(sometimes called Moxomotapa, but im- properly, as Moma is here a general name for kingdom), is dignified in the early narratives with the title of empire. Accounts disagree so much regarding the limits which ought to be assigned to Motapa, that it is impossible to derive from them a consistent result. It is uncertain whe- ther it ever deserved the name of empire; at all events, at the present day, it appears to be but a geographical di- vision, comprising several kingdoms independent of each other, and regarding which little or nothing is known.

MOTION is now generally considered as incapable of de- finition, being merely a simple idea or notion received by the senses. The ancients, however, thought differently. Some defined of them defined it to be a passage out of one state into another, which conveys no idea to him who is ignorant of the nature of motion. The Peripatetic definition has been mentioned elsewhere, and shown to be wholly unintelligible, as well as the celebrated division, by the same sect, of mo- tion into four classes belonging to the three categories, qua- lity, quantity, and where (see Metaphysics). The Cartesi- ans, too, amongst the moderns, pretend to define motion by calling it a passage or removal of one part of matter, out of the neighbourhood of those parts to which it is imme- diately contiguous, into the neighbourhood of others. Bo- rrelli defines motion to be the successive passage of a body from place to place. Others say that it is the application of a body to different parts of infinite and immoveable space; and Mr Young, in his Essay on the Powers of Nature, has given as a definition of motion, change of place.

We have elsewhere offered our opinion of every possible attempt to define motion; but as the author of the last- quoted definition has endeavoured to obviate such objec- tions as ours, candour requires that he be heard for him- self. "It is said," he observes, "by some, that change im- plies motion, and therefore cannot be a part of its defini- tion, being the very thing defined. To this I answer, We are speaking of the sensible idea of motion, as it appears Motion. to our sight; now changes do appear to our view, and to all our senses, which give us no idea of motion. Changes in heat or cold; in colour, flavour, smell, sound, hardness, softness, pain, pleasure; in these, and many other ideas, changes do not produce ideas like that produced by a ball rolling or a stone falling. We may perhaps ultimately trace them to motion, but to insensible motions; to motions which arise only in reflection, and constitute no part of the actual idea of change. We can therefore conceive of change without conceiving at the same time of motion. Change is a generic idea, including many species; motion, as a sensible idea, is a species of that genus. Change is therefore a necessary part of the definition of motion; it marks the genus of the thing defined. Motion is a change; but as there are many species of change, which of those species is motion? The answer is, it is a change of place. This marks the species, and distinguishes it from change of colour, of temperament, and figure."

This is the ablest defence of an attempt to define motion that we have ever seen; and at first view the definition itself appears to be perfect. Aristotle, the prince of definers, considers a definition as "a speech declaring what a thing is." Every thing essential to the thing defined, and nothing more, must be contained in the definition. Now the essence of a thing consists of these two parts: first, what is common to it with other things of the same kind; and secondly, what distinguishes it from other things of the same kind. The first is called the genus of the thing; the second, its specific difference. The definition, therefore, consists of these two parts.

In obedience to this rule, the definition under consideration seems to consist of the genus, signified by the word change, and of the specific difference, denoted by the words of place. But does the speech change of place really declare what motion is? We cannot admit that it does; as, in our apprehension, a change of place is the effect of motion, and not motion itself. Suppose a lover of dialectic undertaking to define the stroke by which he saw his neighbour wounded with a bludgeon; what should we think of his art were he to call it a contusion on the head? He might say that contusion is a general term, as contusions may be produced on the arms, on the legs, and on various parts of the body; and as there are many species of contusion, if he were asked which of those species was the stroke to be defined, he might answer, "a contusion on the head." Here would be apparently the genus and specific difference; the former denoted by contusion, and the latter by the words on the head. But would this be a definition of a stroke? No, surely. A contusion on the head may be the effect of a stroke, but it can no more be the stroke itself, than a blow can be a bludgeon, or a flesh wound the point of a sword. Equally evident it is, that a change of place cannot be motion; because every body must have been actually moved before we can discern, or even conceive, a change of its place.

The act of changing the place would perhaps come nearer to a definition of motion; but so far would it be from "a speech declaring what motion is," that we are confident a man who had never by any of his senses perceived a body in actual motion, would acquire no ideas whatever from the words "act of changing place." He might have experienced changes in heat, cold, smell, and sound; but he could not possibly combine the ideas of such changes with the signification of the word place, were he even capable of understanding that word, which to us appears to be more than doubtful. See Metaphysics.

The distinctions of motion into different kinds have been no less various, and no less insignificant, than the several definitions of it. The moderns who reject the Peripatetic division of motion into four classes, yet consider it themselves as either absolute or relative. Thus we are told, that absolute motion is the change of absolute place, and that its celerity must be measured by the quantity of absolute space which the moving body passes through in a given time. Relative motion, on the other hand, is a mutation of the relative or vulgar place of the moving body, and has its celerity estimated by the quantity of relative space passed through.

Now it is obvious, that this distinction conveys no ideas without a further explanation of the terms by which it is expressed; but that explanation is impossible to be given. Thus, before we can understand what absolute motion is, we must understand what is meant by absolute place. But absolute place is a contradiction; for all place is relative, and consists in the positions of different bodies with regard to one another. Were a globe in the regions of empty space to be put in motion by Almighty Power, and all the rest of the corporeal world to be soon afterwards annihilated, the motion would undoubtedly continue unchanged; and yet, according to this distinction, it would be at first relative, and afterwards absolute. That the beginning of such a motion would be perceptible, and the remainder of it imperceptible, is readily granted; but on this account to consider it as of two kinds, is as absurd as to suppose the motion of the minute hand of a clock to be affected by our looking at it.

Leaving these unintelligible distinctions, therefore, we now come to consider a question of a very abstruse nature, but much agitated amongst philosophers, namely, What is the original source of motion in the creation? Is it natural to matter, or are we to ascribe it to the immediate and continual agency of some immaterial being? The former has been strenuously argued by the Cartesians, and the latter by the Newtonians. The arguments of the former, founded upon the chimerical hypothesis of vortices and the original construction of matter, were evidently inconclusive; and the hypothesis of Sir Isaac Newton, who asserted that it was naturally incapable of motion, appeared more probable. To account for the quantity of motion in the universe, therefore, it became necessary to have recourse either to the Deity, or to some subordinate spiritual agent; and this became the more necessary, as the doctrine of an absolute vacuum in the celestial spaces, that is, throughout the incomparably greatest part of the creation, was one of the fundamental maxims of the system. As it was absolutely denied that matter existed in these spaces, and as it was plain that the celestial bodies affected one another at immense distances, the powers of attraction and repulsion were naturally called in as the sources of motion by their impulse upon inert and sluggish matter. And these being admitted, a speculation ensued concerning their nature. Spiritual, it was confessed, they were; but whether they were to be accounted the immediate action of the Divine Spirit himself, or that of some subordinate and inferior spirit, was a matter of no little dispute. Sir Isaac Newton, towards the latter part of his life, began to relax somewhat of the rigidity of his former doctrine, and allowed that a very subtile medium, which he called ether, might be the cause of attraction and repulsion, and thus of all the phenomena of nature. Since his time the multitude of discoveries in electricity, the similarity of that fluid to fire and light, with the vast influence it exerts on every part of the creation with which we are acquainted, have rendered it extremely probable that the ether mentioned by Sir Isaac is no other than the element of fire, "the most subtile and elastic of all bodies, which seems to pervade and expand itself throughout the whole uni-

1 See Dr Reid's account of Aristotle's logic, in Lord Kames' Sketches of Man. 2 Siris, No. 163, &c. verses. Electrical experiments show that this mighty agent is everywhere present, ready to break forth into action, if not restrained and governed with the greatest wisdom. Being always restless and in motion, it actuates and enlivens the whole visible mass; is equally fitted to produce and to destroy; distinguishes the various stages of nature, and keeps up the perpetual round of generations and corruptions, pregnant with forms which it constantly sends forth and re-absorbs. So quick in its motions, so subtle and penetrating in its nature, so extensive in its effects, it seemeth no other than the vegetative soul or vital spirit of the world.

"The animal spirit in man is the instrument both of sense and motion. To suppose sense in the corporeal world would be gross and unwarranted; but locomotive faculties are evident in all its parts. The Pythagoreans, Platonists, and Stoics, held the world to be an animal; though some of them have chosen to consider it as a vegetable. However, the phenomena do plainly show, that there is a spirit that moves, and a mind or providence that presides. This providence, Plutarch saith, was thought to be in regard to the world what the soul is in regard to man. The order and course of things, and the experiments we daily make, show that there is a mind which governs and actuates this mundane system as the proper and real agent and cause; and that the inferior instrumental cause is pure ether, fire, or the substance of light, which is applied and determined by an infinite mind in the macrocosm or universe, with unlimited power, and according to stated rules, as it is in the microcosm with limited power and skill by the human mind. We have no proof, either from experiment or reason, of any other agent or efficient cause than the mind or spirit. When, therefore, we speak of corporeal agents or corporeal causes, this is to be understood in a different, subordinate, and improper sense; and such an agent we know light or elementary fire to be."

That this elementary fire, absorbed and fixed in all bodies, may be the cause of the universal principle of gravity, is made sufficiently evident by numberless experiments. Homberg having calcined in the focus of a burning glass some regulus of antimony, found that it had gained one tenth in weight, though the regulus, during the whole time of the operation, sent up a thick smoke, and thereby lost a considerable part of its own substance. It is vain to allege that any heterogeneous matter floating in the air, or that the air itself, may have been hurled into the mass by the action of the fire, and that by this additional matter the weight was increased; for it is known experimentally, that if a quantity of metal be even hermetically secured within a vessel of glass to keep off the air and all foreign matter, and the vessel be placed for some time in a strong fire, it will exhibit the same effect. "I have seen the operation performed," says Mr Jones, "on two ounces of pewter filings, hermetically sealed up in a Florence flask, which in two hours gained fifty-five grains, that is, nearly a seventeenth. Had it remained longer in the fire, it might probably have gained something more; as, in one of Mr Boyle's experiments, steel filings were found to have gained a fourth.

Of accounting for these effects there are but two possible ways. 1. If the quantity of matter be the same, or, in the case of calcination, be somewhat less, after being exposed to the action of the fire, while the gravity of the whole is become greater; then does it follow that gravity is not according to the quantity of matter, and of course is not one of its properties. 2. If there be an increase of the mass, it can be imputed to nothing but the matter of light or fire entangled in its passage through the substance, and so fixed in its pores, or combined with its solid parts, as to gravitate together with it. Yet it is certain, from the phenomenon of light darting from the sun, that this elementary fire does not gravitate till it is fixed in metal, or some other solid substance. Here then we have a fluid which gravitates, if it gravitate at all, in some cases and not in others; so that which way soever the experiment be interpreted, we are forced to conclude that elementary or solar fire may be the cause of the law of gravitation."

That it is likewise in many cases the cause of repulsion, is known to every one who has seen it fuse metals, and convert water and mercury into elastic vapour. But there is a fact recorded by Mr Jones, which seems to evince that the same fluid, which, as it issues from the sun, exhibits itself in the form of light and heat, is in other circumstances converted into a very fine air, or cold ether, which rushes very forcibly towards the body of that luminary. "As a sequel to what has been observed," says he, "concerning the impregnation of solid substances with the particles of fire, give me leave to subjoin an experiment of M. de Stair. He tells us, that upon heating red lead in a glass whence the air was exhausted, by the rays of the sun collected in a burning glass, the vessel in which the said red lead was contained burst in pieces with a great noise. Now, as all explosions in general must be ascribed either to an admission of the air into a rarefied space, or to what is called the generation of it, and as air was not admitted upon this occasion, it must have been generated from the calx within the vessel; and certainly was so, because Dr Hales has made it appear that this substance, like crude tartar, and many others, will yield a considerable quantity of air in distillation. What went into the metal therefore as fire, came out of it again as air; which in a manner forces upon us conclusions of inestimable value in natural philosophy, and such as may carry us very far into the most sublime part of it."

One of the conclusions which the ingenious author thinks thus forced upon us is, that the motions of the planets round the sun, as well as round their own axes, are to be attributed to the continual agency of this fluid, under its two forms of elementary fire and pure air. As fire and light, we know that it rushes with inconceivable rapidity from the body of the sun, and penetrates every corporeal substance, exerting itself sometimes with such force as nothing with which we are acquainted is able to resist. If it be indeed a fact, that this elementary fire, or principle of light and heat, afterwards cools, and becomes pure air, there cannot be a doubt but that under such a form it will return with great force, though surely in a somewhat different direction, towards the sun, forming a vortex, in which the planets are included, and by which they must of course be carried round the centre. Mr Jones does not suppose that the air into which the principle of light and heat is converted, is of so gross a nature as our atmosphere. He rather considers it as cool ether, just as he represents light to be ether heated; but he maintains that this ether, in its aerial form, though not fit for human respiration, is a better medium of fire than the air which we breathe.

This theory seems exceedingly plausible; and the author supports it by many experiments. He has not, indeed, convinced us that the solar light is converted or convertible into pure air; but he has, by just reasoning from undoubted facts, proved that the whole expanse of heaven, as far as comets wander, is filled not only with light, which is indeed obvious to the senses, but also with a fluid, which, whatever it may be called, supplies the place of the air in feeding the fire of these ignited bodies.

That the motion of the heavenly bodies should result from the perpetual agency of such a medium, appears to us Motion. a much more rational hypothesis than that which makes them act upon each other at immense distances through empty space. But the hypothesis is by no means so complete a solution of the phenomena as some of its fond admirers pretend to think it. This fluid, whether called ether, heat, light, or air, is still material; and the question returns upon him who imagines that it is sufficient to account for gravitation, repulsion, magnetism, cohesion, and the like.

What moves the fluid itself, and makes the parts of which it is composed cohere together? However widely it may be extended, it is incapable of positive infinity, and therefore may be divided into parts separated from each other; so that it must be held together by a foreign force, as well as a ball of lead or a piece of wax. As matter is not essentially active, the motion of this ether, under both its forms, must likewise be considered as an effect, for which we do not think that any propelling power in the body of the sun can be admitted as a sufficient cause. For how comes the sun to possess that power, and what makes the fluid return to the sun? We have no notion of power in the proper sense of the word, but as intelligence and volition; and, like the pious and excellent author of the Essay on the First Principles of Natural Philosophy, we are certain that the sun was never supposed to be intelligent.

Bishop Berkeley, who admits of light or ether as the instrumental cause of all corporeal motion, gets rid of this difficulty by supposing, with the ancients, that this powerful agent is animated. "According to the Pythagoreans and Platonists," says his lordship, "there is a life infused throughout all things; the ἀγγεῖον, ἀγγεῖον ῥύσις, an intellectual and artificial fire, an inward principle, animal spirit, or natural life, producing and forming within, as art doth without; regulating, moderating, and reconciling the various motions, qualities, and parts of the mundane system. By virtue of this life, the great masses are held together in their ordinary courses, as well as the minutest particles governed in their natural motions, according to the several laws of attraction, gravity, electricity, magnetism, and the rest. It is this gives instincts, teaches the spider her web, and the bee her honey. This it is that directs the roots of plants to draw forth juices from the earth, and the leaves and the cortical vessels to separate and attract such particles of air and elementary fire as suit their respective natures."

This life or animal spirit seems to be the same thing which Cudworth calls plastic nature, and which has been considered elsewhere. (See Metaphysics.) We shall therefore dismiss it at present, with just admitting the truth of the bishop's position, "that if nature be supposed the life of the world, animated by one soul, compacted into one frame, and directed or governed in all its parts by one supreme and distinct intelligence, this system cannot be accused of atheism, though perhaps it may of mistake or impropriety."

A theory of motion somewhat similar to that of Berkeley, though in several respects different from it, was not very long ago stated with great clearness, and supported with much ingenuity, in an Essay on the Powers and Mechanism of Nature, intended to improve, and more firmly establish, the grand superstructure of the Newtonian system. Mr Young, the author of the essay, admits, with most other philosophers of the present age, that body is composed of atoms which are impenetrable to each other, and may be denominated solid. These atoms, however, he does not consider as primary and simple elements, incapable of resolution into principles; but thinks that they are formed by certain motions of the parts of a substance immaterial and essentially active.

As this notion is uncommon, and the offspring of a vigorous mind, we shall consider it more attentively hereafter. It is mentioned at present as a necessary introduction to the author's theory of motion, of which he attributes both the origin and the continuance to the agency of this elementary substance pervading the most solid atoms of the densest bodies. Of every body and every atom he holds the constituent principles to be essentially active; but those principles act in such a manner as to counterbalance each other, so that the atom or body considered as a whole is inert, unless in so far as it resists the compression or separation of its parts. No body or atom can of itself begin to move, or continue in motion for a single instant; but, being pervious to the active substance, and coalescing with it, that substance, when it enters any body, carries it along with it, till, meeting some other body in the way, either the whole of the active substance lodged in the former body passes into the obstacle, in which case the impelling body instantly ceases to move; or else part of that substance passes into the obstacle, and part remains in the impelling body; and in this case both bodies are moved with a velocity in proportion to the quantity of matter which each contains, combined with the quantity of active substance by which they are respectively penetrated.

In order to pave the way for his proof of the existence of one uniform active substance, he observes, that "change being an essentially constituent part of motion, and change implying action, it follows that all motion implies action, and depends on an active cause. Every motion," he continues, "has a beginning, a middle, and an end. The beginning is a change from rest to motion; the middle is a continuance in motion; the end is a change from motion to rest." He then proceeds to show, that the beginning of motion is by an action begun; the continuance of motion by an action continued; and the end of motion by a cessation of action.

"The first of these positions is admitted by every body. That the continuance of motion is by an action continued, will be proved, if it shall be shown that the continuance of a motion is nothing different from its beginning, in regard to any point of time assumed in the continued motion. Now the beginning of motion," he says, "consists in the beginning of change of place. But if any given portions of time and of space are assumed, a body beginning to move in the commencement of that time, and in the first portion of the space assumed, then and there begins that particular motion: And whether before the body began to move in that space it was moving in other spaces and times, has no relation to the motion in question; for this being in a space and time altogether distinct, is a distinct motion from any which might have preceded it immediately, as much as from a motion which preceded it a thousand years before. It is therefore a new motion begun; and so it may be said of every assumable point in the continued motion. The term continued serves only to connect any two distinct motions, the end of one with the beginning of the other, but does not destroy their distinctness."

He then proceeds to combat, which he does very successfully, the arguments by which the more rigid Newtonians endeavour to prove that a body in motion will continue to be moved by its own inertia, till stopped by some opposite force. Having done this, he establishes the contrary conclusion by the following syllogisms:

1. Whatever requires an active force to stop its motion, is disposed to move; 2. But every body in motion requires an active force to stop its motion;

Siris, No. 277. Therefore every body in motion is disposed to move.

"II. Whatever is disposed to motion is possessed of action; But a body in motion is disposed to continue in motion; Therefore a body in motion is possessed of action.

Thus it appears that the middle part of any motion is action equally with the beginning.

"The last part of motion is its termination. It is admitted that all motion is terminated by an action contrary to the direction of the motion. It is admitted, too, that the moving body acts at the time its motion is destroyed. Thus the beginning and the end of any uniform motion are confessed to be actions; but all the intermediate continuation which connects the beginning with the end is denied to be action. What can be more unaccountable than this denial? Is it not more consonant to reason and analogy, to ascribe to the whole continued motion one uninterrupted action? Such a conclusion true philosophy, we think, requires us to make.

"To move or act, is an attribute which cannot be conceived to exist without a substance. The action of a body in motion is indeed the attribute of the body, and the body relatively to its own motion is truly a substance, having the attribute or quality of motion. But the body being a name signifying a combination of certain ideas, which ideas are found to arise from action, that action which is productive of those ideas the combination of which we denominate body, is of the nature of an attribute as long as it is considered as constituted of action. To this attribute we must necessarily assign its substance. The actions which constitute body must be actions of something, or there must be something which acts. Whence, then, is this active something, from whose agency we get the idea of body, or whose actions constitute body? Is it not sufficient that it is something active? A name might be surely given it, but a name would not render the idea more clear. Its description may be found in every sensation; it is colour to the eye, flavour to the palate, odour to the nose, sound to the ear, and feeling to the touch; for all our sensations are but so many ways in which this active something is manifested to us. A substratum of solidity philosophers have imagined to exist, and have in vain sought to find. Our active substance is the substratum so long sought for, and with so little success. We give it a quality by which it may be perceived; it acts. One modification of action produces matter; another generates motion. These modifications of action are modes of the active substance, whose presence is action. Matter and motion constitute the whole of nature. There is therefore throughout nature an active substance, the constituent essence of matter, and immediate natural agent in all effects."

By an argument which we do not think very conclusive, our author determines this active substance to be unintelligent. "In our sensations individually, not discovering," says he, "the traces, not seeing the characters of intelligence, but finding only action present and necessary, our inferences go no farther than our observations warrant us to do; and we conclude in all these things an action only, and that action unintelligent." Having given our opinion of real agency elsewhere (see Metaphysics), we shall not here stop to examine this reasoning. We may, however, ask, whether all our sensations individually be not excited for a certain end. If they be, according to our author's mode of arguing in another place, then the exciting agent should be an intelligent being. By this we are far from meaning to deny the reality of a secondary or instrumental cause of sensation which is destitute of intelligence. We are strongly inclined to think that there is such a cause, though our persuasion results not from this argument of our author's. In our opinion, he reasons better when he says, "that a subordinate agent constructed as the matter of creation, invested with perpetual laws, and producing Motion agreeably to those laws all the forms of being, through the varieties of which inferior intelligences can, by progressive steps, arrive ultimately at the Supreme Contriver, is more agreeable to our ideas of dignity, and tends to impress us with more exalted sentiments, than viewing the Deity directly in all the individual impressions we receive, divided in the infinity of particular events, and unlawful, by his continual presence in operations to our view insignificant and mean."

This active substance, or secondary cause, our author concludes to be neither matter nor mind. "Matter," says he, "is a being, as a whole quiescent and inactive, but constituted of active parts, which resist separation, or cohere, giving what is usually denominated solidity to the mass. Mind is a substance which thinks. A being which should answer to neither of these definitions, would be neither matter nor mind, but an immaterial, and, if I may say, an immental substance." Such is the active substance of Mr Young, which, considered as the cause of motion, seems not to differ greatly from the plastic nature, hyalarchical principle, or vis gematrix, of others. The manner in which it operates is indeed much more minutely detailed by our author than by any other philosopher, ancient or modern, with whose writings we have any acquaintance.

"Every thing," he says, "must be in its own nature either disposed to rest or motion; consequently the active substance must be considered as a being naturally either quiescent or motive. But it cannot be naturally quiescent, for then it could not be active, because activity, which is a tendency to motion, cannot originate in a tendency to rest. Therefore the active substance is by nature motive, that is, tending to motion. The active substance is not solid, and does not resist penetration. It is, therefore, incapable of impelling or of sustaining impulse. Whence it follows, that as it tends to move, and is incapable of having its motion impeded by impulse, it must actually and continually move; in other words, motion is essential to the active substance.

"In order that this substance may act, some other thing upon which it may produce a change is necessary; for whatever suffers an action, receives some change. The active substance, in acting on some other thing, must impart and unite itself thereto; for its action is communicating its activity. But it cannot communicate its activity without imparting its substance; because it is the substance alone which possesses activity, and the quality cannot be separated from the substance. Therefore the active substance acts by uniting itself with the substance on which it acts. The union of this substance with bodies is not to be conceived of as a junction of small parts intimately blended together and attached at their surfaces; but as an entire diffusion and incorporation of one substance with another in perfect coalescence. As bodies are not naturally active, whenever they become so, as they always do in motion, it must be by the accession of some part of the active substance. The active substance being imparted to a body, penetrates the most solid or resisting parts, and does not reside in the pores without, and at the surfaces of the solid parts. For the activity is imparted to the body itself, and not to its pores, which are no parts of the body; therefore, if the active substance remained within the pores, the cause would not be present with its effect, but the cause would be in one place and the effect in another, which is impossible.

"Bodies, by their impulse on others, lose their activity in proportion to the impulse. This is matter of observation. Bodies which suffer impulse acquire activity in proportion to the impulse. This also is matter of observation. In impulse, therefore, the active substance passes out of the impelling body into the body impelled. For since bo- Motion in motion are active, and activity consists in the presence of the active substance, and by impulse bodies lose their activity, therefore they lose their active substance, and the loss is proportional to the impulse. Bodies impelled acquire activity; therefore acquire active substance, and the acquisition is proportioned to the impulse. But the active substance lost by the impelling body ought to be concluded to be that found in the other; because there is no other receptacle than the impelled body to which the substance parted from can be traced, nor any other source than the active body whence that which is found can be derived. Therefore, in impulse, the active substance ought to be concluded to pass from the impelling body to the body impelled. The flowing of such a substance is a sufficient cause of the communication of activity, and no other rational cause can be assigned.

"The continued motion of a body depends not upon its inertia, but upon the continuance of the active substance within the body. The motion of a body is produced by the motion of the active substance in union with the body. It being evident, that since the active substance itself does always move, whatever it is united to will be moved along with it, if no obstacle prevent. In mere motion, the body moved is the patient, and the active substance the agent. In impulse, the body in motion may be considered as an agent, as it is made active by its active substance. While the active substance is flowing out of the active body into the obstacle or impelled body, the active body will press or impel the obstacle. For while the active substance is yet within the body, although flowing through it, it does not cease to impart to the body its own nature, nor can the body cease to be active because not yet deprived of the active substance. Therefore, during its passing out of the body, such portion of the active substance as is yet within, is urging and disposing the body to move, in like manner as if the active substance were continuing in the body; and the body being thus urged to move, but impeded from moving, presses or impels the obstacle.

"We see here," says our author, "an obvious explanation of impulse; it consists in the flowing of the motive substance from a source into a receptacle; and he thinks, that although the existence of such a substance had not been established on any previous grounds, the communication of motion by impulse does alone afford a sufficient proof of its reality.

He employs the agency of the same substance to account for many other apparent activities in bodies, such as those of fire, electricity, attraction, repulsion, elasticity, &c. All the apparent origins of corporeal activity serve, he says, to impart the active substance to bodies; and where activity is without any manifest origin, the active substance is derived from an invisible source."

Our limits will not permit us to attend him in his solution of all the apparent activities in bodies; but the orbicular motions of the planets have been accounted for in so many different ways by philosophers ancient and modern, and each account has been so little satisfactory to him who can think, and wishes to trace effects from adequate causes, that we consider it as our duty to furnish our readers with the account of this phenomenon which is given by Mr Young.

The question which has been so long agitated, "Whence is the origin of motion?" our author considers as implying an absurdity. "It supposes," says he, "that rest was the primitive state of matter, and that motion was produced by a subsequent act. But this supposition must ever be rejected, as it is giving precedence to the inferior, and inverting the order of nature." The substance which he holds to be the basis of matter is essentially active, and its action is motion. This motion, however, in the original element, was power without direction, agency without order, activity to no end. To this power it was necessary that a law should be superadded; that its agency should be guided to some regular purpose, and its motion conspire to the production of some uniform effects. Our author shows, or endeavours to show, by a process of reasoning which shall be examined elsewhere, that the primary atoms of matter are produced by the circular motion of the parts of this substance round a centre; and that a similar motion of a number of these atoms around another centre common to them all, produces what in common language is called a solid body; a cannon ball, for instance, the terrestrial globe, and the body of the sun, &c. In a word, he labours to prove, and with no small success, that a principle of union is implied in the revolving or circulating movements of the active substance.

"But we may also assume," he says, "a priori, that a principle of union is a general law of nature; because we see in fact all the component parts of the universe are united systems, which successively combine into larger unions, and ultimately form one whole." Let us then suppose the sun, with all his planets, primary and secondary, to be already formed for the purpose of making one system, and the orbits of all of them, as well as these great bodies themselves, to be pervaded by the active substance, which necessarily exists in a state of motion, and is the cause of the motion of every thing corporeal. "If to this motion a principle of union be added, the effect of such a principle would be a determination of all the parts of the active substance, and of course all the bodies to which it is united, towards a common centre, which would be at rest, and void of any tendency in any direction. But this determination of all the parts of the system towards a common centre tends to the destruction both of the motion of the active substance and of the system; for should all the parts continually approximate from a circumference towards a centre, the sun and planets would at last meet, and form one solid and quiescent mass. But to preserve existence, and consequently motion, is the first law of the active substance, as of all being; and it cannot be doubted, that to preserve distinct the several parts of the solar system, is the first law given to the substance actuating that system. The union of the system is a subsequent law.

"When the direct tendency of any inferior law is obviated by a higher law, the inferior law will operate indirectly in the manner the nearest to its direct tendency that the superior law will permit. If a body in motion be obliquely obstructed, it will move on in a direction oblique to its first motion. Now the law of union, which pervades the solar system, being continually obstructed by the law of self-preservation, the motion of the active substance, and of the bodies to which it is united, can be no other than a revolving motion about the common centre of approach, towards which all the parts have a determination. But when this revolution has actually taken place, it gives birth to a new tendency, which supersedes the operation of the law of self-preservation. It has been shown, that the motion essential to the active substance required to be governed by some law, to give being to an orderly state of things. Now, there are motions simple and motions complex; the more simple is in all things first in order, and out of the more simple the more complex arises in order posterior. The most simple motion is rectilinear; therefore a rectilinial motion is to be considered as that which is the original and natural state of things, and consequently to which all things tend. It will follow from hence, that when any portion of active substance in which the law of union operates, has in the manner above explained been compelled to assume a revolving motion, that is, a motion in some curve, a tendency to a rectilin-