86 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XII.) 



insulating power. Of the numerous well known cases fitted to show this resistance 

 in ,what are called the perfect conductors, the experiments of Professor Wheatstone 

 best serve my present purj5ose, since they were carried to such an extent as to show 

 that time entered as an element into the conditions of conduction* even in metals. 

 When discharge was made through a copper wire 2640 feet in length, and -V^h of 

 an inch in diameter, so that the luminous sparks at each end of the wire, and at the 

 middle, could be observed in the same place, the latter was found to be sensibly be- 

 lli nd the two former in time, they being by the conditions of the experiment, simul- 

 taneous. Hence a proof of retardation ; and what reason can be given why this re- 

 tardation should not be of the same kind as that in spermaceti, or in lac, or sulphur ? 

 But as, in them, retardation is insulation, and insulation is induction, why should we 

 refuse the same relation to the same exhibitions of force in the metals ? 



1329. We learn from the experiment, that if time be allowed the retardation is 

 gradually overcome ; and the same thing obtains for the spermaceti, the lac, and 

 glass ; give but time in proportion to the retardation, and the latter is at last van- 

 quished. But if that be the case, and all the results are alike in kind, the only dif- 

 ference being in the length of time, why should we refuse to metals the previous in- 

 ductive action, which is admitted to occur in the other bodies ? The diminution of 

 time is no negation of the action ; nor is the lower degree of tension requisite to 

 cause the forces to traverse the metal, as compared to that necessary in the cases of 

 water, spermaceti, or lac. These differences would only point to the conclusion, that 

 in metals the particles under induction can transfer their forces when at a lower de- 

 gree of tension or polarity, and with greater facility than in the instances of the 

 other bodies. 



1330. Let us look at Mr. Wheatstone's beautiful experiment in another point of 

 view. If, leaving the arrangement at the middle and two ends of the long copper 

 wire unaltered, we remove the two intervening portions and replace them by wires of 

 iron or platina, we shall have a much greater retardation of the middle spark than 

 before. If, removing the iron, we were to substitute for it only five or six feet of 

 water in a cylinder of the same diameter as the metal, we should have still greater 

 retardation. If from water we passed to spermaceti, either directly or by gradual 

 steps through other bodies, (even though we might vastly enlarge the bulk, for the 

 purpose of evading the occurrence of a spark elsewhere (1331.) than at the three 

 proper intervals,) we should have still greater retardation, until at last we might arrive, 

 by degrees so small as to be inseparable from each other, at actual and permanent 

 insulation. What, then, is to separate the principle of these two extremes, perfect 

 conduction and perfect insulation, from each other ; since the moment we leave in 

 the smallest degree perfection at either extremity, we involve the element of perfec- 

 tion at the opposite end ? Especially too, as we have not in nature the case of perfec- 

 tion either at one extremity or the other, either of insulation or conduction. 



* Philosophical Transactions, 1834, p. 583. 



