respecting the Vhcenomena of Electricity . 1 05 



restore from the ground the electric fluid carried away to tlie 

 prime conductor by the spindle, the gold- leaf of the electro- 

 meter diverges as positive, though the rubber is of the same sub- 

 stance as the spindle. This is a peremptory demonstration that 

 the effect oijriclion is not to open the pores for receiving more 

 electric matter, which is discharged when the friction ceases, as 

 Mr. Donovan conceives it : since both bodies, which in this case 

 exercise friction on each other, are of the same glass. 



33. Exper. 4, p. 10, shows that sealing-wax, used as rub- 

 ier over the glass spindle, becomes strongly negative, and renders 

 the glass strongly positive. And thus it is directly proved, that 

 the cause of sealing-wax being rendered ?zegative hy friction 

 with the glass, is that the latter takes some electric fluid from 

 seaUng-'ivax, which effect could not have been ascertained with- 

 out the two electrometers. 



34. Now, in Exper. 1, a brass rubber applied to the glass cy- 

 linder is seen to become negative, and the glass cylinder made 

 positive; but in Exper. 6, having covered a glass cylinder with 

 a thick coating of sealing-ivax, producing in fact a sealing- 

 wax cylinder, the same brasi rubber was rendered positive. These 

 experiments compared with each other, further demonstrate the 

 real electric effect of friction. But the next experiment will 

 place it beyond all doubt. 



35. Exper. 8 is made with what is called India beads, the 

 size and colour of a cherry: they are made, as I have been in- 

 formed, of an inspissated vegetable oil, very elastic, not soluble 

 in water. I placed one on a glass spindle, and fitted to its shape 

 two narrow r?ibbers, one of naked brass, the other of brass co- 

 vered with sealing-wax. With a very small motion of the winch, 

 that bead became negative, and the naked brass rubber became 

 positive; but the same bead became positive when the brass 

 rubber was covered with sealing-wax and this rubber was made 

 negative, 



3G. These experiments afford a true analysis of the electric 

 effects of friction. Its general effect, as I have stated, is to set 

 in motion the electric fluid residing on the surface of the bodies 

 which are rubbed ; and the consecjuence of that effect is, that the 

 body which recedes from the point o{ friction carries along with 

 it a part of that electric fluid ; which effect extends even to the 

 case when the rubber and the body rubbed are of the same sub- 

 stance, when the latter suddenly recedes, and meet in its way a 

 conductor, before returning to the rubber, 



37. These ex])criments remove the difficulty which Mr. Do- 

 novan found (p. 331)) to reconcile the (supposed) equal distri- 

 bution of the electric fluid with tlie impermeability of glass. The 



equal 



