of a given length as a measure of comparative duration at two distant points on the globe's surface. And when he had done this, he might have been disposed to declare, on the authority of his senses and personal observation, that two portions of time, measured in different latitudes, were the same, although they were in fact different.

But here comes the question: Are his senses to blame for this mistake? Not at all. The testimony of the senses and of observation, as far as it went, was correct. The mistake is evidently to be attributed to erroneous deduction. The conclusion was bottomed on the great and undoubted principle of reasoning, that the laws of nature are uniform. But then there were various assumptions in this particular case, viz., that the earth is circular and not a spheroid; that the same quantity of the attractive force of the earth operates on the pendulum at every point in the earth's surface, &c. Here is the foundation of the mistake; in certain facts precipitately assumed as grounds of reasoning, and in the deductions from them, and not in the senses.

◊ 91. Of mistakes in judging of the motion of objects.

"Many false judgments," it is further remarked by Dr. Reid," that are accounted deceptions of sense, arise from our mistaking relative motion for real or absolute motion. These can be no deceptions of sense, because by our senses we perceive only the relative motions of bodies; and it is by reasoning that we infer the real from the relative which we perceive. A little reflection may satisfy us of this.

"It was before observed, that we perceive extension to be one sensible quality of bodies, and thence are necessarily led to conceive space, though space be of itself no object of sense. When a body is removed out of its place, the space which it filled remains empty till it is filled by some other body, and would remain if it should never be filled. Before any body existed, the space which bodies now occupy was empty space, capable of receiving bodies, for no body can exist where there is no space to contain it. There is space, therefore, wherever bodies exist or can exist.

"Hence it is evident that space can have no limits. It is no less evident that it is immoveable. Bodies placed in it are moveable, but the place where they were cannot be moved; and we can as easily conceive a thing to be moved from itself, as one part of space brought nearer to, or removed further from another.

"This space, therefore, which is unlimited and immoveable, is called by philosophers absolute space. Absolute or real motion is a change of place in absolute space.

"Our senses do not testify the absolute motion or absolute rest of any body. When one body removes from another, this may be discerned by the senses; but whether any body keeps the same part of absolute space, we do not perceive by our senses. When one body seems to remove from another, we can infer with certainty that there is absolute motion; but whether in the one or the other, or partly in both, is not discerned by sense.

"Of all the prejudices which philosophy contradicts, I believe there is none so general as that the earth keeps its place unmoved. This opinion seems to be universal, till it is corrected by instruction, or by philosophical speculation. Those who have any tincture of education are not now in danger of being held by it, but they find at first a reluctance to believe that there are antipodes; that the earth is spherical, and turns round its axis every day, and round the sun every year. They can recollect the time when reason struggled with prejudice upon these points, and prevailed at length, but not without some effort.

"The cause of a prejudice so very general is not unworthy of investigation. But that is not our present business. It is sufficient to observe, that it cannot justly be called a fallacy of sense; because our senses testify only the change of a situation of one body in relation to other bodies, and not its change of situation in absolute space. It is only the relative motion of bodies that we perceive, and that we perceive truly. It is the province of reason and philosophy, from the relative motions which we perceive, to collect the real and absolute motions which pro

duce them.

"All motion must be estimated from some point or place

which is supposed to be at rest. We perceive not the points of absolute space, from which real and absolute motion must be reckoned; and there are obvious reasons that lead mankind, in a state of ignorance, to make the earth the fixed place from which they may estimate the various motions they perceive. The custom of doing this from infancy, and of using constantly a language which supposes the earth to be at rest, may perhaps be the cause of the general prejudice in favour of this opinion.

"Thus it appears, that if we distinguish accurately between what our senses really and naturally testify, and the conclusions which we draw from their testimony by reasoning, we shall find many of the errors, called fallacies of the senses, to be no fallacy of the senses, but rash judgments, which are not to be imputed to our senses."

§ 92. Of mistakes as to the distances and magnitude of objects. One class of the fallacies by means of the senses is made up of those errors we commit in our perceptions of the distance of objects. Our sight, it is said, often represents objects to be near which are distant, and objects to be distant which are near. That we often form erroneous judgments as to the distance of objects, is true; but it is a mistaken sentiment which ascribes these erroneous opinions to the misrepresentations of the sight in itself considered.

Take the case of the sun and moon. Those heavenly bodies, as they come under the cognizance of sight, appear very small, but, in point of fact, are known to be very large. Still, in this very instance (although this is one of the cases most frequently referred to by the expositors of the alleged weaknesses and errors of the senses), it cannot be shown that there is any deception practised upon us by that sense. It has sufficiently appeared that extension, figure, the magnitude and the distance of bodies, are not direct objects of sight, and that our notions of them are not original in that sense, but are acquired. While, therefore, we have a direct acquaintance with colours by means of sight, it happens that, in estimating the distance of objects by the same sense, we are obliged to call in the aid of the intimations of the touch, and to make use also

of comparison and judgment. And hence we are able to fix on this general principle, that the apparent magnitude of an object will vary with its distance. It is clear, therefore, that there is no deception practised upon us. When, by such calculations as we are able to make, we have ascertained the distance of the sun and moon, then every one is satisfied that their apparent magnitude or their appearance to the eye is just such as it should be; and that the eye gives to us precisely the same representation as in any other instance of visible objects presented to it. It gives such a view of the object as it was designed to give; and teaches us here the same as it teaches us constantly.

(II.) Another class of errors are those of magnitude. The notions which we form on that subject also are acquired, and not original. We judge objects to be great or small in comparison with ourselves or with one another, and not in consequence of anything which is directly or immediately perceived in the objects themselves. We might call many objects small which happened to be of the size of a particular diamond, and yet not inconsistently speak of the diamond itself as a very large one; and this for the simple reason that our notions of large and small are not absolute but relative, and are formed by repeated acts of comparison. If there were but one object in creation besides ourselves, and if we could not reason from ourselves to that object, we could not possibly form any notion of its magnitude as distinct from the mere idea of extension. It is very clear, our senses could not, of themselves, authorize us to speak of such an object as large or small. Nor could it be done by reasoning, inasmuch as there are supposed to be no other objects with which to compare it.—These few remarks and illustrations can hardly fail to evince, that such mistakes as may exist in regard to the distance and magnitude of objects, are not exclusively attributable to the senses.

93. The senses liable to be diseased.

There is one respect, however, in which it is perhaps true that we can speak with propriety of deceptions arising from the cause now under consideration. The body,

as a whole, being liable to be diseased, the senses, as a part of the physical system, are of course not exempted from this liability. As a mere question of fact, it cannot be deemed a matter of doubt that the senses are often physically disordered, and at such times all persons are liable to be led astray by them. What is sweet to persons ordinarily, may appear bitter to one with a diseased palate; what is white to the mass of mankind, may appear of a yellow hue to one whose organ of sight is diseased; the physical condition of the sense of touch may be so perverted as to lead the diseased person to imagine he is made of glass or feathers instead of flesh and blood. But it is surely enough to say, in respect to cases of this kind, that such is the condition of humanity, the sad but common allotment of mankind. What principle in our mental constitution is not liable to be perverted? What susceptibility is not liable to find its action suspended? In our general conduct, we rely, and very correctly, on the MEMORY; but the laws of memory may be disorganized by what may be termed a mental disease. We rely with equal readiness on the REASONING power; no one doubts that its conclusions are a ground of belief. But of what value is reasoning when uttered in the ravings of a madman, or when drawing its conclusions in a lunatic asylum ?—It follows, therefore, if the senses deceive us in the case we are now attending to, the fault, if such it is to be considered, is not an exclusive one. It belongs to other parts of our nature also, not excepting its noblest and most trustworthy powers. And if we must reject the testimony of the senses simply because they are liable to be diseased, we must, for the same reason and in consistency with ourselves, reject the testimony of memory, of reason, and even of consciousness.

94. On the real existence of a material world.

It will be noticed that, in what has been said, we have taken for granted the actual existence of an external, material world. Certain it is, that no man who has the ordinary constitution of a man can doubt the reality of such an external, material creation. All external nature is operating upon us from the very moment of our birth; and