On the Constitution of the Electric Fluid. 131 



has strikingly proved the necessity of the direct application of 

 both poles, if proof were wanted, by perfectly insulating 320 

 cells of his great water-batteiy, connecting one pole with the 

 ground, and the other with solution of iodide of potassium. In 

 this state no decomposition resulted ; but when both polar wires 

 were placed in connexion with the iodide, decomposition took 

 place, and iodine was freely evolved*. Faraday has given an- 

 other instance : if two insulated voltaic troughs be placed in the 

 same right line, the two adjoining ends being connected by a 

 wire over which is suspended a magnetic needle, thei'e will be no 

 deflection ; but as soon as the two distant ends are connected, 

 deflection takes placet- 



In the decompositions effected by Faraday by means of common 

 electricity, it is remarkable that he made use of but one pole, 

 and that the positive. The wire connected with the positive 

 conductor of the electrical machine was the only real and legiti- 

 mate pole concerned. The wire which carried ofl" the electricity 

 to the gas and water-pipes was not in the negative state ; and if 

 of sufficient thickness, was not in any electric state ; for it trans- 

 mitted to the general reservoir as fast as it received the electri- 

 city, and manifested no electrical properties. It is veiy true, 

 that if an insulated conductor be approached within a short di- 

 stance of one that is also insulated and electrified, the former 

 will become electrical by induction, one end being positive, the 

 other negative ; but if the conductor thus electrified by induction 

 be made to communicate with the ground, its electrical state is 

 destroyed. In the case of Faraday's wire which carried ofl" elec- 

 tricity to the discharging train, it cannot be supposed to be in 

 the negative state caused by induction ; for induction can only 

 be manifested when an insulating medium is interposed between 

 the two conductors concerned J. In the present instance, the 

 interposed medium was a saline solution, an excellent conductor 

 of the electricity which an excited electrical machine is capable 

 of transmitting in a cui-rent. Beside all this, induction should 

 not enter into the comparison of frictional with voltaic electricity, 

 as no such thing is known or acknowledged in voltaic electricity 

 unless as an hypothesis. Here, then, was decomposition with 

 one pole only ; and hence there was no analogy with voltaic de- 

 composition, for this always requires the cooperation of the two 

 poles. 



Should any suspicion relative to the influence of induction be 

 entertained, Faraday's own words prove that he did not conceive 

 such an influence to be in operation. A bit of turmeric paper, 



♦ Pliil. Mag., Oct. 1844, p. 290. t Researches, par. 282. 



X " Induction can only fake place tlirou};h or across insulators." — Fara- 

 day's llesearciies, i)ar. 1678. 



K2 



