neal motion will continually exist in every part of the revolving portion, and in every point of the curve which it describes during its revolution. And this rectilineal tendency will be a tendency to recede from the centre in every point of the revolving orbit, and to proceed in a tangent to the orbit at each point. These two tendencies, if not originally equal, must necessarily in all cases arrive at an equality. For the tendency towards the centre, called the centripetal tendency, that is, the law of union, operating first, if we suppose the motion approaches the centre, the tendency to recede from it, called the centrifugal tendency, will have its proportion to the centripetal continually increased as the orbit of revolution grows less, so as ultimately to equal the centripetal tendency, and restrain the motion from its central course, at which point it will no longer seek the centre, but revolve round it."

As our author holds that every atom of matter is formed by the motion of parts of the active substance, and every body formed by the motion of atoms; so he maintains, not only that the sun, moon, earth, planets, and stars, are penetrated by the same substance, but that each is the centre of a vortex of that substance, and that of these vortices some are included within others. "The subtle revolving fluid, the centre of whose vortex the earth occupies, not only surrounds, but pervades the earth, and other vortices their earths, to their centres; and the earth and planets are by its revolutions carried around on their own axes. The earth is an active mass, and all its component masses are severally as well as collectively inactive; but the earth and all its parts have various collective and separate movements, imparted from the fluid which surrounds, pervades, and constitutes it. Being immersed together with its proper surrounding sphere or vortex in the larger sphere or vortex of the sun, it is carried thereby in a larger orbit about the sun, at the same time that by the revolution of its proper sphere it rotates on its own axis."

Such is the most complete view which our limits will permit us to give of Mr Young's theory of motion. To the philosopher who considers experiment as the only test of truth, and who in all his inquiries employs his hands more than his head, we are fully aware that it will appear in no better light than as "the baseless fabric of a vision." Even to the intellectual philosopher who is not frightened at the word metaphysics, we are afraid that such an active substance as the author contends for, will appear as inadequate to the production of the phenomena of gravitation and repulsion as the material ether of Mr Jones and his followers. A being void of intelligence, whether it be material or immaterial, quiescent or motive, cannot be the subject of law, in the proper sense of the word. The laws of which Mr Young speaks as necessary to regulate the motions of the active substance, must be mere forces, applied by some extrinsic and superior power. And since motion, as it is essential to the active substance, is power without direction, agency without order, activity to no end; since it is of such a nature, that from its unguided agitations there could result neither connection, order, nor harmony; it follows that those extrinsic forces must be perpetually applied, because what is essential to any substance can never be destroyed or changed as long as the substance itself remains.

Forces producing order out of confusion can be applied only by a being possessed of intelligence; and if the immediate and perpetual agency of an intelligent being be necessary to regulate the motions of the active substance, that substance itself may be thought superfluous, and its very existence may be denied. Entia non sunt multiplicanda ab acie necessitate, is a rule of philosophizing which every man of science acknowledges to be just. And it will hardly be denied that the immediate and perpetual agency of an intelligent being upon Mr Jones's ethereal fluid, or even upon the matter of solid bodies themselves, would be capable of producing every kind of motion, without the instrumentality of a substance which is neither mind nor matter.

Such, we conceive, are the objections which our meta-physical readers may make to this theory. Part of their force, however, will perhaps be removed by the ingenious manner in which our author analyzes matter into an immaterial principle. But so much of it remains that the writer of this article is inclined to believe that no mechanical account can be given of the motions of the heavenly bodies, the growth of plants, and various other phenomena which are usually solved by attraction and repulsion. In the present age, philosophers in general are strangely averse to admitting on any occasion the agency of mind; yet as every effect must have a cause, it is surely not irrational to attribute such effects as mechanism cannot produce to the operation either of intelligence or instinct. To suppose the Deity the immediate agent in the great motions of the universe, has been deemed impious; and it must be confessed that very impious conclusions have been deduced from that principle. But there is surely no impiety in supposing, with the excellent Bishop of Cloyne, that the fluid which is known to pervade the solar system, and to operate with resistless force, may be animated by a powerful mind, which acts instinctively for ends of which itself knows nothing. For the existence of such a mind, no other evidence, indeed, can be brought than what is afforded by a very ancient and very general tradition, and by the impossibility of accounting for the phenomena upon principles of mere mechanism. Perhaps some of our more pious readers may be inclined to think that the Supreme Being has committed the immediate government of the various planetary systems to powerful intelligences, or angels, who, as his ministers, direct their motions with wisdom and foresight. Such an opinion is certainly not absurd in itself; and it seems to be countenanced by an ancient writer, who, though not known by the name of a philosopher, knew as much of the matter as any founder of the most celebrated school.

To object to either of these hypotheses, as has sometimes been done, that it represents the government of the world as a perpetual miracle, betrays the grossest ignorance; for we might as well call the movements of the bodies of men and brutes, which are certainly produced by minds, miraculous. We do not affirm that either hypothesis is certainly true; but they are both as probable and as satisfactory as the hypothesis which attributes agency to attraction and repulsion, to a subtle ether, or to a substance which is neither mind nor matter. Were the immediate agency of intellect to be admitted, there would be no room for many of those disputes which have been agitated amongst philosophers, about the increase or diminution of motion in the universe; because an intelligent agent, which could begin motion as well as carry it on, might increase or diminish it as he should judge proper. If instinctive agency, or something similar to it, be adopted, there is the same room for investigation as upon the principles of mechanism; because instinct works blindly, according to steady laws imposed by a superior mind, which may be discovered by observation of their effects. As we consider this as by far the more probable hypothesis of the two, we find ourselves involved in the following question: If a certain quantity of motion was originally communicated to the matter of the universe, how comes it to pass that the original quantity still remains? Considering the many opposite and contradictory motions which since the creation have taken place in the universe, and which have undoubtedly destroyed a great part of the original quantity, by what means has that quantity been restored? If this question can be resolved by natural means, it must be upon the principles of Newton; for, in every case where quantities and relations of quantities are required, it is the province of mathematics to supply the information sought; and all philosophers agree that Sir Isaac's doctrine of the composition and resolution of motion, though in what respects the heavenly bodies it may have no physical reality, is so mathematically just, as to be the only principle from which the quantity of motion, or the force of powers, can in any case be computed. If we choose to answer the question, by saying that the motion left is restored by the interposition of the Deity, then we might as well have had recourse to him at first, and say that he alone is the true principle of motion throughout the universe.

Before we are reduced to this dilemma, however, it is necessary, in the first place, to inquire whether there is or can be any real diminution of the quantity of motion throughout the universe? In this question the Cartesians take the negative side, and maintain that the Creator at the beginning impressed a certain quantity of motion on bodies, and that under such laws that no part of it could be lost, but the same portion of motion would be constantly preserved in matter; and hence they conclude, that if any moving body should strike on any other body, the former would lose no more of its motion than it communicated to the latter. Sir Isaac Newton takes the contrary side, and argues in the following manner: From the various compositions of two motions, it is manifest there is not always the same quantity of motion in the world; for if two balls, joined together by a slender wire, revolve with a uniform motion about their common centre of gravity, and at the same time that centre be carried uniformly in a right line drawn in the plane of their circular motion, the sum of the motions of the two balls, as often as they are in a right line, drawn from their common centre of gravity, will be greater than the sum of their motions when they are in a line perpendicular to that other. Hence it appears, that motion may be both generated and lost. But by reason of the tenacity of fluid bodies, and the friction of their parts, with the weakness of the elastic power in solid bodies, nature seems to incline much rather to the destruction than the production of motion; and, in reality, motion becomes continually less and less. For bodies which are either so perfectly hard or so soft as to have no elastic power, will not rebound from each other; and their impenetrability will only stop their motion. And if two such bodies equal to one another be carried with equal but opposite motions, so as to meet in a void space, by the laws of motion they must stop in the very place of concourse, lose all their motion, and be at rest for ever, unless they have an elastic power to give them a new motion. If they have elasticity enough to make them rebound with one fourth, one half, or three fourths, of the force they meet with, they will lose three fourths, one half, or one fourth, of their motion. And this is confirmed by experiments; for if two equal pendulums be let fall from equal heights, so as to strike full upon each other; if those pendulums be of lead or soft clay, they will lose all, or almost all, their motion; and if they be of any elastic matter, they will only retain so much motion as they receive from their elastic power.

Motion, therefore, being thus, in the opinion of this celebrated author, lost or absolutely destroyed, it is necessary to find some cause by which it may be renewed. Such renovation Sir Isaac attributes to active principles; for instance, the cause of gravity, whereby the planets and comets preserve their motions in their orbits, and all bodies acquire a great degree of motion in falling; and the cause of fermentation, whereby the heart and blood of animals preserve a perpetual warmth and motion, the inner parts of the earth are kept perpetually warmed, many bodies burn and shine, and the sun himself burns and shines, and with his light warms and cheers all things.

Elasticity is another cause of the renovation of motion mentioned by Sir Isaac. "We find but little motion in the world," says he, "except what plainly flows either from these active principles, or from the command of the willer."

With regard to the destruction or positive loss of motion, however, we must observe, that notwithstanding the high authority of Sir Isaac Newton, it is altogether impossible that any such thing can happen. All moving bodies which come under the cognizance of our senses are merely passive, and acted upon by something which we call powers or fluids, and which are to us totally invisible. Motion, therefore, cannot be lost without a destruction or diminution of one of these powers, which we have no reason to think can ever happen. When two pendulums rush against each other, the motion is the mere effect of the action of gravity; and that action, which in this case is the power, continues to be the very same whether the pendulum moves or not. Could motion, therefore, be exhausted in this case, we must suppose, that by separating two pendulums to the same distance from each other, and then letting them come together, for a great number of times, they would at last meet with less force than before. But there is certainly not the least foundation for this supposition; and no rational person will take it into his head, that supposing the whole human race had employed themselves in nothing else from the creation to the present day but in separating pendulums and letting them stop each other's motion, they would now come together with less force than they did at first. Power, therefore, which is the cause of motion, is absolutely indestructible. Powers may indeed counteract one another, or they may be made to counteract themselves; but the moment that the obstacle is removed, they show themselves in their pristine vigour, without the least symptom of abatement or decay.

Whether, therefore, we reckon the ultimate source of motion to be spiritual or material, it is plain that it must be to our conceptions infinite; neither will the phenomena of nature allow us to give any other explanation than we have done; for no power whatever can lose more than its own quantity, and it seems absurd to think that the Deity would create the world in such a manner that it should ultimately become immovable, and then have recourse to unknown principles to remedy the supposed defect. On the principle we have just now laid down, however, the matter becomes exceedingly plain and obvious. The Creator at first formed two opposite powers, the action of which is varied according to the circumstances of the bodies upon which they act; and these circumstances are again varied by the action of the powers themselves in innumerable ways upon one another, and the approach of one body to another, or their receding to a greater distance. Where these powers happen to oppose each other directly, the body upon which they act is at rest; when they act obliquely, it moves in the diagonal; or if the force acting upon one side is by any means lessened, the body certainly must move towards that side, as is evident from the case of the atmosphere, the pressure of which, when removed from one side of a body, will make it move very violently towards that side, and if we could continually keep off the pressure in this manner, the motion would assuredly be perpetual. We must not imagine that motion is destroyed because it is counteracted; for it is impossible to destroy motion by any means but removing the cause; counteracting the effect is only a temporary obstacle, and must cease whenever the obstacle is removed. Nature, therefore, having in itself an infinite quantity of motion, produces greater or lesser motions, according to the various action of the moving powers upon different bo- dies or upon one another, without a possibility of the general stock being either augmented or diminished; unless one of the moving powers were withdrawn by the Creator, in which case the other would destroy the whole system in an instant. As to the nature of these great original powers, we must confess ourselves totally ignorant; nor do we perceive any data from which the nature of them can be investigated. The elements of light, air, &c., are the agents; but in what manner they act, or in what manner they received their action, can be known only to the Creator himself.

Perpetual Motion, in Mechanics, a motion which is supplied and renewed from itself, without the intervention of any external cause; or it is an uninterrupted communication of the same degree of motion from one part of matter to another, in a circle or other curve returning into itself, so that the same momentum still returns undiminished upon the first mover.

The celebrated problem of a perpetual motion consists in the inventing of a machine which shall have the principles of its motion within itself. M. de la Hire has demonstrated the impossibility of any such machine, and shown that it amounts to this, namely, to find a body which is both heavier and lighter at the same time, or to find a body which is heavier than itself.