The extension of arbitrary names in scientific terminology is by no means to be encouraged. I may mention a case in which it was very properly avoided. When Mr. Faraday's researches on Voltaic electricity had led him to perceive the great impropriety of the term _poles_, as applied to the apparatus, since the processes have not reference to any opposed points, but to two opposite directions of a path, he very suitably wished to substitute for the phrases _positive pole_ and _negative pole_, two words ending in _ode_, from ὅδος, a way. A person who did not see the value of our present maxim, that descriptive terms should be descriptive in their origin, might have proposed words perfectly arbitrary, as _Alphode_, and _Betode_: or, if he wished to pay a tribute of respect to the discoverers in this department of science, _Galvanode_ and _Voltaode_, But such words would very justly have been rejected by Mr. Faraday, and would hardly have obtained any general currency among men of science. _Zincode_ and _Platinode_, terms derived from the metal which, in one modification of the apparatus, forms what was previously termed the pole, are to be avoided, because in their origin too much is casual; and they are not a good basis for derivative terms. The pole at which the zinc is, is the Anode or Cathode, according as it is associated with different metals. Either the _Zincode_ must sometimes mean the pole at which the Zinc is, and at other times that at which the Zinc is not, or else we must have as many names for poles as there are metals. _Anode_ and _Cathode_, the terms which Mr. Faraday adopted, were free from these objections; for they refer to a natural standard of the direction of the voltaic current, in a manner which, though perhaps not obvious at first sight, is easily understood and {314} retained. _An_ode and _Cath_ode, the _rising_ and the _setting_ way, are the directions which correspond to east and west in that voltaic current to which we must ascribe terrestrial magnetism. And with these words it was easy to connect _Anïon_ and _Cathïon_, to designate the opposite elements which are separated and liberated at the two _Electrodes_. APHORISM XIX. _The meaning of Technical Terms must be fixed by convention, not by casual reference to the ordinary meaning of words._