gravitative, may depend upon the same cause.' It is perfectly true, that such vague opinions, though arising from that tendency to generalize which is the essence of science, are of no value except so far as they are both rendered intelligible, and confirmed by experimental research. [Note 9\5: _Phil. Trans._ 1826, p. 383.] [Note 10\5: _Phil. Trans._ 1826, p. 389.] [Note 11\5: _Ibid._ p. 384.] The phenomena of chemical decomposition by means of the voltaic pile, however, led other persons to views very similar to those of Davy. Thus Grotthus in 1805[12\5] published an hypothesis of the same kind. 'The pile of Volta,' he says, 'is an electrical magnet, of which each element, that is, each pair of plates, has a positive and a negative pole. The consideration of this polarity suggested to me the idea that a similar polarity may come into play between the elementary particles of water when acted upon by the same electrical agent; and I avow that this thought was for me a flash of light.' [Note 12\5: _Ann. Chim._ lxviii. 54.] 6. The thought, however, though thus brought into being, was very far from being as yet freed from vagueness, superfluities, and errours. I have elsewhere noticed[13\5] Faraday's remark on Davy's celebrated Memoir of 1806; that 'the mode of action by which the effects take place is stated very generally, so generally, indeed, that probably a dozen precise schemes of electro-chemical action might be drawn up, differing {378} essentially from each other, yet all agreeing with the statement there given.' When Davy and others proceeded to give a little more definiteness and precision to the statement of their views, they soon introduced into the theory features which it was afterwards found necessary to abandon. Thus[14\5] both Davy, Grotthus, Riffault, and Chompré, ascribed electrical decomposition to the action of the _poles_, and some of them even pretended to assign the proportion in which the force of the pole diminishes as the distance from it increases. Faraday, as I have already stated, showed that the polarity must be considered as residing not only in what had till then been called the _poles_, but at every point of the circuit. He ascribed[15\5] electro-chemical decomposition to internal forces, residing in the _particles_ of the matter under decomposition, not to external forces, exerted by the poles. Hence he shortly afterwards[16\5] proposed to reject the word _poles_ altogether, and to employ instead, the term _electrode_, meaning the doors or passages (of whatever surface formed) by which the decomposed elements pass out. What have been called the _positive_ and _negative_ poles he further termed the _Anode_ and _Cathode_; and he introduced some other changes in nomenclature connected with these. He then, as I have related in the History[17\5], invented the Volta-electrometer, which enabled him to measure the quantity of voltaic action, and this he found to be