their connexion. As to the existence of our thoughts, we have the evidence of consciousness; a kind of evidence that never was called in question. But as to the existence of vibrations, in the medullary substance of the nerves and brain, no proof has yet been brought.

All therefore we have to expect from this hypothesis, is, that, in vibrations considered abstractly, there should be a variety in kind and degree, which tallies so exactly with the varieties of the thoughts they are to account for, as may lead us to suspect some connexion between the one and the other. If the divisions and subdivisions of thought be found to run parallel with the divisions and subdivisions of vibrations, this would give that kind of plausibility to the hypothesis of their connexion, which we commonly expect even in a mere hypothesis; but we do not find even this.

For, to omit all those thoughts and operations which the author comprehends under the name of ideas, and which he thinks are connected with vibratiuncles; to omit the perception of external objects, which he comprehends under the name of sensations; to omit the sensations, properly so called, which accompany our passions and affections; and to confine ourselves to the sensations which we have by means of our external senses, we can perceive no correspondence between the variety we find in their kinds and degrees, and that which may be supposed in vibrations.

We have five senses, whose sensations differ totally in kind. By each of these, excepting perhaps that of hearing, we may have a variety of sensations, which differ specifically, and not in degree only. How many tastes and smells are there which are specifically different, each of them capable of all degrees of strength and weakness? Heat and cold, roughness and smoothness, hardness and softness, pain and pleasure, are sensations of touch that differ in kind, and each has an endless variety of degrees. Sounds have the qualities of acute and grave, loud and low, with all different degrees of each. The varieties of colour are many more than we have names to express. How shall we find varieties in vibrations corresponding to all this variety of sensations which we have by our five senses only?

I know two qualities of vibrations in an uniform elastic medium, and I know no more. They may be quick or slow in various degrees, and they may be strong or weak in various degrees; but I cannot find any division of our sensations, that will make them tally with those divisions of vibrations. If we had no other sensations but those of hearing, the theory would answer well; for sounds are either acute or grave, which may answer to quick or slow vibration; or they are loud or soft, which answer to strong or weak vibrations. But then we have no variety of vibrations corresponding to the immense variety of sensations which we have by sight, smell, taste, and touch.

Dr. Hartley has endeavoured to find out other two qualities of vibrations to wit, that they may primarily affect one part of the brain or another, and that they may vary in their direction, according as they enter by different external nerves; but these seem to be added to make a number: for, as far as we know, vibrations in an uniform elastic substance, spread over the whole, and in all directions. However, that we may be liberal, we shall grant him four different kinds of vibrations, each of them having as many degrees as he pleases. Can he or any man reduce all our sensations to four kinds? We have five senses, and by each of them a variety of sensations, more than sufficient to exhaust all the varieties we are able to conceive in vibrations.

Dr. Hartley, indeed, was sensible of the difficulty of finding vibrations to suit all the variety of our sensations. His extensive knowledge of physiology and pathology could yield him but a feeble aid; and therefore he is often reduced to the necessity of heaping supposition upon supposition, conjecture upon conjecture, to give some credibility to his hypothesis; and, in seeking out vibrations which may correspond with the sensations of one sense, he seems to forget that those must be omitted which have been appropriated to another.

Philosophers have accounted in some degree for our various sensations of sound, by the vibrations of elastic air. But it is to be observed, first, That we know that such vibrations do really exist; and secondly, That they tally exactly with the most remarkable phenomena of sound. We cannot, indeed, show how any vibration should produce the sensation of sound. This must be resolved into the will of God, or into some cause altogether unknown. But we know, that as the vibration is strong or weak, the sound is loud or low. We know, that as the vibration is quick or slow, the sound is acute or grave. We can point out that relation of synchronous vibrations which produces harmony or discord, and that relation of successive vibrations which produces melody and all this is not conjectured, but proved by sufficient induction. This account of sounds, therefore, is philosophical; although, perhaps, there may be many things relating to sound that we cannot account for, and of which the causes remain latent. The connexions described in this branch of philosophy are the work of God, and not the fancy of men.

If any thing similar to this could be shown in accounting for all our sensations by vibrations in the medullary substance of the nerves and brain, it would deserve a place in sound philosophy. But, when we are told of vibrations in a substance, which no man could ever prove to have vibrations, or to be capable of them; when such imaginary vibrations are brought to account for all our sensations, though we can perceive no correspondence in their variety of kind and degree, to the variety of sensations, the connexions described in such a system, are the creatures of human imagination, not the work of God.

The rays of light make an impression upon the optic nerves; but they make none upon the auditory or olfactory. The vibrations of the air make an impression upon the auditory nerves: but none upon the optic or the olfactory. The effluvia of bodies make an impression upon the olfactory nerves but make none upon the optic or auditory. No man has been able to give a shadow of reason for this. While this is the case, is it not better to confess our ignorance of the nature of those impressions made upon the nerves and brain in perception, than to flatter our pride with the conceit of knowledge which we have not, and to adulterate philosophy with the spurious brood of hypotheses?

CHAPTER IV.

FALSE CONCLUSIONS DRAWN FROM THE IMPRESSIONS BEFORE MEN

TIONED.

SOME philosophers among the ancients, as well as among the moderns, imagined that man is nothing but a piece of matter, so curiously organized that the impressions of external objects produce in it sensation, perception, remembrance, and all the other operations we are conscious of. This foolish

opinion could only take its rise from observing the constant connexion which the Author of nature hath established between certain impressions made upon our senses, and our perception of the objects by which the impression is made; from which they weakly inferred, that those impressions were the proper efficient causes of the corresponding perception.

But no reasoning is more fallacious than this, that because two things are always conjoined, therefore one must be the cause of the other. Day and night have been joined in a constant succession since the beginning of the world; but who is so foolish as to conclude from this, that day is the cause of night, or night the cause of the following day? There is indeed nothing more ridiculous than to imagine that any motion or modification of matter should produce thought.

If one should tell of a telescope so exactly made as to have the power of seeing; of a whispering gallery that had the power of hearing; of a cabinet so nicely framed as to have the power of memory; or of a machine so delicate as to feel pain when it was touched; such absurdities are so shocking to common sense that they would not find belief even among savages; yet it is the same absurdity to think, that the impressions of external objects upon the machine of our bodies, can be the real efficient cause of thought and perception.

Passing this therefore as a notion too absurd to admit of reasoning; another conclusion very generally made by philosophers, is, that in perception an impression is made upon the mind as well as upon the organ, nerves, and brain. Aristotle, as was before observed, thought that the form or image of the object perceived, enters by the organ of sense, and strikes upon the mind. Mr. Hume gives the name of impressions to all our perceptions, to all our sensations, and even to the objects which we perceive. Mr. Locke affirms very positively, that the ideas of external objects are produced in our minds by impulse, "that being the only way we can conceive bodies to operate in." It ought, however, to be observed, in justice to Mr. Locke, that he retracted this notion in his first letter to the Bishop of Worcester, and promised, in the next edition of his Essay, to have that passage rectified; but either from forgetfulness in the author, or negligence in the printer, the passage remains in all the subsequent editions I have seen.

There is no prejudice more natural to man, than to conceive of the mind as having some similitude to body in its operations. Hence, men have been prone to imagine, that as bodies are put in motion by some impulse or impression made upon them by contiguous bodies; so the mind is made to think and to perceive by some impression made upon it, or some impulse given to it by contiguous objects. If we have such a notion of the mind as Homer had of his gods, who might be bruised or wounded with swords and spears, we may then understand what is meant by impressions made upon it by a body: but if we conceive the mind to be immaterial, of which I think we have very strong proofs, we shall find it difficult to affix a meaning to impressions made upon it.

There is a figurative meaning of impressions on the mind which is well authorised, and of which we took notice in the observations made on that word; but this meaning applies only to objects that are interesting. To say that an object which I see with perfect indifference makes an impression upon my mind, is not, as I apprehend, good English. If philosophers mean no more but that I see the object, why should they invent an improper phrase to express what every man knows how to express in plain English?

But it is evident, from the manner in which this phrase is used by

modern philosophers, that they mean not barely to express by it, my perceiving an object, but to explain the manner of perception. They think that the object perceived acts upon the mind, in some way similar to that in which one body acts upon another, by making an impression upon it. The impression upon the mind is conceived to be something wherein the mind is altogether passive, and has some effect produced in it by the object. But this is a hypothesis which contradicts the common sense of mankind, and which ought not to be admitted without proof.

That

When I look upon the wall of my room, the wall does not act at all, nor is capable of acting; the perceiving it is an act or operation in me. this is the common apprehension of mankind with regard to perception, is evident from the manner of expressing it in all languages.

The vulgar give themselves no trouble how they perceive objects; they express what they are conscious of, and they express it with propriety; but philosophers have an avidity to know how we perceive objects; and conceiving some similitude between a body that is put in motion, and a mind that is made to perceive, they are led to think, that as the body must receive some impulse to make it move, so the mind must receive some impulse or impression to make it perceive. This analogy seems to be confirmed, by observing that we perceive objects only when they make some impression upon the organs of sense, and upon the nerves and brain ; but it ought to be observed, that such is the nature of body that it cannot change its state, but by some force impressed upon it. This is not the nature of mind. All that we know about it shows it to be in its nature living and active, and to have the power of perception in its constitution, but still within those limits to which it is confined by the laws of Nature.

appears, therefore, that this phrase of the mind's having impressions made upon it by corporeal objects in perception, is either a phrase without any distinct meaning, and contrary to the propriety of the English language, or it is grounded upon a hypothesis which is destitute of proof. On that account, though we grant that in perception there is an impression made upon the organ of sense, and upon the nerves and brain, we do not admit that the object makes any impression upon the mind.

There is another conclusion drawn from the impressions made upon the brain in perception, which I conceive to have no solid foundation, though it has been adopted very generally by philosophers. It is, that, by the impressions made on the brain, images are formed of the object perceived; and that the mind, being seated in the brain, as its chamber of presence, immediately perceives those images only, and has no perception of the external object but by them. This notion of our perceiving external objects, not immediately, but in certain images or species of them conveyed by the senses, seems to be the most ancient philosophical hypothesis we have on the subject of perception, and to have, witli small variations, retained its authority to this day.

Aristotle, as was before observed, maintained, that the species, images, or forms of external objects, coming from the object, are impressed on the mind. The followers of Democritus and Epicurus held the same thing, with regard to slender films of subtile matter coming from the object, that Aristotle did with regard to his immaterial species or forms.

Aristotle thought every object of human understanding enters at first by the senses; and that the notions got by them are by the powers of the mind refined and spiritualized, so as at last to become objects of the most sublime and abstracted sciences. Plato, on the other hand, had a very mean opinion of all the knowledge we get by the senses. He thought it did not deserve the name of knowledge, and could not be the foundation

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of science; because the objects of sense are individuals only, and are in a constant fluctuation. All science, according to him, must be employed about those eternal and immutable ideas, which existed before the objects of sense, and are not liable to any change. In this there was an essential difference between the systems of these two philosophers. The notion of eternal and immutable ideas, which Plato borrowed from the Pythagorean school, was totally rejected by Aristotle, who held it as a maxim, that there is nothing in the intellect which was not at first in the senses.

But notwithstanding this great difference in those two ancient systems, they might both agree as to the manner in which we perceive objects by our senses and that they did so, I think, is probable; because Aristotle, as far as I know, neither takes notice of any difference between himself and his master upon this point, nor lays claim to his theory of the manner of our perceiving objects as his own invention. It is still more probable from the hints which Plato gives in the seventh book of his Republic, concerning the manner in which we perceive the objects of sense; which he compares to persons in a deep and dark cave, who see not external objects themselves, but only their shadows, by a light into the cave through a small opening.

It seems therefore probable, that the Pythagoreans and Platonists agreed with the Peripatetics in this general theory of perception; to wit, that the objects of sense are perceived only by certain images, or shadows of them, let into the mind, as into a camera obscura.

The notions of the ancients were very various with regard to the seat of the soul. Since it has been discovered, by the improvements in anatomy, that the nerves are the instruments of perception, and of the sensations accompanying it, and that the nerves ultimately terminate in the brain, it has been the general opinion of philosophers that the brain is the seat of the soul; and that she perceives the images that are brought there, and external things only by means of them.

Des Cartes, observing that the pineal gland is the only part of the brain that is single, all the other parts being double, and thinking that the soul must have one seat, was determined by this to make that gland the soul's habitation, to which, by means of the animal spirits, intelligence is brought of all objects that affect the senses.

Others have not thought proper to confine the habitation of the soul to the pineal gland, but to the brain in general, or to some part of it, which they call the sensorium. Even the great Newton favoured this opinion, though he proposes it only as a query, with that modesty which distinguished him no less than his great genius. "Is not," says he, "the sensorium of animals the place where the sentient substance is present, and to which the sensible species of things are brought through the nerves and brain, that there they may be perceived by the mind present in that place? And is there not an incorporeal, living, intelligent, and omnipresent Being, who, in infinite space, as if it were in his sensorium, intimately perceives things themselves, and comprehends them perfectly, as being present to them; of which things, that principle in us, which perceives and thinks, discerns only, in its little sensorium, the images brought to it through the organs of the senses?"

His friend Dr. Samuel Clarke adopted the same sentiment with more confidence. In his papers to Leibnitz, we find the following passages: "Without being present to the images of the things perceived, it (the soul) could not possibly perceive them. A living substance can only there perceive where it is present, either to the things themselves, (as the omnipresent God is to the whole universe), or to the images of things, (as the