26 STATIC ELECTRICITY 



now it is on two bodies. Again, charging the second body 

 oppositely to the first before inserting it into the can, and keeping 

 the can untouched to earth until both conductors are within it 

 but not in contact, if we now bring them together the smaller 

 charge will be entirely neutralised by a part of the larger and will 

 disappear, while the rest of the larger charge will spread over both 

 bodies. But the electroscope remains unaffected l)y this process, 

 or the algebraic sum is still the same. The two kinds have, 

 therefore, disappeared in equal amounts. 



Electrification by induction. Returning to the first of the 

 two preceding experiments, while the second uncharged body 

 was being lowered into the can it became electrified bv induction 

 on approaching the charged body. This we know from our 

 general experiments on induction, described in Chapter I. Since 

 the electroscope gave no indication of change of amount, it is 

 evident that equal and opposite amounts must have been induced 

 on the body. The unlike was near the first body, the like mimic 

 from it. On contact the unlike was neutralised bv some of the 

 charge on the first body. So that it is again evident that the t\\o 

 kinds disappeared in equal amounts. 



Electric current. We shall see hereafter thai UK clec trie- 

 current as produced by voltaic cells or dynamos may he regarded 

 as a conduction of electrification along the win- in which it occurs. 

 The quantities conducted even in a short time arc- usually 

 enormously great compared with the quantities with which \\e 

 deal in experiments with the gold-leaf electroscope on cha: 

 produced by friction or induction. Making a small voltaic cell, 

 and connecting the plates together by a \\ire M> thai the current 

 flows, let us insert it within the electroscope can. No \<-ti'm of 

 charge is shown. Hence the two kinds are being produced and 

 are disappearing in equal quantiti 



The distribution of electrification on conductors. 



Electrification /v.v/Vr.v only vn the out side surface of conductor*. 

 unless, being hollow, they contain insulated charged bodiix. 



If the deep can of the previous experiments, or preferably a 

 hollow insulated metal globe with a small opening to the inside, i- 

 charged in any way, a proof plane inserted inside through the 

 opening by an insulating holder and brought into contact with Ihe 

 inside shows no trace of electrification on withdrawal. Or, if a 

 charged conductor is brought within the hollow conductor and 

 touched to it, it is entirely discharged. On contact it forms parl 

 of the inside of the hollow conductor and can no longer keep its 

 electrification. 



Faraday (E.i'j). KM. vol. i. 1173-4) made experiments on a 

 large scale to show that the charge of a conductor resides on the 

 outside. A cube with each edge 12 ft. Ion;/, consisting of a light 

 wooden framework covered in with paper, was made thoroughlv 

 conducting by copper wire and bands of tinfoil. It was insulated 



