On Electric Phenomena. 11 



Is the tension of the electricity on the conductor so great, 

 that it can no longer be held back by the resistance of the 

 air, then, of course, the conductor cannot absorb any more 

 electricity, however much may be conveyed to it. If we, how- 

 ever, place the conductor opposite to another, which is con- 

 nected with the earth, then the positive electricity of the first 

 conductor attracts the negative electricity of the second, and 

 repels the positive, which escapes towards the ground. The 

 two opposite electricities in the two conductors so attract each 

 other, that their tension towards the surface is essentially im- 

 paired, and just on that account we can convey much more 

 electricity to the first conductor, than it would be possible to 

 do in any other case. This reciprocal union of the two elec- 

 tricities — as it is called by natural philosophers — occurs 

 in its fullest perfection, when the conductors take the form of 

 large smooth surfaces, which stand very near and parallel to 

 one another. But to prevent the union of the electricities, 

 which attract one another, a good insulator is placed between 

 them, for instance: a glass plate. Thus an apparatus is formed 

 which is called after its inventor "Franklin's plate"; a sheet 

 of glass which is covered on both sides with a thin coating 

 of tin-foil. If the two surfaces are curved, then we have a 

 Kleist's or Leyden Phial or Jar, a glass phial or jar coated 

 inside and outside with tin-foil. A metallic rod, having a 

 knob at the top, is fixed into the mouth of the jar, and is 

 made to communicate with the inside coating, while the out- 

 side is placed in communication with the ground. If we es- 

 tabhsh a communication between the inside and outside coating 

 of such a jar by means of a conductor, the opposite electri- 

 cities re-unite themselves, and the jar is discharged. A cur- 

 rent of electricity flows through the conductor. If we insert 



(133) 



