302 Prof. Faraday on Electric Induction — 



which gradually travelled along it, and made itself evident at 

 successive intervals of time in different parts of the wire. It 

 was even possible, by adjusted touches of the battery, to have 

 two simultaneous waves in the wire following each other, so that 

 at the same moment that c was affected by the first wave, a or b 

 was affected by the second ; and there is no doubt that by the 

 multiplication of instruments and close attention, four or five 

 waves might be obtained at once. 



If after making and breaking battery contact at a, a be imme- 

 diately connected with the earth, then additional interesting 

 effects occur. Part of the electricity which is in the wire will 

 return, and passing through a will dellect it in the reverse direc- 

 tion ; so that currents will tiow out of both extremities of the 

 wire in opposite directions, whilst no current is going into it 

 from any source. Or if a be quickly put to the battery and then 

 to the earth, it will show a current first entering into the wire, 

 and then retvuning out of the wire at the same place, no sensible 

 part of it ever travelling on to h or c. 



When an air wire of equal extent is experimented with in like 

 manner, no such effects as these are perceived ; or if, guided by 

 principle, the arrangements are such as to be searching, they are 

 perceived only in a very slight degree, and disappear in com- 

 parison with the former gross results. The effect at the end of 

 the very long air wire (or c) is in the smallest degree behind the 

 effect at galvanometer a ; and the accumulation of a charge in 

 the wire is not sensible. 



All these results as to time, &c. evidently depend upon the 

 same condition as that which produced the former effect of static 

 charge, namely, lateral induction ; and are necessary consequences 

 of the principles of conduction, insulation and induction, three 

 terms which in their meaning are inseparable from each other 

 (Exp. Res. 1320, 1326*, 1338, 1561, &c.). If we put a plate 



* 1326. All these considerations impress my mind strongly with the 

 conviction, that insulation and ordinary conduction cannot be properly 

 separated when we are examining into their natm-e ; that is, into the general 

 law or laws under which their phicnomeua are produced. They apjjcar to 

 me to consist in an action of contiguous p.irticles, dependent on the forces 

 developed in electrical excitement : these forces bring the particles into a 

 state of tension orpolai'ity, which constitutes both induction and insulation ; 

 and being in this state, the contiguous particles have a power or capabihty 

 of communicating these forces, one to the other, by which they are lowered 

 and discharge occurs. Every body appears to discharge (444 987) ; but 

 the possession of this capability in a greater or smaller degree in different 

 bodies makes them better or w orsc conductors, worse or better insulators : 

 and both induction and conduction a))pear to be the same in their principle 

 and action (1320.), except that in the latter an effect common to both is 

 raised to tlie highest degree, whereas in the former it occurs in the best 

 cases in only an almost insensible quantity. 



