feeling. Combinations of sensations or feelings may always be described, if we have a name for each of the elementary feelings which compose them; but brevity of description, and clearness (which often depends very much on brevity), are greatly promoted by giving distinctive names not to the elements alone, but also to all combinations which are of frequent recurrence. On this occasion I can not do better than quote from Dr. Whewell(222) some of the excellent remarks which he has made on this important branch of our subject.
"The meaning of [descriptive] technical terms can be fixed in the first instance only by convention, and can be made intelligible only by presenting to the senses that which the terms are to signify. The knowledge of a color by its name can only be taught through the eye. No description can convey to a hearer what we mean by apple-green or French gray. It might, perhaps, be supposed that, in the first example, the term apple, referring to so familiar an object, sufficiently suggests the color intended. But it may easily be seen that this is not true; for apples are of many different hues of green, and it is only by a conventional selection that we can appropriate the term to one special shade. When this appropriation is once made, the term refers to the sensation, and not to the parts of the term; for these enter into the compound merely as a help to the memory, whether the suggestion be a natural connection as in 'apple-green,' or a casual one as in 'French gray.' In order to derive due advantage from technical terms of the kind, they must be associated immediately with the perception to which they belong; and not connected with it through the vague usages of common language. The memory must retain the sensation; and the technical word must be understood as directly as the most familiar word, and more distinctly. When we find such terms as tin-white or pinchbeck-brown, the metallic color so denoted ought to start up in our memory without delay or search.
"This, which it is most important to recollect with respect to the simpler properties of bodies, as color and form, is no less true with respect to more compound notions. In all cases the term is fixed to a peculiar meaning by convention; and the student, in order to use the word, must be completely familiar with the convention, so that he has no need to frame conjectures from the word itself. Such conjectures would always be insecure, and often erroneous. Thus the term papilionaceous applied to a flower is employed to indicate, not only a resemblance to a butterfly, but a resemblance arising from five petals of a certain-peculiar shape and arrangement; and even if the resemblance were much stronger than it is in such cases, yet, if it were produced in a different way, as, for example, by one petal, or two only, instead of a 'standard,' two 'wings,' and a 'keel' consisting of two parts more or less united into one, we should be no longer justified in speaking of it as a 'papilionaceous' flower."
When, however, the thing named is, as in this last case, a combination of simple sensations, it is not necessary, in order to learn the meaning of the word, that the student should refer back to the sensations themselves; it may be communicated to him through the medium of other words; the terms, in short, may be defined. But the names of elementary sensations, or elementary feelings of any sort, can not be defined; nor is there any mode of making their signification known but by making the learner experience the sensation, or referring him, through some known mark, to
