338 Mr. M. Donovan on the supposed Identity of the Agent 



galvanometer of 500 turns of wire doubly covered with silk, each 

 series of turns being separated by varnished taffetas, the devia- 

 tion produced by the same machines was almost tenfold. Hence 

 in Faraday's galvanometer, the silk was capable of carrying as 

 much electricity as produced 40° or 41° of deflection*; and 

 anything more than this quantity was probably transmitted late- 

 rally from wire to wire without passing' through. He does not 

 inform us what the amount of deflection was in these experi- 

 ments j we therefore have no evidence of its agreement with the 

 deflection produced by other charges of the Leyden battery. 



But it is stated that the transmission of the charge through 

 the different wet strings produced equal deflection, whatever its 

 amount might have been. "With the thick string, the charge 

 passed at once :" this cannot be intended to be literally under- 

 stood, for then the discharge would constitute an explosion ; the 

 discharge must therefore be understood as having taken place in 

 an exceedingly rapid current. " With the thin string, it occupied 

 a sensible time;" that is, the current was not quite so rapid, yet 

 still the period was so short that it was barely sensible. " And 

 with the thread, it required two or three seconds before the elec- 

 trometer fell entirely down." 



We must carefully consider what happens when a Leyden 

 battery is discharged, by a wet string, through a galvanometer. 

 The charge of the battery in all Faraday's trials was the same, 

 and would therefore in all the three cases make the same effort 

 to pass at once, but would be retarded more or less according to 

 circumstances. The circumstances which modify the passage of 

 the electric discharge are the thickness, humidity, and length of 

 the strings : as to the conducting power of the liquid with which 

 the strings were moistened, it need not be considered in the case 

 of common electricity. Faraday himself says, " the tension of 

 machine electricity causes it, however small in quantity, to pass 

 through any quantity of water, solutions, or other substances 

 classing with these as conductors, as fast as it can be producedf." 

 The only modifying influence which these three circumstances 

 can exert, is to retard the velocity of the discharge; and yet the 

 discharge must take place with all the velocity that the modi- 

 fying circumstances will permit. This velocity, although some- 

 what retarded, is still very great. The intensity of the electri- 

 city confined in a Leyden battery is also very great ; and that 

 intensity will be communicated to a string wet with so good a 

 conductor of common electricity as water is known to be, although 

 it is not a perfect one. The electrical intensity of the string 

 must be the same as that of the battery ; and the quantity of 

 electricity in the string at any one moment is as great as its 



♦ Researches, pars. 297, 302, and 367. t Ibid. par. 453. 



