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



If, then, the current consist of positive and negative electricity, 

 equal to each other in amount and force, how does the state re- 

 sulting from this commixture differ from that of the natural 

 equilibrium of electricity, which, in a well-known state of qui- 

 escence, pervades all nature and manifests no properties ? How 

 is this state of quiescence compatible with the idea of a current ? 

 A current of what ? — is it of insensible electricity without mani- 

 fest properties, neither positive nor negative ? If so^ how is its 

 presence recognised ? The existence of a thing is known by its 

 jjropcrties; if there be no properties, the thing contemplated 

 exists only in imagination. 



The nature of the current is explained by Faraday as follows : — 

 "By current I mean any thing progi-essivc, whether it be a 

 fluid of electricity, or two fluids moving in opposite directions, 

 or merely vibrations, or speaking more genei'ally progressive 

 forces*." Supposing the current for the present to consist in 

 vibrations, it seems very difficult to associate in the mind the two 

 conditions assumed to be compatible, viz. vibrations of solid, 

 rigid mattert, along with progressive forces. Were electricity 

 assumed to be a fluid, a cmTent or progressive force is conceivable, 

 or two such ; but if there be no fluid, the idea of a force which 

 progresses or moves forward is difficult to comprehend ; and in 

 that case, what is it that constitutes the current ? what flows in 

 it ? can vabrations of the particles of an electrified substance be 

 permanently progressive during the whole period in which the 

 electric state is maintained ? The vibrations of all the consti- 

 tuent particles of an electrified mass being once established, they 

 may continue ; but can they be progressive, especially in opposite 

 directions ? For my own part I do not conceive the meaning 

 of the expression " progression of permanent vibrations of fixed 

 particles," for the current I'csolves itself into this : and is the 

 idea of a current included in the expres^sion of it, when it is at 

 the same time declared that probably nothing flows ? I by no 

 means intend to insinuate any doubts concerning the assumption 

 of vibrations amongst the constituent particles of rigid matter : 

 the theory of Boscovich relative to the constitution of solids, pro 

 vides for the possibility of such. Professor Faraday, without ad- 

 mitting or rejecting the doctrine of two fluids, or one fluid, or 

 none, or vibrations of the subjective matter, endeavours to har- 

 monize the idea of a current of progressive forces with all these 

 contingent opinions. But if we abstract from all consideration 

 of fluids and vibrations, it strikes me that "progressive forces" 



* Researches, par. 283. 



t This is the sense in which Faraday intends " vibrations" to be taken. 

 Ibid. 1667. 



