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



It is very probable that Professor Faraday was induced to 

 adopt the discharging train, as a substitute for the negative pole, 

 by his peculiar ^^ew-s of the nature of voltaic excitement. In 

 his theory, it is assumed that the current of electricity is gene- 

 rated by the chemical action of the oxygen of the exciting fluid 

 on the zinc, a state of polar tension being the result, which is 

 immediately relieved by the conducting power of the copper plate ; 

 and through this plate the electricity passes oflp. Here it is evi- 

 dent that the duty assigned to the copper plate is that of a mere 

 conductor ; and this is precisely the function attributed to the 

 copper wii-e attached to the discharging train in the experiments 

 with common electricity just described. Such, however, appears 

 inconsistent with some well-known facts. On this subject Pro- 

 fessor Poggendorff observes, that were the office of the copper 

 plate that of a mere conductor, it should follow that, as copper 

 is the best conductor of electricity, a cu'cle of copper and zinc 

 should form the most powerful battery, and platinum and zinc 

 should be much inferior, whereas the direct contraiy is the fact ; 

 for if the conducting poM'er of copper be taken according to 

 Davy's estimate at 100, that of platinum will be but 16i. 



To the argument of Poggendorff I may add, that if the copper 

 plate in the series acted as a mere conductor, a stout wii-e of 

 copper should answer as w'ell; which is so far from being the 

 case, that in Wollaston's battery the power is gi'eatly increased 

 by the adoption of a plate of copper double the size of what is 

 commonly used. The copper is folded round the zinc ; but that 

 this is not the cause of the increased energy of the batterj', is 

 showTi by the expeiiments of Mr. Binks. This gentleman also 

 proves, that an increase of the copper beyond Wollaston's double 

 plate is accompanied by a still greater display of power*. 



There are some facts connected vnth. the decomposition of 

 chemical compoimds by common electricity which seem still 

 fiuther to dissociate that agent from the voltaic. Several 

 eminent authorities have expressed their conviction, that che- 

 mical and electric attraction are different exhibitions of the same 

 power. This opinion, first promulgated by Volta, was adopted 

 and amplified by Sir H. Da\y, and has been accredited by 

 Faraday, Berzelius, Ampere and others, with more or less mo- 

 dification. Before I proceed to my argument, it may be remarked 

 that this doctrine leads to some speculations which do not appear 

 to correspond mth notions tacitly admitted, or at least not ques- 

 tioned by these philosophers. An electric machine wdll emit 

 sparks twelve or twenty inches long. Are these to be consi- 

 dei-ed sparks of affinity ? can a flash of lightning be otherwise 

 named a flash of affinity ? and what is the stream of light into 

 which a spark passed through the Torricellian vacuum resolves 

 * Phil. Mag. vol. xi. New Series, p. 75. 



