiftly by means of a rope with a wheel 

 and pulley; then rubbing the glafs with his hand during its mo- 

 tion, there appear'd a great deal of light of a purple colour within 

 the globe, without any light or attradion obferv'd on the outfide 

 of the glafs, which is obferv'd when the air has not been pump'd 



Part I. D u 



