smell, is acquired. In like manner, we learn all those qualities in bodies, which we call their smell, their taste, their sound. These are all secondary qualities, and we give the same name to them which we give to the sensations they produce; not from any similitude between the sensation and the quality of the same name, but because the quality is signified to us by the sensation as its sign, and because our senses give us no other knowledge of the quality, but that it is fit to produce such a sensation.

By the other two senses, we have much more ample information. By sight, we learn to distinguish objects by their colour, in the same manner as by their sound, taste, and smell. By this sense, we perceive visible objects to have extension in two dimensions, to have visible figure and magnitude, and a certain angular distance from one another. These I conceive are the original perceptions of sight.

By touch, we not only perceive the temperature of bodies as to heat and cold, which are secondary qualities, but we perceive originally their three dimensions, their tangible figure, and magnitude, their linear distance from one another, their hardness, softness, or fluidity. These qualities we originally perceive by touch only; but, by experience, we learn to perceive all or most of them by sight.

We learn to perceive, by one sense, what originally could have been perceived only by another, by finding a connexion between the objects of the different senses. Hence the original perceptions, or the sensations of one sense, become signs of whatever has always been found connected with them; and from the sign the mind passes immediately to the conception and belief of the thing signified: and although the connexion in the mind between the sign, and the thing signified by it, be the effect of custom, this custom becomes a second nature, and it is difficult to distinguish it from the original power of perception.

Thus, if a sphere of one uniform colour be set before me, I perceive evidently by my eye its spherical figure, and its three dimensions. All the world will acknowledge, that by sight only, without touching it, I may be certain that it is a sphere: yet it is no less certain that, by the original power of sight, I could not perceive it to be a sphere, and to have three dimensions. The eye originally could only perceive two dimensions, and a gradual variation of colour on the different sides of the object.

It is experience that teaches me that the variation of colour is an effect of spherical convexity, and of the distribution of light and shade. But so rapid is the progress of the thought, from the effect to the cause, that we attend only to the last, and can hardly be persuaded that we do not immediately see the three dimensions of the sphere.

Nay, it may be observed, that, in this case, the acquired perception in a manner effaces the original one; for the sphere is seen to be of one uniform colour, though originally there would have appeared a gradual variation of colour: but that apparent variation we learn to interpret as the effect of light and shade falling upon a sphere of one uniform colour.

A sphere may be painted upon a plane, so exactly, as to be taken for a real sphere, when the eye is at a proper distance, and in the proper point of view. We say in this case, that the eye is deceived, that the appearance is fallacious: but there is no fallacy in the original perception, but only in that which is acquired by custom. The variation of colour, exhibited to the eye by the painter's art, is the same which nature exhibits by the different degrees of light falling upon the convex surface of a sphere.

In perception, whether original or acquired, there is something which

may be called the sign, and something which is signified to us, or brought to our knowledge by that sign.

In original perception, the signs are the various sensations which are produced by the impressions made upon our organs. The things signified, are the objects perceived in consequence of those sensations, by the original constitution of our nature.

Thus, when I grasp an ivory ball in my hand, I have a certain sensation of touch. Although this sensation be in the mind, and have no similitude to any thing material, yet, by the laws of my constitution, it is immediately followed by the conception and belief, that there is in my hand a hard smooth body of a spherical figure, and about an inch and a half in diameter. This belief is grounded neither upon reasoning, nor upon experience; it is the immediate effect of my constitution, and this I call original perception.

In acquired perception, the sign may be either a sensation, or something originally perceived. The thing signified, is something which, by experience, has been found connected with that sign.

Thus, when the ivory ball is placed before my eye, I perceive by sight what I before perceived by touch, that the ball is smooth, spherical, of such a diameter, and at such a distance from the eye; and to this is added the perception of its colour. All these things I perceive by sight distinctly, and with certainty: yet it is certain, from principles of philosophy, that if I had not been accustomed to compare the informations of sight with those of touch, I should not have perceived these things by sight. I should have perceived a circular object, having its colour gradually more faint towards the shaded side. But I should not have perceived it to have three dimensions, to be spherical, to be of such a linear magnitude, and at such a distance from the eye. That these last mentioned are not original perceptions of sight, but acquired by experience, is sufficiently evident from the principles of optics, and from the art of painters, in painting objects of three dimensions, upon a plane which has only two. And it has been put beyond all doubt, by observations recorded of several persons, who having, by cataracts in their eyes, been deprived of sight from their infancy, have been couched and made to see, after they came to years of understanding.

Those who have had their eye-sight from infancy, acquire such perceptions so early, that they cannot recollect the time when they had them not, and therefore make no distinction between them and their original perceptions; nor can they be easily persuaded, that there is any just foundation for such a distinction. In all languages men speak with equal assurance of their seeing objects to be spherical or cubical, as of their feeling them to be so; nor do they ever dream, that these perceptions of sight were not as early and original as the perceptions they have of the same objects by touch."

This power which we acquire of perceiving things by our senses, which originally we should not have perceived, is not the effect of any reasoning on our part: it is the result of our constitution, and of the situation in which we happen to be placed.

We are so made, that when two things are found to be conjoined in certain circumstances, we are prone to believe that they are connected by nature, and will always be found together in like circumstances. The belief which we are led into in such cases, is not the effect of reasoning, nor does it arise from intuitive evidence in the thing believed; it is, as I apprehend, the immediate effect of our constitution accordingly it is

strongest in infancy, before our reasoning power appears, before we are capable of drawing a conclusion from premises. A child who has once burnt his finger in a candle, from that single instance connects the pain of burning with putting his finger in the candle, and believes that these two things must go together. It is obvious, that this part of our constitution is of very great use before we come to the use of reason, and guards us from a thousand mischiefs, which, without it, we would rush into; it may sometimes lead us into error, but the good effects of it far overbalance the ill.

It is, no doubt, the perfection of a rational being to have no belief but what is grounded on intuitive evidence, or on just reasoning: but man, I apprehend, is not such a being; nor is it the intention of Nature that he should be such a being, in every period of his existence. We come into the world without the exercise of reason; we are merely animal before we are rational creatures; and it is necessary for our preservation, that we should believe many things before we can reason. How then is our belief to be regulated before we have reason to regulate it? has Nature left it to be regulated by chance? By no means. It is regulated by certain principles, which are parts of our constitution; whether they ought to be called animal principles, or instinctive principles, or what name we give to them, is of small moment; but they are certainly different from the faculty of reason: they do the office of reason while it is in its infancy, and must as it were be carried in a nurse's arms, and they are leading-strings to it in its gradual progress.

From what has been said, I think it appears, that our original powers of perceiving objects by our senses receive great improvement by use and habit; and without this improvement, would be altogether insufficient for the purposes of life. The daily occurrences of life not only add to our stock of knowledge, but give additional perceptive powers to our senses; and time gives us the use of our eyes and ears, as well as of our hands and legs.

This is the greatest and most important improvement of our external senses. It is to be found in all men come to years of understanding, but is various in different persons, according to their different occupations, and the different circumstances in which they are placed. Every artist acquires an eye as well as a hand in his own profession: his eye becomes skilled in perceiving, no less than his hand in executing, what belongs to his employment.

Besides this improvement of our senses, which nature produces without our intention, there are various ways in which they may be improved, or their defects remedied by art. As, first, by a due care of the organs of sense; that they be in a sound and natural state. This belongs to the department of the Medical Faculty.

Secondly, By accurate attention to the objects of sense. The effects of such attention in improving our senses appear in every art. The artist, by giving more attention to certain objects than others do, by that means perceives many things in those objects which others do not. Those who happen to be deprived of one sense, frequently supply that defect, in a great degree, by giving more accurate attention to the objects of the senses they have. The blind have often been known to acquire uncommon acuteness in distinguishing things by feeling and hearing; and the deaf are uncommonly quick in reading men's thoughts in their countenance.

A third way in which our senses admit of improvement is, by additional organs or instruments contrived by art. By the invention of optical

glasses, and the gradual improvement of them, the natural power of vision is wonderfully improved, and a vast addition made to the stock of knowledge which we acquire by the eye. By speaking trumpets, and ear trumpets, some improvement has been made in the sense of hearing. Whether by similar inventions the other senses may be improved, seems

uncertain.

A fourth method by which the information got by our senses may be improved, is, by discovering the connexion which nature hath established between the sensible qualities of objects and their more latent qualities.

By the sensible qualities of bodies, I understand those that are perceived immediately by the senses, such as their colour, figure, feeling, sound, taste, smell. The various modifications, and various combinations of these, are innumerable; so that there are hardly two individual bodies in nature that may not be distinguished by their sensible qualities.

The latent qualities are such as are not immediately discovered by our senses; but discovered, sometimes by accident, sometimes by experiment or observation. The most important part of our knowledge of bodies, is the knowledge of the latent qualities of the several species by which they are adapted to certain purposes, either for food, medicine, or agriculture, or for the materials or utensils of some art or manufacture.

I am taught, that certain species of bodies have certain latent qualities; but how shall I know that this individual is of such a species? This must be known by the sensible qualities which characterise the species. I must know that this is bread, and that wine, before I eat the one or drink the other. I must know that this is rhubarb, and that opium, before I use the one or the other for medicine.

It is one branch of human knowledge to know the names of the various species of natural and artificial bodies, and to know the sensible qualities by which they are ascertained to be of such a species, and by which they are distinguished from one another. It is another branch of knowledge to know the latent qualities of the several species, and the uses to which they are subservient.

The man who possesses both the branches, is informed by his senses of innumerable things of real moment, which are hidden from those who possess only one, or neither. This is an improvement in the information got by our senses, which must keep pace with the improvements made in natural history, in natural philosophy, and in the arts.

It would be an improvement still higher, if we were able to discover any connexion between the sensible qualities of bodies and their latent qualities, without knowing the species, or what may have been discovered with regard to it.

Some philosophers of the first rate have made attempts towards this noble improvement, not without promising hopes of success. Thus the celebrated Linnæus has attempted to point out certain sensible qualities by which a plant may very probably be concluded to be poisonous, without knowing its name or species. He has given several other instances, wherein certain medical and economical virtues of plants are indicated by their external appearances. Sir Isaac Newton hath attempted to show, that from the colours of bodies we may form a probable conjecture of the size of their constituent parts by which the rays of light are reflected.

No man can pretend to set limits to the discoveries that may be made by human genius and industry, of such connexions between the latent and the sensible qualities of bodies. A wide field here opens to our view, whose boundaries no man can ascertain, of improvements that may hereafter be made in the information conveyed to us by our senses.

CHAPTER XXII.

OF THE FALLACY OF THE SENSES.

COMPLAINTS of the fallacy of the senses have been very common in ancient and in modern times, especially among the philosophers and if we should take for granted all that they have said on this subject, the natural conclusion from it might seem to be, that the senses are given to us by some malignant demon on purpose to delude us, rather than that they are formed by the wise and beneficent Author of Nature, to give us true information of things necessary to our preservation and happiness.

The whole sect of Atomists among the ancients, led by Democritus, and afterwards by Epicurus, maintained, that all the qualities of bodies which the moderns call secondary qualities, to wit, smell, taste, sound, colour, heat, and cold, are mere illusions of sense, and have no real existence. Plato maintained, that we can attain no real knowledge of material things; and that eternal and immutable ideas are the only objects of real knowledge. The Academics and Sceptics anxiously sought for arguments to prove the fallaciousness of our senses, in order to support their favourite doctrine, that even in things that seem most evident, we ought to withhold

assent.

Among the Peripatetics we find frequent complaints that the senses often deceive us, and that their testimony is to be suspected, when it is not confirmed by reason, by which the errors of sense may be corrected. This complaint they supported by many common-place instances; such as, the crooked appearance of an oar in water; objects being magnified, and their distance mistaken in a fog; the sun and moon appearing about a foot or two in diameter, while they are really thousands of miles; a square tower being taken at a distance to be round. These, and many similar appearances, they thought to be sufficiently accounted for from the fallacy of the senses and thus the fallacy of the senses was used as decent cover to conceal their ignorance of the real causes of such phenomena, and served the same purpose as their occult qualities and substantial forms.

Des Cartes and his followers joined in the same complaint Antony le Grand, a philosopher of that sect, in the first chapter of his Logic, expresses the sentiments of the sect as follows: "Since all our senses are fallacious, and we are frequently deceived by them, common reason advises, that we should not put too much trust in them, nay, that we should suspect falsehood in every thing they represent; for it is imprudence and temerity to trust to those who have but once deceived us; and if they err at any time, they may be believed always to err. They are given by nature for this purpose only, to warn us of what is useful and what is hurtful to us. The order of nature is perverted when we put them to any other use, and apply them for the knowledge of truth."

When we consider, that the active part of mankind, in all ages from the beginning of the world, have rested their most important concerns upon the testimony of sense, it will be very difficult to reconcile their conduct with the speculative opinion so generally entertained of the fallaciousness of the senses. And it seems to be a very unfavourable account of the workmanship of the Supreme Being, to think that he has given us one faculty to deceive us, to wit, our senses, and another faculty, to wit, our reason, to detect the fallacy.

It deserves, therefore, to be considered, whether the fallaciousness of our