To this subject he returned in 1834; an intervening memoir--the sixth--being taken up with the power of metals and solids to bring about the combination of gaseous bodies. In the seventh series, published in January, 1834, his first work is to explain the new terms which he has adopted, on the advice of Whewell, to express the facts. The so-called poles, being in his view merely doors or ways by which the current passes, he now terms _electrodes_, distinguishing the entrance and exit respectively as _anode_ and _cathode_,[42] while the decomposable liquid is termed an _electrolyte_, and the decomposing process _electrolysis_. “Finally,” he says, in a passage (here italicised) worthy to be engraved in gold for the essential truth it enunciates on a question of terminology, “I require a term to express those bodies which can pass to the _electrodes_, or, as they are usually called, the poles. Substances are frequently spoken of as being _electronegative_, or _electropositive_, according as they go under the supposed influence of a direct attraction to the positive or negative pole. But these terms are much too significant for the use to which I should have to put them; _for though the meanings are perhaps right, they are only hypothetical, and may be wrong; and then, through a very imperceptible but still very dangerous, because continual, influence, they do great injury to science, by contracting and limiting the habitual views of those engaged in pursuing it_. I propose to distinguish such bodies by calling those _anions_ which go to the anode of the decomposing body; and those passing to the _cathode_, _cations_; and when I shall have occasion to speak of these together, I shall call them _ions_.[43] Thus, the chloride of lead is an _electrolyte_, and when _electrolyzed_ evolves the two _ions_, chlorine and lead, the former being an _anion_ and the latter a _cation_.” In Faraday’s own bound volume of the “Experimental Researches” he has illustrated these terms by the sketch here reproduced. (Fig. 12.) Faraday’s letter to Whewell when he consulted him as to the new words has not been preserved. He discarded, when the paper was printed, the terms he had first used. Whewell’s replies of April 25th and May 5th, 1834, have been preserved and are printed in Todhunter’s biography of Whewell. From the later of the two the following passage is extracted:-- [Sidenote: NEW NOMENCLATURE.] [_Whewell to Faraday_], May 5, 1834.