3 1 2 Means of producing Elcftruity. [Book IV. 



tains fome other matter in combination with it, of the 

 nature of which we are as yet uninformed ; and it is 

 probably this combination of foreign matter which 

 difables it, in ordinary cafes, from penetrating glafs. 

 Let it, however, be carefully remembered, that this is 

 fpeculation and conjecture, and that we at prefent know 

 nothing of a certainty concerning the electrical fluid, 

 but fome of its effects. 



Electrical phenomena are produced by friction, and 

 by communication. In general, bodies which electrify 

 the beft by friction, electrify the word by communi- 

 cation (except glafs in certain circumftances) and on 

 the contrary, fubftances which electrify the bed by 

 communication electrify the worft by friction. I (hall 

 begin with thofe experiments which gave rife to the 

 principal technical terms made ufe of in this fcience. 



If a dry glafs tube is rubbed with a piece of dry 

 filk, and if light bodies, as feathers, pith balls, &c. are 

 prefented to it, they will be firft attracted, and then re- 

 pelled. The beft rubber for a fmooth glafs tube is a 

 piece of black or oiled filk, on which a little amalgam 

 has been fpread; fealing wax, rubbed with new and 

 foft flannel, will produce the fame effect. By this fric- 

 tion an agent or power is put in action, and this power 

 is called the electrical fluid ; a certain quantity of this 

 fluid is fuppofed to exift latent in all bodies, in which 

 ftate it makes no impreflion on our lenfes, but when 

 by the powers of nature or of art, this equilibrium is 

 dcftroyerl, and the agency of the fluid is rendered per- 

 ceptible to the fenfes, then thofe effects are produced 

 which are termed electrical, and the body is laid to be 

 electrified. 



If a homogeneous body is prefented to the excited 

 tube, fo as to receive electricity from it, and the elec- 

 tricity 



