wards the painful feeling; and, to speak in the common language of mankind, he feels nothing in the stone, but feels a violent pain in his head. It is quite otherwise when he leans his head gently against the pillar; for then he will tell you that he feels nothing in his head, but feels hardness in the stone. Hath he not a sensation in this case as well as in the other? Undoubtedly he hath; but it is a sensation which nature intended only as a sign of something in the stone; and, accordingly, he instantly fixes his attention upon the thing signified; and cannot, without great difficulty, attend so much to the sensation as to be persuaded that there is any such thing distinct from the hardness it signifies.

"But however difficult it may be to attend to this fugitive sensation, to stop its rapid progress, and to disjoin it from the external quality of hardness, in whose shadow it is apt immediately to hide itself: this is what a philosopher by pains and practice must attain, otherwise it will be impossible for him to reason justly upon this subject, or even to understand what is here advanced. For the last appeal, in subjects of this nature, must be to what a man feels and perceives in his own mind."

§ 31. Of certain indefinite feelings sometimes ascribed to the touch. In connexion with these views on the sensations of touch, it is proper to remark, that certain feelings have been ascribed to that sense, which are probably of a character too indefinite to admit of a positive and undoubted classification. Although they clearly have their place in the general arrangement which has been laid down, with the states of mind which we are now considering; that is to say, are rather of an external and material, than of an internal origin; still they do not so evidently admit of an assignment to a particular sense. Those sensations to which we now refer, (if it be proper to use that term in application to them,) appear to have their origin in the human system considered as a whole, made up of bones, flesh, muscles, the senses, &c., rather than to be susceptible of being traced to any particular part. Of this description are the feelings expressed by the terms uneasiness, weariness, weakness, sickness, and those of an opposite character, as ease, hilarity, health, vigour, &c.

Similar views will be found to apply, in part at least, to the sensations which we express by the terms HUNGER and THIRST. These appear to be complex in their nature, including a feeling of uneasiness, combined with a desire to relieve that uneasiness. When we say that these views will apply in part to hunger and thirst, the design is to limit the application of them to the element of uneasiness. This elementary feeling undoubtedly has its origin in the bodily system, and therefore comes in this case under the general class of notions of an EXTERNAL Origin; but still it is not easy to say that it should be arranged with our tactual feelings, which has sometimes been done. Every one must be conscious, it is thought, that the feeling of hunger does not greatly resemble the sensations of hardness and softness, roughness or smoothness, or other sensations which are usually ascribed to the touch.The cause of that peculiar state of the nerves of the stomach, which is antecedent to the uneasy feeling involved in what is termed hunger, has been a subject of difference of opinion, and does not appear to be well understood. If we were fully acquainted with this we might perhaps be less at a loss where to arrange the feeling in question.

32. Relation between the sensation and what is outwardly signified. We here return a moment to the subject of the relation between the internal sensation and the outward object; and again repeat, that the mental state and the corresponding outward object are altogether diverse. This view holds good in the case of the secondary, as well as of the primary qualities of matter. Whether we speak of extension, or resistance, or heat, or colour, or roughness, there are, in all cases alike, two things, the internal affection and the outward quality; but they are utterly distinct, totally without likeness to each other. But how it happens that one thing which is totally different from another can nevertheless give us a knowledge of that from which it differs, it would be a waste of time to attempt to explain. Our knowledge is undoubtedly limited to the mere fact. This is one those of difficult but decisive points in MENTAL PHILOSOPHY, of which it is essential to possess a

precise and correct understanding. The letters which cover over the page of a book are a very different thing from the thought and the combinations of thought which they stand for. The accountant's columns of numerals are not identical with the quantities and their relations which they represent. And so in regard to the mind; all its acts are of one kind, and what they stand for is of another. The mind, in all its feelings and operations, is governed by its own laws, and characterizes its efforts by the essential elements of its own nature. Nothing which is seen or heard, nothing which is the subject of taste, or touch or any other sense, nothing material, which can be imagined to exist in any place or in any form, can furnish the least positive disclosure either of its intrinsic nature or of the mode of its action.

What, then, is the relation between the sensation and the outward object, between the perception and the thing perceived? Evidently that of the sign and the thing signified. And as, in a multitude of cases, the sign may give a knowledge of its objects without any other grounds of such knowledge than mere institution or appointment, so it is in this. The mind, maintaining its appropriate action, and utterly rejecting the intervention of all images and visible representations, except what are outward and material, and totally distinct from itself both in place and nature, is, notwithstanding, susceptible of the knowledge of things exterior, and can form an acquaintance with the universe of matter.

CHAPTER VI.

THE SENSE OF SIGHT.

33. Of the organ of sight, and the uses or benefits of that sense. Of those instruments of external perception with which a benevolent Providence has favoured us, a high rank must be given to the sense of seeing. If we were restricted in the process of acquiring knowledge to the informations of the touch merely, how many embarrassments

would attend our progress, and how slow it would prove! Having never possessed sight, it would be many years before the most acute and active person could form an idea of a mountain or even of a large edifice. But by the additional help of the sense of seeing, he not only observes the figure of large buildings, but is in a moment possessed of all the beauties of a wide and variegated landscape.

The organ of this sense is the eye. On a slight examination, the eye is found to be a sort of telescope, haying its distinct parts, and discovering throughout the most exquisite construction. The medium on which this organ acts are rays of light, everywhere diffused, and always advancing, if they meet with no opposition, in direct lines. The eye, like all the other senses, not only receives externally the medium on which it acts, but carries the rays of light into itself; and on principles purely scientific, refracts and combines them anew.

It does not, however, fall within our plan to give a minute description of the eye, which belongs rather to the physiologist; but such a description, with the statement of the uses of the different parts of the organ, must be, to a candid and reflecting mind, a most powerful argument in proof of the existence and goodness of the Supreme Being How wonderful, among other things, is the adaptation of the rays of light to the eye! If these rays were not of a texture extremely small, they would cause much pain to the organ of vision, into which they so rapidly pass. If they were not capable of exciting within us the sensations of colour, we should be deprived of much of that high satisfaction which we now take in beholding surrounding objects; showing forth, wherever they are to be found, the greatest variety and the utmost richness of tints.

§ 34. Statement of the mode or process in visual perception.

In the process of vision, the rays of light, coming from various objects and in various directions, strike in the first place on the pellucid or transparent part of the ball of the eye.

If they were to continue passing on precisely in the

same direction, they would produce merely one mingled and indistinct expanse of colour. In their In their progress, however, through the crystalline humour, they are refracted or bent from their former direction, and are distributed to certain focal points on the retina, which is a white, fibrous expansion of the optic nerve.

The rays of light, coming from objects in the field of vision, whether it be more or less extensive, as soon as they have been distributed on their distinct portions of the retina, and have formed an image there, are immediately followed by the sensation or perception which is termed sight. The image which is thus pictured on the retina is the last step which we are able to designate in the material part of the process in visual perception; the mental state follows; but it is not in our power to trace, even in the smallest degree, any physical connexion between the optical image and the corresponding state of the mind. All that we can say in this case is, that we suppose them to hold to each other the relation of antecedent and consequent by an ultimate law of our constitution.

35. Of the original and acquired perceptions of sight.

In speaking of those sensations and perceptions, the origin of which is generally attributed to the sense of sight, it is necessary to make a distinction between those which are ORIGINAL and those which are ACQUIRED. Nothing is properly original with the sense of sight but the sensations of colour, such as red, blue, yellow. These sensations (or perceptions, as they are otherwise called, when the internal feeling is combined with a reference to the external cause) are exceedingly numerous. In this respect, the intimations of the sense of sight stand on the same footing with those of taste and hearing; although distinctive names, in consequence of the difficulty of accurately separating and drawing the line between each, are given only in a few cases. All the sensations of colour are original with the sight, and are not to be ascribed to any other sense.

A part, however, of that knowledge, which we attribute to the sight, and which has the appearance of being immediate and original in that sense, is not so. Some of