CHAP, i.] ELECTRICITY AND MAGNETISM. 



55 



B to the side nearest the glass, and a fresh supply of -h 

 electricity will come from the machine. Thus, again, 

 this arrangement will become an accumulator of the two 

 electricities. If the two brass discs are pushed up close 

 to the glass plate the electricities will attract one another 

 still more strongly, because they are now nearer one 

 another, and the inductive action will be greater ; hence 

 a still larger quantity of electricity can be accumulated 

 in the plates. We see then that the capacity of an 

 accumulator is increased by bringing the plates near 

 together. ^If now, while the discs are strongly charged, 

 the wires are removed and the discs are drawn backwards 

 from one another, the two electricities will no longer 

 hold one another bound so strongly, and there will be 

 moi'Q/ree electricity 

 than before over c 



their surfaces. This 

 would be rendered 

 evident to the ex- 

 perimenter by the 

 little pith-ball elec- 

 troscopes fixed to - 

 them (see the Fig.),I 

 which would fly out Fig> 3a 



as the brass discs 



were moved apart. We have put no further charge on 

 the disc B, and yet, from the indications of the electroscope, 

 we should conclude that by moving it away from disc A 

 it has become electrified to a higher degree. The fact is, 

 that while it was near the - electricity of A the capacity 

 of the conductor B was greatly increased, but on moving 

 it away from B its capacity has diminished, and hence 

 the same quantity of electricity now electrifies it to a 

 higher degree of potential. The presence, therefore, of 

 an earth-connected plate near an insulated conductor 

 increases its capacity, and permits it to accumulate a 

 greater charge by attracting and condensing the elec- 



