4. _Voltaic Electricity._--Such is the case in Franklinic electricity,--that which is excited by the common electrical machine. In studying Voltaic electricity, we are led to the conviction that the fluid which is in a condition of momentary _equilibrium_ in electrized conductors, exists in the state of a _Current_ in the voltaic circuit. And here we find polar relations of a new kind existing among the forces. Two voltaic Currents _attract_ each other when they are moving in the _same_, and _repel_ each other when they are moving in _opposite_, directions. But we find, in addition to these, other polar relations of a more abstruse kind, and which the supposition of two fluids does not so readily explain. For instance, if such fluids existed, distinct from each other, it might be expected that it would be possible to exhibit one of them separate from the other. Yet in all the phenomena of electromotive currents, we attempt in vain to obtain one kind of electricity separately. 'I have not,' says Mr. Faraday[2\5], 'been able to find a {363} single fact which could be adduced to prove the theory of two electricities rather than one, in electric currents; or, admitting the hypothesis of two electricities, have I been able to perceive the slightest grounds that one electricity can be more powerful than the other, or that it can be present without the other, or that it can be varied or in the slightest degree affected without a corresponding variation in the other.' 'Thus,' he adds, 'the polar character of the powers is rigorous and complete.' Thus, we too may remark, all the superfluous and precarious parts gradually drop off from the hypothesis which we devise in order to represent polar phenomena; and the abstract notion of Polarity--of equal and opposite powers called into existence by a common condition--remains unincumbered with extraneous machinery. [Note 2\5: _Researches_, 516.]