give a history of the notion which we form of it. Taking it for granted that every one knows what is meant when we use that term, we merely assert here, that for some cause or other it is exceedingly difficult to think of it except in the light of a modification of EXTENSION. The correctness of this remark may not, perhaps, appear perfectly obvious at first; but the expressions which we apply to intervals of duration are an evidence of its truth.

We say before such a time or after such a time, the same as before or after any material object; we speak of a long or short time with no more hesitation than of a long or short distance, of a long or short bridge, or railway, or any other object of extension: We utter ourselves precisely in the same way we should do if we were certain of having detected some real analogy between the two, between length and shortness in material substances, and what are called length and shortness in time. But it is not too much to say that there is no such analogy, no such similitude; nor is it worth while to anticipate that we shall ever be able to detect such analogy or similitude until we can in practice apply the measures of feet, ells, roods, &c., to hours, and days, and weeks.. How then can it be accounted for, that we apply terms nearly in the same way as if this were the case, and as if such measurements could be made?

To this inquiry we are not prepared to return an answer which we can assert to be entirely satisfactory. It is probably only another instance of that early and strong habit which we have all formed, of transferring in our thoughts the material to the immaterial, and of contemplating what is abstract and invisible in the light of what is seen and tangible. Mr. Stewart, however, is more definite in his explanation. He suggests that the strong association of these ideas has most probably arisen in this manner, viz., from our constantly measuring one of these quantities by the other. It is the common method, as is well known, to measure time by motion, and motion is

measured by extension. In an hour the hand of a clock moves over a certain space; in two hours over double the space, and so on. And in this way he supposes we may have been gradually led to associate so strongly with the idea of time a conception analogous to that of visible and material length.

No doubt it is convenient to apply the terms "long" and "short," "before" and "after," and others similar, to Time. We could not well dispense with them. But it ought to be remembered, if we would have a right notion of things, that the application of those expressions has arisen either from the mode in which we measure time, or from some other accidental grounds of association; and that time and extension are essentially distinct in their nature.

§ 236. Of high and low notes in music.

We speak of high and low in reference to notes in music, the same as of the high or low position of material bodies. There is supposed to be some analogy between the relation which the notes in the scale of music bear to each other, and the relation of superiority and inferiority in the position of bodies of matter. But it is impossible to prove the existence of such analogy, however generally it may have been supposed; and the supposition itself of its existence has no doubt arisen from a casual association of ideas, which has acquired strength by lapse of time and by repetition.

A proof of this association of ideas being purely accidental is, that an association the very reverse of this was once prevalent. It is remarked in the preface to Gregory's edition of Euclid's works, that the more ancient Greek writers considered the grave sounds as high, and the acute ones as low. The present mode of speaking on the subject is of more recent origin; but at what time and in what way it was introduced cannot be asserted with confidence. In the preface just referred to, it is, however, observed, that the ancient Greek custom of looking upon the grave

sounds as high and the acute as low, precisely the reverse of what is now common, continued down until the time of Boethius. It has been conjectured with some ingenuity, that this connexion or association of thought among the Greeks and Romans, for it was equally prevalent among both, might have been owing to the construction of their musical instruments. The string which sounded the grave, or what we call the low tone, it has been supposed, was placed highest, and that which gave the shrill or acute had the lowest place. If this conjecture could be ascertained to be well founded, it would strikingly show from what very slight causes strong and permanent associations often arise. It is hardly necessary to observe, that it is important to examine the origin and progress of such associations, in order that we may correct those erroneous and illusive notions which will be found to be built upon them.*

§ 237. Connexion of the ideas of extension and colour.

There is no necessary connexion between colour, as the term is commonly employed by philosophers, and extension. The word COLOUR, in its interior or psychical application, properly denotes a sensation in the mind; the word EXTENSION, the quality of an external, material object. There is, therefore, no more natural connexion, and no more analogy between the two, than there is between pain and solidity. And yet it so happens that we never have the sensation or idea of colour without at the same time associating extension with it; we find them, however different they may be in their nature, inseparable in our thoughts. This

*It is not necessary, for any purpose we have in view, here to trace the origin of the association; but it is undoubtedly the fact, that we almost invariably attribute the notion of highness or loftiness to those who excel, or are particularly favored in any respects. We can hardly think of a nobleman, prince, or king, without creating for them an imaginary orbit somewhere in the upper sky, where they revolve far above the heads of ordinary mortals. Hence the expressions High rank, High birth, Elevated genius, Superior talents, &c., and their opposites, Low rank, Inferior genius, and the like.-(See Stewart's Essays, ii., ch. iii. Kames's Criticism, part vii., ch. iv.)

strong association is formed in consequence of our always perceiving extension at the very time in which the sensation of colour is excited in the mind. The perception of the one and the sensation of the other have been so long simultaneous, that we have been gradually drawn into the belief that, on the one hand, all colour has extension, and on the other, all extension has colour. But what we call colour being, in its subjective experience, merely a state of the mind, it is not possible that it should with propriety be predicated of any external, material substances. Nor is it less evident, if colour be merely a sensation or state of the mind, that matter can exist and does exist without it.

But what has been said will not satisfy all the queries which may be started on this point, unless we remark also on the ambiguity in the word COLOUR. The view which has been taken of the connexion between colour and extension is founded on the supposition that color denotes a sensation of the mind, and that merely. It is maintained by some writers, and not without some reason for their opinion, that the word colour has two meanings, and that it is thus generally understood: (1.) It denotes that disposition, or arrangement, or whatever it may be, in the particles of matter, which not only cause the rays of light to be reflected, but to be reflected in different ways; (2.) It denotes that mental sensation which follows when the rays have reached the retina of the eye. When people use the term with this diversity of signification, they can say with truth that external bodies have colour, and also that colour is a sensation of the mind. It may be said also, in the first sense of the term which has been mentioned, that colour has extension, because particles of matter have extension.

§ 238. Tendency of the mind to pass from the sign to the thing

signified.

Mr. Stewart gives a reason for our inattention to the internal sensation of colour (or colour considered

as an affection of the mind), which is worthy of some notice. The principle, it will be observed, is a general one, applicable to other cases as well as this."It is well known," he says, " to be a general law of our constitution, when one thing is destined, either by nature or by convention, to be the sign of another, that the mind has a disposition to pass on as rapidly as possible to the thing signified, without dwelling on the sign as an object worthy of its attention. The most remarkable of all examples of this occurs in the acquired perceptions of sight, where our estimates of distance are frequently the result of an intellectual process, comparing a variety of different signs together, without a possibility on our part, the moment afterward, of recalling one single step of the process to our recollection. Our inattention to the sensations of colour, considered as affections of the Mind or as modifications of our own being, appears to me to be a fact of precisely the same description; for all these sensations were plainly intended by nature to perform the offices of signs, indicating to us the figures and distances of things external. Of their essential importance in this point of view, an idea may be formed by supposing for a moment the whole face of nature to exhibit only one uniform colour, without the slightest variety even of light and shade. Is it not selfevident, that, on this supposition, the organ of sight would be entirely useless, inasmuch as it is by the varieties of colour alone that the outlines or visible figures of bodies are so defined as to be distinguishable one from another? Nor could the eye in this case give us any information concerning diversities of distance; for all the various signs of it enumerated by optical writers presuppose the antecedent recognition of the bodies around us as separate objects of perception. It is not, therefore, surprising, that signs so indispensably subservient to the exercise of our noblest sense should cease in early infancy to attract notice as the subjects of our consciousness, and that afterward they should present themselves to the Imagina