PROGRESS IN ELECTRICITY 



remain in a state of equilibrium, just as fluids natural- 

 ly tend to seek a level. But it may, nevertheless, be 

 raised or lowered, and this equilibrium be thus dis- 

 turbed. If a body has more electricity than its normal 

 amount it is said to be positively electrified; but if it 

 has less, it is negatively electrified. An over-electrified 

 or " plus " body tends to give its surplus stock to a body 

 containing the normal amount; while the "minus" 

 or under -electrified body will draw electricity from 

 one containing the normal amount. 



Working along lines suggested by this theory, Frank- 

 lin attempted to show that electricity is not created by 

 friction, but simply collected from its diversified state, 

 the rubbed glass globe attracting a certain quantity of 

 "electrical fire," but ever ready to give it up to any 

 body that has less. He explained the charged Leyden 

 jar by showing that the inner coating of tin-foil received 

 more than the ordinary quantity of electricity, and in 

 consequence is positively electrified, while the outer 

 coating, having the ordinary quantity of electricity 

 diminished, is electrified negatively. 



These studies of the Leyden jar, and the studies of 

 pieces of glass coated with sheet metal, led Franklin to 

 invent his battery, constructed of eleven large glass 

 plates coated with sheets of lead. With this machine, 

 after overcoming some defects, he was able to produce 

 electrical manifestations of great force a force that 

 "knew no bounds," as he declared ("except in the 

 matter of expense and of labor"), and which could be 

 made to exceed " the greatest know effects of common 

 lightning." 



This reference to lightning would seem to show 



289 



