Hiftory ofDifcoveries, &V. [Book IV. 



vitreous, depended chiefly upon the nature of the fur- 

 face j for that a glafs tube, when the polifhed furface 

 was deltfoyed, exhibited proofs of negative electricity 

 as much as fulphur or fealing wax, and drew fparks 

 from the knuckle when applied to it, inftead of giving 

 fire from its own body ; when the tube was greafed, 

 and a rubber with a rough furface was applied to it, 

 its pofitive power was reftored, and the contrary, when 

 the rubber became fmooth by friction. 



At this period it may not be improper to clofe my 

 (ketch of the difcoveries relating to electricity ; fmce 

 the fole object of thefe narratives, in this work, is to 

 conduct the reader to a more ready apprehenfion of 

 the fcience, it would be ufelefs to lead him into the 

 minutias of it before he was made properly acquainted 

 with the general principles. 



