application of a not inconsiderable number of old words to new uses. Whenever any branch of knowledge, any art or science, either originates or is extended and perfected, the natural impulse is always to subserve its new uses with our old phraseology. The new classifications, substances, processes, products are not so unlike those already familiar to us that they may not be largely called by the same names, without fear of obscurity or error. Every technical vocabulary is thus made up to no small extent of the terms of common life, more precisely or more pregnantly used. The botanist talks of leaves and flowers; but in either term he includes some things that the common man would exclude, and the contrary. Current, conductor, induction, in the mouth of the electrician, mean things of which he who knows nothing of physics has no conception. Many a man who is aware that cohere means 'stick together' would be at a loss to distinguish cohesion from adhesion. Atom, base, acid, salt, affinity, reaction, are but instances of the words innumerable to which the chemist has given a new and special significance. In fact, the whole apparatus of common speech, as applied to the more definite and sharply distinguished uses of science, undergoes a kind of working-over and adaptation, which is of every degree, from such a conscious and artificial application as that of the word salt, used to express a large class of chemical compounds regarded as analogous with the substance formerly called by that name, down to such simple limitation or distincter apprehension of the true force of a term as is hardly separable from that change of implication without change of identity which we have illustrated above, by reference to the words sun, heat, rise and fall, etc. The mode of linguistic growth which we are now considering does, indeed, shade off into the former one, and is most nearly akin with it, in nature and in necessity. No language can possibly lose the capacity for it without losing its very life; in some languages, as we shall see hereafter, it is compelled to do the whole work of linguistic adaptation, external growth being a thing unknown.
In our own tongue, however, external growth, as represented by the formation of new derivatives, and new combin-
