663. The surfaces at which, according to common phraseology, the electric current enters and leaves a decomposing body, are most important places of action, and require to be distinguished apart from the poles, with which they are mostly, and the electrodes, with which they are always, in contact. Wishing for a natural standard of electric direction to which I might refer these, expressive of their difference and at the same time free from all theory, I have thought it might be found in the earth. If the magnetism of the earth be due to electric currents passing round it, the latter must be in a constant direction, which, according to present usage of speech, would be from east to west, or, which will strengthen this help to the memory, that in which the sun appears to move. If in any case of electro-decomposition we consider the decomposing body as placed so that the current passing through it shall be in the same direction, and parallel to that supposed to exist in the earth, then the surfaces at which the electricity is passing into and out of the substance would have an invariable reference, and exhibit constantly the same relations of powers. Upon this notion we purpose calling that towards the east the _anode_[A], and that towards the west the _cathode_[B]; and whatever changes may take place in our views of the nature of electricity and electrical action, as they must affect the _natural standard_ referred to, in the same direction, and to an equal amount with any decomposing substances to which these terms may at any time be applied, there seems no reason to expect that they will lead to confusion, or tend in any way to support false views. The _anode_ is therefore that surface at which the electric current, according to our present expression, enters: it is the _negative_ extremity of the decomposing body; is where oxygen, chlorine, acids, &c., are evolved; and is against or opposite the positive electrode. The _cathode_ is that surface at which the current leaves the decomposing body, and is its _positive_ extremity; the combustible bodies, metals, alkalies, and bases, are evolved there, and it is in contact with the negative electrode. [A] [Greek: ano] _upwards_, and [Greek: -odos] _a way_; the way which the sun rises. [B] [Greek: kata] _downwards_, and [Greek: -odos] _a way_; the way which the sun sets.