Yet, how difficult it is to avoid substituting the sign for the thing; how difficult to keep the essential quality still living before us, and not to kill it with the word. With all this, we are exposed in modern times to a still greater danger by adopting expressions and terminologies from all branches of knowledge and science to embody our views of simple nature. Astronomy, cosmology, geology, natural history, nay religion and mysticism, are called in in aid; and how often do we not find a general idea and an elementary state rather hidden and obscured than elucidated and brought nearer to us by the employment of terms, the application of which is strictly specific and secondary. We are quite aware of the necessity which led to the introduction and general adoption of such a language, we also know that it has become in a certain sense indispensable; but it is only a moderate, unpretending recourse to it, with an internal conviction of its fitness, that can recommend it.
After all, the most desirable principle would be that writers should borrow the expressions employed to describe the details of a given province of investigation from the province itself; treating the simplest phenomenon as an elementary formula, and deriving and developing the more complicated designations from this.
The necessity and suitableness of such a conventional language where the elementary sign expresses the appearance itself, has been duly appreciated by extending, for instance, the application of the term polarity, which is borrowed from the magnet to electricity, &c. The plus and minus which may be substituted for this, have found as suitable an application to many phenomena; even the musician, probably without troubling himself about these other departments, has been naturally led to express the leading difference in the modes of melody by major and minor.
For ourselves we have long wished to introduce the term polarity into the doctrine of colours; with what right and in what sense, the present work may show. Perhaps we may hereafter find room to connect the elementary phenomena together according to our mode, by a similar use of symbolical terms, terms which must at all times convey the directly corresponding idea; we shall thus render more explicit what has been here only alluded to generally, and perhaps too vaguely expressed.