Taken in its most enlarged sense, the word Physics comprehends the whole study of nature; and Natural Philosophy is a term of the same extent; but ordinary language, especially in Britain, employs both of these terms in a much narrower sense, which it is proper in this place to determine with some precision.

Under the article Philosophy, we gave a particular account of that view of nature in which the objects of our attention are considered as connected by causation; and we were at some pains to point out the manner in which this study may be successfully cultivated. By a judicious employment of the means pointed out in that article, we discover that the objects of our contemplation compose an universe, which consists, not of a number of independent existences solitary and detached from each other, but of a number of substances connected, by a variety of relations and dependencies, so as to form a whole, which may with great propriety be called the System of Nature.

This assembling of the individual objects which compose the universe into one system is by no means the work of a hasty and warm fancy, but is the result of sober contemplation. The natural historian attempts in vain to describe objects, by only informing us of their shape, colour, and other sensible qualities. He finds himself obliged, in describing a piece of marble, for instance, to tell us that it takes a fine polish; that it strikes fire with steel; that it burns to quicklime; that it dissolves in aquafortis, and is precipitated by alkalies; that with vitriolic acid it forms gypsum, &c.; and thus it appears, that even the description of any thing, with the view of ascertaining its specific nature, and with the sole purpose of discrimination, cannot be accomplished without taking notice of its various relations to other things. But what do we mean by the nature of any thing? We are ignorant of its essence, or what makes it that thing and no other thing. We must content ourselves with the discovery of its qualities or properties; and it is the assemblage of these which we call its nature. But this is very inaccurate. These do not constitute its essence, but are the consequences of it. Yet this is all we shall ever know of its nature. Now the term property is nothing but a name expressing some relation which the substance under consideration has to other things. This is true of all such terms. Gravity, elasticity, sensibility, gratitude, and the like, express nothing but certain matters of fact, which may be observed respecting the object of our contemplation in different circumstances of situation with regard to other things. Our distinct notions of individuals, therefore, imply their relations to other things.

The slightest observation of the universe shows an evident connection between all its parts in their various properties. All things on this earth are connected with each other by the laws of motion and of mind. We are connected with the whole of the solar system by gravitation. If we extend our observations to the fixed stars, the connection seems to fail; but even here it may be observed. Their inconceivable distance, it is true, renders it impossible for us to obtain any extensive information as to their nature. But these bodies are connected with the solar system by the sameness of the light which they emit with that emitted by our sun or any shining body. It moves with the same velocity; it consists, in most of them at least, of the same colours; and it is reflected, refracted, and reflected, according to the same laws.

In this unbounded scene of contemplation, our attention will be directed to the different classes of objects nearly in proportion to the interest we take in them. There is no thing in which we are so much interested as our fellow men; and one of the first steps that we make in our knowledge of nature, is an acquaintance with them. We learn their distinctive nature by attending to their characteristic appearances; that is, by observing their actions. We observe them continually producing, like ourselves, certain changes in the situation or condition of surrounding objects; and these changes are evidently directed to certain ends which respect themselves. Observing this subserviency of the effects which they produce to their own accommodation, we consider this adjustment of means to ends as the effect of an intention, since we experience it to be so in our own case, where we are conscious of this intention, and of these its effects. We therefore interpret those actions of other men, where we observe this adjustment of means to ends, as marks or signs of intention to them similar to our own; and thus a quality, or power, or faculty, is supposed in them by means of its sign, although the quality itself is not immediately cognisable by our senses. And as this intention in ourselves is accompanied by perception of external objects, knowledge of their properties, desire of good, aversion to evil, volition and exertion, without all of which we could not or would not perform the actions which we daily perform, we suppose the same perception, knowledge, desire, aversion, volition, and exertion in them. Thus, by the constitution of our mind, we consider the employment of means, by which ends terminating in the agent are gained, as the natural signs of design or intention. Art, therefore, or the employment of means, is the natural sign of intention; and wherever we observe this adjustment of means to ends, we infer the agency of design.

A small acquaintance with the objects around us, obliges us to extend this inference to a great number of beings besides our fellow men, namely, to the whole animal creation; for in all we observe the same subserviency to the ends of the agent in the changes which we find them continually producing in the objects around them. These changes are all adjusted to their own well-being. In every such case, therefore, we are forced, by the constitution of our own minds, to infer the existence of design or intention in these beings also. But in numberless changes produced by external objects on each other, we observe no such fitness in the effects; no such subserviency to the well-being of the agent. In such cases, therefore, we make no such inference of thought or design.

Thus, then, there is presented to our observation an important distinction, by which we arrange all external objects into two classes. The first resembles ourselves, in that giving external marks of that thought or intention of which we are conscious; and we suppose in them the other properties which we discover in ourselves, but cannot immediately observe in them, viz. thought, perception, memory, foresight, and all that collection of faculties which we feel in ourselves, and which constitute the animal. The other class of objects exhibits no such appearances; and we make no such inference. Hence we divide the whole of external nature into the classes of thinking and unthinking beings.

Our first judgments about these classes will be very inaccurate; and we will naturally ascribe the differences between which we do not very well understand, to the differences known in organic structure, which we very clearly observe. But when we have knocked down or perhaps smothered an animal, we find that it no longer gives the former marks of thought and intention; and that it now resembles the class of unthinking beings; and yet it still retains all that fit- ness of organical structure which it had before; it seems only to want the intention and the will. This obliges us to conclude that the distinction does not arise from a difference in organical structure, but from a distinct substance, common to all thinking beings, though separable from their organical frame. To this substance we ascribe thought, intention, contrivance, and all that collection of faculties which we feel in ourselves. To this substance in ourselves we refer all sensations, pleasures, pains, remembrances, desires, purposes; and to this aggregate, however imperfectly understood, we give the name mind. Our organical frame, which seems to be only the instrument of information and operation to the mind, we call our body.

As the animating principle is not, like our body, the immediate object of the senses, we naturally conceive it to be a substance essentially different from those which are the objects of our senses. The rudest people have shown a disposition to form this conclusion. Observing that animal life was connected with breathing, it was natural to imagine that breathing was living, and that breath was life. It is a remarkable fact, that in most languages the term for expressing breath is at least one of the terms for expressing the soul; in Sanskrit, spiritus, in the Hebrew, Greek, and Latin, express both; ghed or ghosts, in the Teutonic comes from ghedien, to breathe or sigh; ducha or ducha, the soul, in Slavonic, comes from duchat, to breathe; so, in the Gaelic, does anal come from anam; and the same relation is found between the two words in the Malay and other eastern languages. We believe that most persons can recollect some traces of this notion in their early conceptions of things; and many, who do not consider themselves as uncultivated, believe that the soul quits the body along with the last breath. Amongst the Tartar nations hanging is regarded with particular horror, on account of the ungrateful and filthy exit which the soul is obliged to make from the body. But the observation of the same appearances of thought and intention in fishes, and other animals which do not breathe, would soon show that this was but a rude conception. Very little refinement indeed is necessary to convince us that air or breath cannot be the substance which thinks, wishes, and designs; and that the properties of this substance, whatever it is, must be totally different from, and incompatible with, anything that we know of the immediate objects of our senses.

Hence we are led to conclude that there are two kinds of substances in nature; one which is the principle of sensation, and therefore cannot be the object of our senses, any more than light can be the object of the microscope. This substance alone can feel, think, desire, and propose, and is the object of reflection alone. The objects of our senses compose the other class, and therefore can have none of the other properties which are not cognizable by the senses. These have all the properties which our senses can discover; and we can have no evidence of their having any other, nor indeed any conception of their having them. This class is not confined to the unorganized masses of matter; for we see that the bodies of animals lose after death that organized form, and are assimilated to all the rest of unthinking beings. It has arisen from such views as this, that whilst all nations have agreed to call this class of objects by the name of body, which originally expresses our organical frame, some nations, farther advanced in cultivation or refinement, have contrived an abstract term to express this general substance of which all inanimate beings are composed. Such a term we have in the words materia and mater.

Matter, then, is that substance which is immediately cognizable by our senses. Whatever, therefore, is not thus immediately cognizable by our senses is not material, and is expressed by a negative term, and called immaterial; and hence it is that mind is said to be immaterial. It is of importance to keep in mind this distinction, though merely grammatical. Little more is necessary for detecting the sophisms of Helvetius, Mirabeau, and others, who have been anxious to remove the ties of moral and religious obligation, by lowering our conceptions of our intellectual nature. It will also serve to show how hastily they have formed their opinions, who have ascribed to the immediate agency of mind all those relations which are observed in the actions of bodies upon each other at a distance. The connecting principles of such relations e distante, if there be any such, are not the immediate objects of our senses; they are therefore immaterial. But it does not follow that they are minds. There may be many immaterial substances which are not minds. We know nothing of any object whatever, except by the observation of certain appearances, which suggest to our minds the existence and agency of its qualities or powers. Such phenomena are the natural signs of these qualities, and it is to such signs that we must always have recourse when we wish to conceive without ambiguity concerning them. What is the characteristic phenomenon of mind, or what is the distinguishing quality which brings it into view? If it is intention; and it may be asserted with the utmost confidence, that we have no other mark by which mind is immediately suggested to us, or which would ever have made us suppose that there existed another mind besides our own. The phenomenon by which this quality is suggested to us is art, or the employment of means to gain ends; and the mark of art is the supposed conduciveness of these ends to the well-being of the agent. Where this train is not observed, design or intention is never thought of; and therefore where intention is not perceived in any immaterial substance, if any such has ever been observed, it is an abuse of language to call it mind. We do not think that even perception and intelligence entitle us to give the name mind to the substance in which they are inherent, because it is from marks of intention alone that we infer the existence of mind; and although these must be accompanied with perception and intelligence, it does not follow that the substance which can perceive and understand must also desire and propose. However difficult we may find it to separate them, they are evidently separable in imagination. And let not this assertion be too hastily objected to; for the separation has been made by persons most eminent for their knowledge and discernment. When Leibnitz ascribed to his monades, or what we call the ultimate atoms of matter, a perception of their situation in the universe, and a motion precisely suited to this perception, he was the farthest in the world from supposing them animated or endowed with minds. It is true, indeed, that others, who think and call themselves philosophers, are much more liberal in their application of this term. A modern author of great metaphysical eminence says, "I call that mind which moves, and that body which is moved." This class of philosophers assert that no motion whatever is begun except by the agency of an animating principle, which, after Aristotle, they call Nature, and which has in these days been exalted to the rank of a god. All this jargon, for it is nothing else, has arisen from the puzzle in which naturalists think themselves involved in attempting to explain the production of motion in a body at a distance from that body which is conceived as the cause of this motion. After having been reluctantly obliged, by the reasonings of Newton, to abandon their methods of explaining such phenomena by the impulses of an intervening fluid, nothing seemed left but the assertion that these motions were produced by minds, as in the case of our own exertions. These explanations, if they deserve the name, cannot be objected to in any other way than as an abuse of language, and as the introduction of an unmeaning jargon. We have, and can have, no notion of mind different from those of our own minds; and we discover the existence of other minds, as we discover the existence of bodies, by means of phenomena which are characteristic of minds, that is, which resemble those phenomena that follow the exertion of our mental faculties, that is, by the employment of means to attain selfish ends; and where such appearances are not observed, no existence of a mind is inferred. When we see a man fall from the roof of a house, and dash out his brains on the pavement, we never ascribe this motion to his mind. Although the fitness of many of the celestial motions for most important purposes makes us suppose design and contrivance somewhere, and therefore a Supreme Mind, we no more think of inferring a mind in the earth from the fitness of its motions for purposes most beneficial to its inhabitants, than of inferring a mind in a bit of bread from its fitness for nourishing our bodies. It is not from the mere motions of animals that their minds are inferred, but from the conduciveness of these motions to the well-being of the animal.

The term mind, therefore, in the ordinary language of all men, is applied to what desires and wills at the same time that it perceives and understands. If we call that mind which produces motion, we must derive our notions of its qualities or attributes from observing their effects. We must therefore discover the general laws by which they act, that is, the general laws observed in those motions which we consider as their effects. Now these are the general laws of motion; and in none of these can we find the least coincidence with what we are accustomed to call the laws of mind. Nay, it has been the total want of similarity which has given rise to the distinction which all men, in all ages and countries, have made between mind and matter. This distinction is found in all languages; and it is an unpardonable liberty which men take with language when they use a term of distinction, a specific term, to express things of a different species. What these authors have been pleased to call mind, the whole world besides have called by another name, force; which, though borrowed from our own exertions, is yet sufficiently distinctive, and never leads us to confound things which are different, except in the language of some modern philosophers, who apply it to the laws of the agency of mind, and, when speaking of the force of motives, &c. commit the same mistakes which the followers of Aristotle commit in the use of the term mind. Force, in the language of these philosophers, means what connects the operations of mind; as mind, in the language of Lord Monboddo, is that which connects the operations of body.

Those persons are not less to blame who consider this Nature of Aristotle, this principle of motion, as an existence or substance different both from matter and from the minds of intelligent creatures. Aristotle calls it in some places ἀνάγκη. He might with equal propriety, and equal consistency with his other doctrines, have called mind ἀνάγκη τῆς ὕλης, or ἀνάγκη τῶν ὑποκειμένων. Besides, we have no evidence for the separability of this ἀνάγκη ὑποκειμένων from body, as we have for the separability of such minds as our own, the genuine ψυχή. Nay, his whole doctrines, when maturely considered, assume their absolute inseparability.

This doctrine of elemental minds, therefore, as the immediate causes of the phenomena of the material world, is an abuse of language. It is a jargon; and it is a frivolous abuse, for it offers no explanation whatever. The phenomena are totally unlike the phenomena of ordinary minds, and therefore receive no explanation from them; and since our knowledge of these ὑποκειμένων or quasi minds must be derived entirely from the phenomena, it will be precisely the same, although we express it in common language. We shall not indeed raise the wonder of our hearers, as those do who fill the world with minds which they never suspected to exist; but, on the other hand, we shall not bewilder their imaginations, confound their ideas, and mislead their judgments.

Some philosophers have attended only to the appearances of fitness which are exhibited in every quarter of the universe; and, by arranging these into different classes and interpreting them as indications of thought and instinctive actions, have acquired the knowledge of many classes of sentient and intelligent beings, actuated by propensities, and directed by reason. Whilst the contemplation of these appearances indicates thought and design in any individual of one of these classes, and brings its propensities and purposes of action, and the ends gained by these actions, into view, the contemplation of these propensities, purposes, and ends, occasions an inference of a much more general kind. All these intelligent beings give indications of knowledge and of power; but their knowledge bears, in general, no proportion to their power of producing changes in nature, and of attaining important ends; and their power is neither always, nor in the most important cases, the consequence of their knowledge. Where the effect of their actions is most eminently conducive to their most important interests, the power of attaining these valuable ends is generally independent of any attention to the fitness of the means, and the exertion is frequently made without even thinking of the important end. The well-being of the individual is secured against any danger from its ignorance, indolence, or inattention, by an instinctive propensity, which leads it to the performance of the necessary action, which is thus made immediately and ultimately desirable, without any regard to its ultimate and important end. Thus, in our own nature, the support of animal life, and the improvement of the means of subsistence by a knowledge of the objects which surround us, are not intrusted to our apprehensions of the importance of these ends, but are committed to the surer guides of hunger and curiosity.

The same observers discover a connection between the individuals of a class, different from that which arises from the mere resemblance of their external appearance, or even of their propensities and pursuits; the very circumstances which produced the classification. They observe, that these propensities are such, that whilst each individual seeks only its own enjoyment, these enjoyments are sensible in general such as contribute to the support of the species, and the enjoyment of other individuals. Thus, in the classes of animals, and in human nature, the continuance of the race, and the enjoyment of the whole, are not intrusted to the apprehension we entertain of the importance of these ends, but are produced by the operation of sexual love and the love of society.

The same observers find that even the different classes of sentient beings are connected together; and whilst the whole of each class aim only at their own enjoyment, they contribute, in some way or other, to the well-being of the other classes. Even man, the selfish lord of this subordinate world, is not the unconnected inhabitant of it. Having cannot, in every instance, reap all the fruits of his situation, without contributing to the enjoyment of thousands of the brute creation. Nay, it may be proved to the satisfaction of every intelligent man, that whilst one race of animals, in consequence of its peculiar propensities, subsists by the destruction of another, the sum total of animal life and enjoyment is prodigiously increased.1

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1 See a very judicious dissertation on this curious and puzzling subject, entitled a Philosophical Survey of the Animal Creation; where it appears that the increase of animal life and enjoyment which is produced by this means, beyond what could possibly obtain without it, is beyond all conception. See likewise the edition of King's Origin of Evil, by Dr Law. Thus the whole assemblage seems connected, and jointly employed in increasing the sum total of possible happiness. This fitness of the various propensities of sentient and intelligent beings, this subserviency to a general purpose, strikes these observers as a mark of intention, evidently distinct from, and independent of, all the particular intentions, and superior to them all; and thus it irresistibly leads them to infer the existence of a Supreme Mind, directing the whole of this intellectual system, whilst the individuals of which it consists appear the unconscious instruments in the hand of a great Artist, with which he executes his grand and beneficent purposes.

But the observation extends yet further. The bodies of the inanimate creation are not only connected with each other by a mutual dependence of properties, and the relation of causation, but they are also connected with the sentient beings by a subserviency to their purposes of enjoyment. The philosopher observes that this connection is admirably kept up by the constancy of natural operations and the expectations of intelligent beings. Had either of these circumstances been wanting, had either the operations of nature been without rule, or had sentient beings possessed no perception or expectation of their uniformity, the subserviency would be totally at an end. This adjustment, this fitness, of which the result is the enjoyment of the sentient inhabitants of the universe, appears to be the effect of an intention of which this enjoyment is the final cause. This constancy, therefore, in the operations of nature, both in the intellectual and material world, and the concomitant expectation of sentient beings, appear to be the effects of laws imposed on the different parts of the universe by the Supreme Mind, who has formed both these classes of beings so admirably suited to each other.

To such observers the world appears a work of art, a system of means employed for gaining certain proposed ends, and it carries the thoughts forward to an artist; and we infer a degree of skill, power, and good intention in this artist, proportioned to the ingenuity, extent, and happy effect which we are able to discern in his works. Such a contemplation of nature, therefore, terminates in natural theology, or the discovery of the existence and attributes of God.

Our notions of this Supreme Mind are formed from the indications of design which we observe, and which we interpret in the same way as in the actions of men. These notions therefore will differ from our notions of other minds only in the degrees which we are able to observe, and which we assign to these faculties; for the phenomenon or the effect is not only the mark, but also the measure of its supposed cause. These degrees must be ascertained by our own capacity of appreciating the extent, the multiplicity, and the variety of the contrivance. Accordingly, the attributes of the Supreme Mind, in the theological creed of a rude Indian, are much more limited than in that of a European philosopher. In proportion as our understandings are enlarged, and as our acquaintance with the operations of nature around us is extended, we shall perceive higher degrees of power, of skill, and of kind intention; and since we find that the scene of observation is unbounded, we cannot affix any boundaries to these attributes in our own imagination, and we are ready to suppose that they are infinite or unbounded in their own nature. When our attentive survey of this universe, and a careful comparison of all its parts, as far as we can understand or appreciate them, have made us conclude that it is one design, the work of one artist, we are under the necessity of inferring, that, with respect to this universe, his power, wisdom, and benevolence, are indeed infinite.

When men have been led to draw this conclusion from the appearances of fitness which are observed everywhere around them, they consider that constancy which they observe in natural operations, whether in the material or the intellectual system, and that expectation of confidence in this constancy, which renders the universe a source of enjoyment to its sentient inhabitants, as the consequences of laws imposed by the Almighty Artist on his works, in the same manner as they would consider the constancy in the conduct of any people as the consequences of laws promulgated and enforced by the supreme magistrate.

There can be no doubt of this view of nature being extremely captivating, and likely to engage the curiosity of moral sentiment and speculative men; and it is not surprising that the phenomena of mind have been keenly studied in all ages. This part of the study of nature, like all others, was first cultivated in subserviency to the wants of social life; and the general laws of moral sentiment were the first phenomena which were considered with attention. This gradually ripened into a regular system of moral duty, accompanied by its congenial study, the investigation or determination of the summum bonum, or the constituents of human felicity; and these two branches of intellectual science were always kept in a state of association by the philosophers of antiquity. Jurisprudence, the science of government, legislation, and police, were also first cultivated as arts, or at least in immediate subserviency to the demands of cultivated society; and all these so nearly related parts of the study of human nature had made a very considerable progress, in the form of maxims or precepts for directing the conduct, before speculative men, out of mere curiosity, treated them as subjects of philosophical study. Our moral sentiments, always involving a feeling of obligation, are expressed in a language considerably different from the usual language of pure philosophy, speaking of things which ought to be, rather than of things which are; and this distinction of language was increased by the very aim of the writers, which was generally to influence the conduct as well as the opinions of their scholars. It was reserved for modern times to bring this study into the pure form of philosophy, by a careful attention to the phenomena of moral sentiment, and classing these according to their generality, and ascertaining their respective ranks by an appeal to experiment, that is, to the general conduct of mankind; and thus it happens that in the modern treatises on ethics, jurisprudence, &c., there is less frequent reference made to the officia or duties, that is, the constituents of the summum bonum, than amongst the ancients, and a more accurate description of the human mind, and discrimination of its various moral feelings.

It was hardly possible to proceed far in these disquisitions without attending to the powers of the understanding and the origin of ideas. Differences of opinion were supported by reasonings, other intellectual attempts at reasoning. Both sides could not be in the right, and there must be some court of appeal. Rules of argumentation behoved to be acquiesced in by both parties; and it could hardly escape the notice of some curious minds, that there were rules of truth and falsehood, as well as of right and wrong. Thus the human understanding became an object of study, first in subserviency to the demands of the moralist, but afterwards for its own sake; and it gradually grew up into the science of logic. Still further refinement produced the science of metaphysics, or the philosophy of universals. But all these were in fact posterior to the doctrines of morals; and disquisitions on beauty, the principles of taste, the precepts of rhetoric and criticism, were the last additions to the study of the phenomena of mind. And now, since the world seems to have acquiesced in the mode of investigation of general laws by experiment and observation, and to agree that this is all the knowledge which we can acquire of any subject whatever, it is to be expected that this branch of philosophical discussion will attain the same degree of im- The occupations, however, of ordinary life have often directed our efforts towards material objects, and engaged our attention on their properties and relations; and as all sciences have arisen from arts, and were originally implied in the maxims and precepts of those arts, until separated from them by the curious speculativeist, the knowledge of the material system of nature was possessed in detached scraps by the practitioners in the various arts of life long before the natural philosopher thought of collecting them into a body of scientific doctrines. But there have not been wanting in all ages men of curiosity, who, having been struck by the uniformity of the operations of nature in the material world, were eager to discover their causes. Accordingly, whilst the moralists and metaphysicians turned their whole attention to the phenomena of mind, and produced the sciences of pneumatology, logic, ethics, jurisprudence, and natural theology, these observers of nature found sufficient employment in considering the phenomena of the material world.

The bodies of which it consists are evidently connected by means of those properties by which we observe that they produce changes in each other's situations. This assemblage of objects may therefore be justly called a system. We may call it the material system. It is frequently termed nature; and the terms natural appearances, natural causes, natural laws, have been generally restricted to those which take place in the material system. This restriction, however, is improper, because there is no difference in the manner in which we form our notions of those laws, and reason from them, with respect both to mind and to body; or if there is to be any restriction, and if any part of the study of the universe is to be excluded in the application of these terms, it is that part only which considers moral obligation, and rather treats of what ought to be than of what actually is. As has already been observed, there is a considerable difference in the language which must be employed; but still there is none in the principles of investigation. We have no proof for the extent of any moral law but an appeal to the feelings of the hearts of men, indicated by the general laws or facts which are observed in their actions.

But this is only a question of the propriety of language. And no great inconvenience would arise from the restriction now mentioned if it were scrupulously adhered to; but unfortunately this is not always the case. Some authors use the term natural law to express every coincidence of fact; and this is certainly the proper use of the term. The French writers generally use the term loi physique in this enlarged sense. But many authors, misled by, or taking advantage of, the ambiguity of language, after having established a law founded upon a copious and perhaps unexpected induction of the phenomena of the material system (in which case it must be considered in its restricted sense), have, in their explanation of phenomena, extended their principle much farther than the induction on which they had founded the existence of the physical law. They have extended it to the phenomena of mind, and have led their followers into great and dangerous mistakes. Languages, like every other production of human skill, are imperfect. They are deficient in terms, and are therefore figurative. The most obvious, the most frequent, and the most interesting uses of language, have always produced the appropriate terms, and the progress of cultivation has never completely supplied new ones. There are certain analogies or resemblances, or certain associations of ideas, so plain that a term appropriated to one very familiar object will serve to suggest another analogous to it, when aided by the concomitant circumstances of the discourse; and this with sufficient precision for the ordinary purposes of social communication, and without leading us into any considerable mistakes; and it is only the rare and refined disquisitions of the curious speculativeist that bring the poverty and imperfection of language into view, and make us wish for words as numerous as our thoughts. There is hardly a sentence, even of common discourse, in which there are not several figures either of single words or of phrases; and when very accurate discrimination is required, it is almost impossible to find words or phrases to express distinctions which we clearly feel. We believe it impossible to express, by the scanty vocabulary of the Hebrews, the nice distinctions of thought which are now familiar to the European philosopher. In nothing does this imperfection of language appear so remarkably as in what relates to mind. Being a late subject of separate discussion, and interesting only to a few speculativeists, we have for it no appropriate vocabulary; and all our disquisitions concerning its operations are in continual metaphor or figure, depending on very slight analogies or resemblances to the phenomena of the material world. This renders the utmost caution necessary; and it justifies the British philosophers, who have been the most successful in prosecuting the study of the intellectual system, for having, almost without exception, restricted the terms natural laws, natural causes, natural philosophy, and such like, to the material system. With us pneumatology forms no part of physics. And we may venture to affirm, that the sciences have fared better by the restriction of the terms. In no country has the spirit of liberal discussion been more encouraged and indulged than in Britain, and her philosophers have been equally eminent in both branches of science. Their performances in ethics, jurisprudence, and natural theology, are considered by all our neighbours as the fountains of knowledge upon these subjects; and Locke and Clarke are names not less familiar on the continent than that of Newton.

Physics, then, is with us the study of the material system, including both natural history and philosophy. The term is not indeed very familiar in our language; and instead of physicus and disciplina physicae, we more generally employ the terms naturalist and natural knowledge. The term natural philosophy, in its common acceptation, is of British extent. The field of physical investigation is still of prodigious extent; and its different quarters require very different treatment, make very different returns, and accordingly have engaged in their particular cultivation persons of very different talents and tastes. It is of some importance to perceive the distinctions, and to see how the wants and propensities of men have led them into the different paths of investigation; for, as has been more than once observed, all sciences have sprung from the humble arts of life, and both go on improving by means of a close and constant correspondence.

All the phenomena of the material system may be arranged into two classes, distinguished both by their objects and by the proper manner of treating them. The first class comprehends all the appearances which are exhibited in the sensible motions of bodies, and their actions on each other producing sensible motion. The second class comprehends the appearances which are exhibited in the invisible motions and actions of the invisible particles of matter.

Of the phenomena of the first class we have examples in the planetary motions, the motions of heavy bodies, the phenomena of impulse, the motions and actions of machines, the pressure and motions of fluids, the sensible actions of magnetical and electrical bodies, and the motions of light. We have examples of the second class in the phenomena of heat and mixture, those exhibited in the growth of animals and vegetables, and many phenomena Thus it appears that there is a distinction in the phenomena sufficiently great to warrant a division of the study, and to make us expect a more rapid improvement by this division. Nay, the division has been made by nature itself; in the acquaintance which men have attained with her operations without study, before science appeared, and whilst art constituted all our knowledge.

Before man had recourse to agriculture, as the most certain means of procuring subsistence, our acquaintance with external substances was principally that of the natural historian; consisting of a knowledge of their fitness for food, medicine, or accommodation, their places of growth or habitation, and the means of procuring them, depending upon their manner of life or existence. It required a studied attention to these circumstances to give rise to agriculture, which therefore generally made its appearance after men had been in the practice of keeping flocks; by which means they were more at their ease, and had some leisure to attend to the objects around them, and in particular to those circumstances of soil and weather which affected the growth of their pasture.

When agriculture and a rude medicine were thus established, they were the first arts which had their foundation in a system of laws, by which the operations of nature were observed to be regulated; and with these arts we may begin the general study of nature, which was thus divided into two different branches. The rude physician would at first be a collector of specifics; but by degrees he would observe resemblances amongst the operations of his drugs, and would class them according to these resemblances. He would thus come to attend less to the drug than to its mode of operation; and would naturally speculate concerning the connection between the operation and the economy of animal life. His art now became a scientific system, connected by principle and theory, all proceeding upon the observation of changes produced by one kind of matter on another, but all out of sight. The frequent recourse to the vegetable kingdom for medicines would cause him to attend much more minutely to the few plants which he had occasion to study than the husbandman can do to the multitude which he is obliged to rear. The physician must learn to think, the husbandman to work. An analogy between the economy of animal and vegetable life could hardly fail to engage the attention of the physician, and would make him a botanist, both as a classifier of plants and as a philosopher.

He would naturally expect to unite the services of his drugs by combining them in his recipes, and would be surprised at his disappointments. Curious and unexpected changes would frequently occur in his manipulations: the sensible qualities, and even the external appearances, of his simples, would be often changed and even inverted by their mixture; and their medicinal properties would frequently vanish from the compound, and new ones be induced. These were curious, and to him interesting facts; and he would naturally be inquisitive after the principles which regulated these changes. His skill in this would by degrees extend beyond the immediate use for the knowledge of them; and the more curious speculative would lay the foundations of a most extensive and important science, comprehending all the phenomena of heat and mixture.

Along with this, and springing from the same source, another science must arise, contemplating the appearances of animal and vegetable life, and founded upon a careful observation and accurate description of the wonderful machine. The most inquisitive of men have in all ages been affected by the displays of wisdom and contrivance in the bodies of animals, and immediately engaged in investigation into the uses and functions of their various parts and organs. The phenomena have been gradually discriminated, and arranged under the various heads of nutrition, conception, secretion, absorption, assimilation, rejection, growth, life, decay, disease, and death; and, in conformity to the doctrines which have with greater or less evidence been established on these subjects, the action of medicines, and the whole practice of physic and surgery, has been established in the form of a liberal or scientific art.

The husbandman, in the mean time, must till or labour the ground which lies before him. He, too, is greatly interested in the knowledge of the vegetable economy, and knowledge forms some systems on the subject by which he regulates his labours; but he sees, that whatever is the nature of vegetable life, he must work hard, and he searches about for everything which can tend to diminish his labour. The properties of the lever, the wedge, and the inclined plane, soon become familiar to him; and, without being able to tell on what their efficacy depends, he uses them with a certain sagacity and effect. The strength of timber, the pressure and force of water, are daily seen and employed by him and other artisans who labour for their mutual accommodation; and some rude principles on these subjects are committed to memory. Many tools and simple machines are by this time familiar; and thus the general properties of matter, and the general laws of the actions of bodies upon each other, become gradually matter of observation and reflection; and the practical mechanic will be frequently improving his tools and machines. The general aim is to produce a greater quantity of work by the same amount of exertion. The attempts at improvement will be awkward, and frequently unsuccessful. When a man finds, that by increasing the length of his lever he increases his power of overcoming a resistance, a small degree of curiosity is sufficient to make him inquire in what proportion his advantage increases. When he finds that a double length gives him a double energy, he will be surprised and mortified to find, that at the end of the day he has not performed twice the quantity of work; but, after much experience, he will learn that every increase of energy, by means of a machine, is nearly compensated by an increase of time in the performance of his task; and thus one of the great and leading principles of practical mechanics is inculcated in a manner not to be forgotten, and the practical mechanic brought to speculate about motion and force; and by gradual and easy steps the general laws of simple motions are established.

It is evident that these speculations cannot be carried on, nor any considerable knowledge acquired, without some acquaintance with the art of measurement; and the very questions which the mechanic wishes to solve presuppose some advances in this art, which in process of time refined itself into mathematics, the most perfect of all the sciences. All the phenomena of sensible motion afford employment to the mathematician. It is performed in a double or triple time, through a double or triple space, by a double or triple body, by the exertion of a double or triple force; produces a double or triple effect; is more to the right or to the left, upwards or downwards, &c.; in short, every affection of motion is an object of mathematical discussion. Such a science must have ere now appeared in the form of an art, in consequence of the mutual transactions of men. These amongst an uncultivated people are chiefly in the way of barter. If I want corn from a peasant, and have nothing to give for it but the cloth which I have made, we must fall on some way of adjusting our terms in respect of the quantity. We should soon discover that the length, and breadth, and depth of the box or bag were equally important; and it would not be difficult to see, that if any of them were doubled or tripled, the quantity of grain would be so too; if two of them were doubled, the grain would be quadrupled; and if all the three were doubled the quantity of grain would be increased eight times. The same thing would also be observed with respect to my cloth. By such transactions as these, a few of the properties of plane and solid numbers and figures would become known, and the operations of multiplication and division, where arithmetic is combined with geometry; and daily observation shows us, that the more abstruse properties of number and figure, which to the generality of mankind are so insignificant, lay hold on the fancy of some individuals with such force, as to abstract them from every other intellectual entertainment, and they are studied with a keenness and perseverance almost unequalled in any other walk of science. To most men the performance of a machine is a more attractive object than the properties of a figure, and the property of a figure more entertaining than that of a number; but the fact seems to be otherwise. Before Pythagoras had invented the theorem which bears his name, and which is amongst the first elements of geometry, he had reformed the Grecian music by the addition of a note to their scale; and this addition proceeds on a very refined speculation respecting the properties of numbers. Hence amongst the Greeks arithmetic must have made considerable progress, whilst geometry was yet in its cradle; and we know to what astonishing length they prosecuted the science of pure geometry, whilst their knowledge of mechanical principles was almost nothing. The Arabs also made hardly any addition to the geometry of the Greeks, if they did not rather almost completely forget it; whilst they improved their arithmetic into algebra, the most refined and abstract branch of human knowledge. There is such a distance, in point of simplicity, between pure mathematics and the most elementary mechanics, that the former continued to make rapid steps to improvement in more modern times, whilst the latter languished in its infancy, and hardly deserved the name of science till latterly, when the great demand for it, by the increase and improvement in manufactures, interested many in the study, and facilitated its progress, by the multitude of machines which were contriving on all hands by the manufacturers and artisans; and even at present it must be acknowledged, that it is to them that we are indebted for almost every new invention in mechanics, and that the speculative has seldom done more than improve the invention, by exhibiting its principles, and thus enabling the artist to correct its imperfections; and now science and art go hand in hand, mutually giving and receiving assistance. The demands of the navigator for mathematical and astronomical knowledge have dignified these sciences; and they are no longer the means of elegant amusement alone, but merit the munificence of princes, who have erected observatories, and furnished voyages of discovery, where the mathematical sciences are at the same time cherished, and applied to the most important purposes.

This short sketch of what may be called the natural history of the physical sciences will not, we hope, be thought improper or unprofitable. It tends to confirm an assertion often alluded to, that the prosecution of the study of nature will be more successful, if we imitate her mode of proceeding, and divide the labour. It will be still further confirmed by attending to the scientific difference of the phenomena, which marks out a different mode of proceeding, and a difference in the knowledge which we shall ultimately acquire, after our most successful researches.

In both classes of phenomena already distinguished, we must grant, that the principle which connects the pairs of concomitant events, rendering the one the inseparable companion of the other, is totally unknown to us, because it is not the immediate object of our perception. But in the phenomena of the first class, we see the immediate exertion of this principle, whatever it may be; we can observe the exertion with accuracy; we can determine its kind and degree, which are the signs and measures of the kind and degree of the unperceived cause. This exertion, being always some modification of motion, allows us to call in the aid of mathematical knowledge, and thus to ascertain with the precision peculiar to that science the energy of the cause, judging of the tendency and quantity by the tendency and the quantity of the observed effect. But in the second class of phenomena the case is very different. In the operations of chemistry, for instance, the immediate exertion of the cause is not perceived; all that we observe is the assemblage of particles which obtains before mixture, and that which takes place when it is completed, and which we consider as its result. The procedure of nature in producing the change is unseen and unknown. The steps are hid from our observation. We are not only ignorant of the cause which determines one particle of our food to become a part of our body whilst others are rejected, but we do not see the operation. We are not only ignorant of the cause which determines a particle of vitriolic acid to quit the fossil alkali with which it is united in Glauber's salt, and to attach itself to a particle of magnesia already united with the muriatic acid, which also quits it to unite with the alkali; but we do not see the operation. The particles and their motions are not the objects of our senses; and all that we see is the Epsom salt and common salt separated from the water in which we had formerly dissolved the sal mirabile and the muriated magnesia. The motions, which are the immediate effects of the changing causes, and therefore their only indications, characteristics, and measures, fitted to show their nature, are hidden from our view.

Our knowledge therefore of these phenomena must be less perfect than that of the phenomena of the former class; and we must here content ourselves with the discovery of more remote relations and remote causes, and with our ignorance of the very powers of nature by which these changes are brought about, and which are cognoscible only by their immediate effects, namely, the motions which they produce unseen. The knowledge which we really do acquire is somewhat similar to what the mechanical philosopher has acquired when he has discovered, by many experiments and investigations, that magnets attract each other by their dissimilar, and repel each other by their similar poles, and do not act at all upon any bodies except leadstones and iron. Here we leave undiscovered all that is most curious in the phenomenon, namely, how these attractions and repulsions are produced; and even here the magnetical philosopher has the advantage of seeing the agents and the operation.

But philosophers attending to this circumstance, that, even in these cases, the changes are produced by motions, or consist in motions, however unperceived these may be, have concluded, that the laws according to which nature operates in producing these changes are similar to the laws which regulate her operations in the sensible actions of the bodies, or are included in them; and that the motions, although unseen, and the moving forces, are perfectly similar. They have therefore employed similar modes of investigation, applying the laws of impulse, and calling in the aid of mathematical knowledge. Of this we have many examples in the writings of Dr Freind, Keill, Bernoulli, Helsham, Boerhaave, Hartley, and others, who have delivered theories of fermentation, solution, precipitation, crystallization, nutrition, secretion, muscular action, nay, even of sensation and intelligence, founded, as they think, upon the laws of motion, and illustrated and supported by mathematical reasoning. Lord Bacon himself, that careful and sagacious distinguisher of intellectual operations, has gone into the same track in his explanation of the phenomena of fire and combustion; and Sir Isaac Newton has made several attempts of the same kind, although with peculiarities which always characterize his discussions. and render them very different from those of an inferior class.

But the success of these philosophers has hitherto been very discouraging; indeed they had no title to expect any; for their whole trains of reasoning have proceeded upon analogies which were not observed, but assumed or supposed without any authority. There is not that similarity in the phenomenon, or in the visible effect, which is absolutely necessary for a successful reasoning by analogy. We do not observe any local motion, any change of place, which alone enables us to reason mathematically on the subject. And to render the case desperate, this ill-founded analogy has been mixed with hypotheses completely gratuitous. Certain forms have been assigned to the particles, and certain modes of action have been laid down for them, for the reality of which we have not the least argument or indication; and, to complete the matter, these fancied forms and laws of action have been such as are either self-contradictory and inconsistent, or they have been such as, if allowed to act in a way analogous to what we observe in the sensible motions of bodies, would produce effects totally different from those which are observed. These atomical theories, as they are called, transgress every rule of philosophical discussion; and even the best of them are little better than trifling amusements. By far the greatest part of them only serve to raise a smile of pity and contempt in every person who is at all acquainted with mechanical philosophy. Whenever we see an author attempting to explain these hidden operations of nature by invisible fluids, by ethers, by collisions, and vibrations, and particularly if we see him introducing mathematical reasonings into such explanations, the best thing we can do is to shut the book, and take to some other subject. That we may not be thought to speak presumptuously upon this occasion, we only beg leave to remind our readers, that the united knowledge of the most eminent mathematicians of Europe has not yet been able to give anything more than an approximation to the solution of the problem of three bodies, that is, to determine with accuracy the motions of three particles of matter acting on each other in the simplest of all possible manners, viz. by forces varying as the squares of the distances inversely; and the vibrations of elastic bodies, of any but the very simplest possible forms, are to this day beyond the reach of investigation. What then should be our expectations in cases where millions of particles are acting at once, of forms unobserved, and with forces unknown, and where the object is not a determination of an average result of many, where the precise state of an individual article need not be known, but where it is this very precise state of each single particle that we want to know? What can it be but uncertainty and mistake?

Notwithstanding these discouraging circumstances, we must observe that this kind of inquiry has greatly improved, amongst with the improvement and extension of mathematical philosophy, and since philosophers have given over their incessant attempts to explain everything by impulse; and we need not despair of making still further advances, if we will content ourselves with going no farther than Newton has done in his explanation of the planetary motions. He has immortalized his own name, and has added immensely to our stock of useful knowledge; yet he has stopped short at the discovery of the fact of universal gravitation; and all who have endeavoured to explain or account for this fact have only exposed themselves to pity. We may perhaps be one day able to demonstrate from the phenomena that the particles of matter have certain mutual tendencies to or from each other, exerted according to fixed or invariable rules; and from these tendencies we may be able to explain many other phenomena, and predict the consequences, with as much certainty and evidence as an astronomer calculates a future eclipse. This Mechanical Philosophy would be a great acquisition, and perhaps more is impossible; and the road to this has been indicated by Sir Isaac Newton, who has expressed his suspicion, that as the great movements of the solar system are regulated by universal gravitation, so the mutual actions of the particles of matter are produced and regulated by tendencies of a similar kind, equally but not more inexplicable, and of which the laws of action are to be discovered by as careful an attention to the phenomena, and by the same patient thinking, which he has employed on the planetary motions.

The above distinction in the nature of the phenomena, the difference in the nature of the knowledge which is to be acquired, and the means which are to be employed for the successful prosecution of the two branches of general physics, have occasioned a still farther restriction (at least in Britain) of the term Natural Philosophy. It is particularly applied to the study of the phenomena of the first class, whilst those of the second have produced the sciences of Chemistry and Physiology.

The phenomena of the first class have been usually called mechanical, in order to distinguish them from those observed in the operations of chemistry, and in the animal and vegetable economy; and the explanations which have been attempted of some of the last, by applying the laws observed in the phenomena of the first class, have been called mechanical explanations.

As this first class is evidently but a part of general physics, there is some impropriety in giving the name natural philosophy to a course of doctrines which is confined to these alone. Indeed at the first institution of universities, the lectures given in the Schola Physica were much more extensive, comprehending almost all the phenomena of the material world; but as all arts and sciences have improved most where the labour has been most divided, it was found more conducive to the advancement of knowledge that separate institutions should be founded for the studies of natural history, chemistry, physiology, &c.; and thus the phenomena, purely mechanical, and a few others in magnetism, electricity, and optics, which either were susceptible of mathematical treatment, or had little connection with the studies of chemistry and physiology, were left to the care of the professor of natural philosophy.

As the terms chemistry and physiology have been applied to two very important branches of general physics, we think that a more specific or characteristic name might be appropriated to the other, and that it might very properly be termed Mechanical Philosophy.

It only remains to make a few observations on the distinctive means of prosecuting these studies with success; and to point out some of the advantages which may reasonably be expected from a careful prosecution of them; but in doing so, we shall confine ourselves to what is usually called Natural Philosophy, referring generally to the articles Chemistry and Physiology for what belongs to these branches.

Mechanical Philosophy may, in conformity with the foregoing observations, be defined, the study of the sensible motions of the bodies of the universe, and of their actions producing sensible motions, with the view to discover their causes, to explain subordinate phenomena, and to improve art.

The principle upon which all philosophical discussion proceeds is, that every change which we observe in the condition of things is considered by us as an effect, indicating the agency, characterizing the kind, and measuring the degree of its cause. In the language of mechanical philosophy, the cause of any change of motion is called a moving or changing force. The disquisitions of natural philosophy must therefore begin with the consideration of Mechanical motion, carefully noticing every affection or quality of it, so as to establish marks and measures of every change of which it is susceptible; for these are the only marks and measures of the changing forces. This being done, it only remains to apply them to the motions which we observe in the universe.

From the general principle of philosophical discussion already mentioned, there flow directly two axioms. 1. Every body perseveres in a state of rest, or of uniform rectilinear motion, unless affected by some moving force. 2. Every change of motion is in the direction and in the degree of the force impressed. These are usually called the laws of motion. They are more properly laws of human judgment with respect to motion. Perhaps they are necessary truths, unless it be alleged that the general principle, of which they are necessary consequences, is itself a contingent though universal truth. By these two axioms, applied in abstracto to every variety of motion, we establish a system of general doctrines concerning motions, according as they are simple or compounded, accelerated, retarded, rectilineal, curvilineal, in single bodies, or in systems of connected bodies; and we obtain corresponding characteristics and measures of accelerating or retarding forces, centripetal or centrifugal, simple or compound.

We have an illustrious example of this abstract system of motion and moving forces in the first book of Sir Isaac Newton's Mathematical Principles of Natural Philosophy. Euler's Mechanica sine Scientia Motus, Herman's Phoronomia sive de Viribus Corporum, and D'Alembert's Traité de Dynamique, are also excellent works of the same kind. In this abstract system no regard is paid to the casual differences of moving forces, or the sources from which they arise. It is enough to characterize a double-accelerating force, for instance, that it produces a double acceleration. It may be a weight, a stream of water, the pressure of a man; and the force of which it is said to be double may be the attraction of a magnet, a current of air, or the action of a spring.

Having established these general doctrines, the philosopher now applies them to the general phenomena of the universe, in order to discover the nature of the forces which really exist, and the laws by which their operations are regulated, and to explain interesting but subordinate phenomena. This is the chief business of the mechanical philosopher; and it may with some propriety be called the mechanical history of nature.

Some method must be followed in this history of mechanical nature. The phenomena must be classed by means of their resemblances, which infer a resemblance in their causes; and their classes must be arranged according to some principle. We have seen no method which appears to us less exceptionable than the following.

The principle of arrangement is the generality of the phenomena; and the propriety of adopting this principle arises from the probability which it gives us of more readily discovering the most general actuating forces, whose agency is implicated in all other phenomena of less extent, and therefore should be previously discussed, that we may detect the discriminating circumstances which serve to characterize the subordinate phenomena, and are thus the marks of the distinguishing and inferior natural powers.

The most general of all phenomena is the curvilineal motion of bodies in free space; it is observed throughout the whole extent of the solar system. The mechanical history of nature begins therefore with astronomy. Here, from the general phenomena of the planetary motions, is evinced the fact of the mutual deflection of every body towards every other body, and this in the inverse proportion of the squares of the distance, and the direct proportion of the quantity of matter. This is the fact of universal gravitation, indicating the agency, and measuring the intensity, of the universal force of mutual gravity.

Having established this as an universal fact, the natural philosopher proceeds to point out all the particular facts which are comprehended under it, and the peculiarities of which characterize the different movements of the solar system. That is, in the language of philosophy, he gives a theory or explanation of the subordinate phenomena, the elliptical motions of the planets and comets, their mutual disturbances, the lunar irregularities, the oblate figure of the planets, the nutation of the earth's axis, the precession of the equinoxes, and the phenomena of the tides and trade winds; and he concludes with the theory of the parabolic motion of bodies projected on the surface of this globe, and the motion of pendulums.

As he goes along, he takes notice of the applications which may be made to the arts of life, of the various doctrines which are successively established; such as chronology, astronomical calculation, dialling, navigation, gunnery, and the measuring of time.

If a square parcel of sand be lying upon the table, and the finger be applied to any part of it to push it along the table, that part is removed where you will, but the rest remains in its place; but if it be a piece of sand-stone of the same materials and shape, and the finger be applied as before, the whole is moved, and the other parts accompany the part impelled by the finger in all its motions. From the moon's accompanying the earth in all its motions round the sun, we infer a moving force which connects the moon and earth. In like manner we must conclude, that a moving force connects the particles of the stone; for we give the name force to everything which produces motion. We call it the force of cohesion, a term which, like gravitation, expresses merely a fact. This seems to be the next phenomenon of the universe in point of extent.

Having, from the general phenomenon, established the existence of this force, the philosopher proceeds to ascertain the laws by which its exertions are regulated; which is the ascertaining its distinctive nature and properties. This he does in the same way that he ascertained the nature of planetary gravitation, namely, by observing more particularly the various phenomena. Here is opened a most extensive and varied field of observation, in which it must be acknowledged that very little regular and marked progress has been made. The variety of the phenomena, and the consequent variety in the nature of the connecting forces, appear as yet inconceivably great; and there seems little probability of our being able to detect in them all any sameness, combined with the other distinguishing circumstances, as we have done in the case of gravity. Yet we should not despair. Boscovich has shown, in the most unexceptionable manner, that although we shall suppose that every atom of matter is endowed with a perfectly similar force, acting in a certain determined ratio of the small and imperceptible distances at which the particles of matter are arranged with respect to each other, the external or sensible appearances may, and must, have all that variety which we observe. He also shows very distinctly how, from the operation of this force, must arise some of the most general and important phenomena which characterize the different forms of tangible bodies.

We observe the chief varieties of the action of this corpuscular force upon the bodies which we denominate hard, soft, solid, fluid, vaporous, brittle, ductile, elastic. We see instances where the parts of bodies avoid each other, and require external force to keep them together, or at certain small distances from each other. This is familiar in air, vapours, and all compressible and elastic bodies, and is evidently a most curious and interesting subject of investigation. On the nature and action of these corpuscular forces depend the strength or firmness of solids, their ela- their power of communicating motion, the pressure, and motion, and impulse of fluids; nay, on the same actions depend all the chemical and physiological phenomena of expansion, fusion, congelation, vaporisation, condensation, solution, precipitation, absorption, secretion, fermentation, and animal and vegetable concoction and assimilation. Out of this immense store of phenomena, this inexhaustible fund of employment for our powers of investigation, the natural philosopher selects those which lead directly to the production or modification of sensible motion.

He will therefore consider, firstly, the communication of motion amongst detached and free bodies, establishing the laws of impulse or collision. This has always been considered as the elementary doctrine of mechanical philosophy, and as the most familiar fact observed in the material world; and in all ages philosophers have been anxious to reduce all actions of bodies upon each other to impulse, and have never thought a phenomenon completely explained or accounted for until it had been shown to be a case of impulse. This it is which has given rise to the hypotheses of vortices, ethers, magnetic and electric fluids, animal spirits, and a multitude of fancied intermediaries between the sensible masses of matter, which are said in common language to act upon each other. A heavy body is supposed to fall, because it is impelled by a stream of an invisible fluid moving according to certain conditions suited to the case. The filings of iron are supposed to be arranged round a magnet by means of a stream of magnetic fluid issuing from one pole, circulating perpetually round the magnet, and entering at the other pole, in the same manner as we observe the flote-grass arranged by the current of a brook.

But the philosopher who has commenced the mechanical study of nature by the abstract doctrines of dynamics, and made its first application to the celestial phenomena, and who has attended carefully to the many analogies between the phenomena of gravitation and cohesion, will be at least ready to entertain very different notions of this matter. He will be so far from thinking that the production of motion by impulse is the most familiar fact in nature, that he will acknowledge it to be comparatively very rare; nay, there are some appearances in the facts, which are usually considered as instances of impulsion, which will lead him to doubt, and almost to deny, that there has ever been observed an instance of one body putting another in motion by coming into absolute contact with it, and striking it; and he will be disposed to think that the production of motion in this case is precisely similar to what we observe when we gently push one floating magnet towards another, with their similar poles confronting each other. There will be the same production of motion in the one and diminution of it in the other, and the same uniform motion of the common centre of gravity: and, in this case of the magnets, he sees completely the necessity of a law of motion, which is not an axiom, but is observed throughout the whole of nature, and which receives no explanation from any hypothesis of an intervening fluid, but is even totally inconsistent with such a supposition. We mean, "that every action of one body on another is accompanied by an equal and opposite action of that other on the first." This is usually called the equality of action and re-action. It is not intuitive, but it is universal; and it is a necessary consequence of the perfect similarity of the corpuscular forces of the same kinds of matter. This general fact, unaccountable on the hypothesis of impelling fluids, is considered in the planetary motions as the unequivocal indication of the sameness of that gravity which regulates them all. The rules of good reasoning should make us draw the same conclusion here, that the particles of tangible matter are connected by equal and mutual forces, which are the immediate causes of all their sensible actions, and that these forces, like gravitation, vary with every change of distance and situation.

The laws of collision and impulsion being now established, either as original facts, or as consequences of the agency of equal and mutual forces which connect the particles of matter, the philosopher considers, secondly, the production specta of motion by the intervention of solid bodies, where, by reason of the cohesion of matter, some of the motions are necessarily confined to certain determinate paths or directions. This is the case in all motions round fixed points or axes, or along planes or curves which are oblique to the action of the forces.

This part of the study contains the theory of machines, pointing out the principles on which their energy depends, and consequently furnishing maxims for their construction and improvement. But these observations do not complete the discussion of the mechanism of solid bodies. They are not only solid and inert, but they are also heavy; and therefore the action of gravity must be combined with the consequences of solidity. This will lead to discussions about the centre of gravity, the theory and construction of arches and roofs, the principles of stability and equilibrium, the attitudes of animals, and many particulars of this kind.

Thirdly, the philosopher will now turn his attention to another form in which tangible matter exhibits many interesting phenomena, namely, fluidity. The first thing to be attended to here is, What is that particular form of existence? What is the precise phenomenon which characterizes fluidity? What is the definition of a fluid? This is by no means an easy question, and considerable objections may be stated against any definition that has been given of it. Sir Isaac Newton says, that a fluid is a body whose particles yield to the smallest impression, and by so yielding are easily moved amongst themselves. It may be doubted whether this be sufficiently precise; what is meant by the smallest impression? and what is easily moving? Is there any precise degree of impression to which they do not yield; and do they oppose any resistance to motion? And a still stronger objection may be made. It is not clear that a body so constituted will exhibit all the appearances which a body acknowledged to be fluid does really exhibit. Euler offers some very plausible reasons for doubting whether it will account for the horizontal surface, and the complete propagation of pressure through the fluid in every direction; and therefore prefers selecting this last phenomenon, the propagation of pressure quaqua versus, as the characteristic of fluidity, because a body having this constitution (on whatever circumstance it may depend) will have every other observed property of a fluid. But this definition is hardly simple or perspicuous enough; and we think that the objections against Newton's more simple and intelligible definition are not unanswerable. Boscovich defines a fluid to be a body whose particles exert the same mutual forces in all directions, and shows that such particles must be indifferent, as to any position, with respect to each other. If no external force act upon them, they will remain in every position, and will have no tendency to arrange themselves in one position rather than another; differing in this respect from the particles of solid, or soft, or viscid bodies, which require some force to change their respective positions, and which recover these positions again when but gently disturbed. He illustrates this distinction very beautifully, by comparing a parcel of balls thrown on quicksilver, and attracting each other, with a parcel of magnets in the same situation. The balls will stick together, but in any position; whereas the magnets will always affect a particular arrangement.

When the characteristic phenomenon of fluidity has been selected, the philosopher proceeds to combine this pro- Mechanical perty with gravity, and establishes the doctrine of hydro- statics, or of the pressure and equilibrium of heavy fluids; and the propagation of this pressure in every direction; and demonstrates the horizontality of surface assumed by all perfect fluids. These doctrines and principles enable us to determine several very interesting circumstances re- specting the mutual pressure of solids and fluids on each other, such as the pressures exerted on the bottoms and sides of vessels, and the support and whole mechanism of floating bodies.

He then considers how fluids will move when their equilibrium of pressure is destroyed; and establishes the doctrines of hydraulics, containing all the modifications of this motion, arising from the form of the vessels, or from the intensity or direction of the pressure which occasions it. And this subject is completed by the consideration of the resistance which fluids oppose to the motion of solid bodies through them, and their impulse on bodies opposed to their action. These are very important matters, being the foundations of many mechanical arts, and furnishing us with some of our most convenient and efficacious powers for impelling machines. They are also of very difficult discus- sion, and have by no means been completely investigated or established. Much remains yet to be done, both for per- fecting the theories, and for improving the arts which de- pend upon them.

It is evident that upon these doctrines depend the know- ledge of the motions of rivers and of waves; the buoyancy, equilibrium, and stability of ships; the motion of ships through the waters; the action of the winds on the sails; and the whole arts of marine construction and seamanship.

There is another general form of tangible matter which exhibits very different phenomena, which are also ex- tremely interesting; we mean that of vapour. A vapour is a fluid, and all the vapours that we know are heavy fluids; they are therefore subject to all the laws of pres- sure and impulse. But they are susceptible of great com- pression by the action of external forces, and expand again when these forces are removed. In consequence of this compression and expansion, the general phenomena of flu- idity receive great and important modifications; and this class of fluids requires a particular consideration. As air is a familiar instance, this branch of mechanical philosophy has been called pneumatics.

Under this head we consider the pressure of the atmo- sphere, and its effects both on solid and on fluid bodies. It produces the rise of waters or other fluids in pumps and syphons, and gives us the theory of their construction. It explains many curious phenomena of nature, such as the motions in the atmosphere, and their connection with the pressure of the air, and its effect upon the barometer or weather-glass. Air, when in motion, is called wind; and it may be employed to impel bodies. The theory of its action, and of its resistance to moving bodies, is therefore to be considered in this place.

But besides their motions of progression, &c., such as we observe in winds, compressible or elastic fluids are suscep- tible of what may be termed internal motion; a kind of undulation, where the contiguous parts are thrown into tremulous vibrations, in which they are alternately con- densed and rarefied; and these undulations are propagated along the mass of elastic fluid, much in the same way in which we observe waves to spread on the surface of wa- ter. What makes this an interesting subject of considera- tion is, that these undulations are the more ordinary causes of sound. A trembling chord, or spring, or bell, agitates the air adjoining to it. These agitations are propagated along the air, and by its intervention agitate the organ of hearing. The mechanism of these undulations has been much studied, and furnishes a very beautiful theory of musical harmony.

The philosopher examines the law of compressibility of Me- chanical air and other elastic fluids, and thus gets the knowledge of the constitution of the atmosphere, and of the action of those fluids when employed to impel solid bodies. Gun- powder contains an immense quantity of permanently clas- tic air, which may be set at liberty by inflammation. When this is done at the bottom of a piece of ordnance, it will impel a ball along the barrel, and discharge it from the muzzle, in the same way that an arrow is impelled by a bow. And thus having discovered in what degree this air presses in proportion to its expansion, we discover its ac- tion on the ball throughout the whole length of the piece, and the velocity which it will finally communicate to the ball. Here then is contained a theory of artillery and of mines.

Chemistry teaches us, that most bodies can be convert- ed by fire into elastic fluids, which can be employed to act upon other bodies in the way of pressure or impulse. Thus they come under the review of the mechanical phi- losopher; and they have become interesting by being em- ployed as moving forces in some very powerful machines.

These discussions will nearly exhaust all the general me- chanical phenomena. There remain some, however, which are much more limited, but furnish very curious and im- portant subjects of investigation.

The phenomena exhibited between loadstones or mag- nets and iron have long attracted attention; and the use to which the polarity of the loadstone has been applied, namely, the directing the course of a ship through the pathless ocean, has rendered these phenomena extremely interesting. They are specified by the term magnetism.

Considerable progress has been made in the arrange- ment and generalization of them; but we have by no means been able hitherto to bring them all under one simple fact or law. The attention has been too much turned to the dis- covery of the ultimate cause of magnetism; whereas we should have rather employed our ingenuity in discovering all the general laws, in the same manner as Kepler and Newton did with respect to the celestial phenomena, with- out troubling themselves with the cause of gravitation.

Dr Gilbert of Colchester was the first who considered the magnetical phenomena in a truly philosophical manner; and his treatise De Magnete may be considered as the first, and one of the most perfect specimens of inductive logic. It is indeed an excellent performance; and when we consider its date, 1580, it is almost a wonder. Epinus's Tentamen Theoriae Magnetismi is a most valuable work, and contains nearly all the knowledge which we have as yet of the subject.

There is another class of mechanical phenomena which have a considerable affinity with the magnetical; we mean the phenomena called electrical. Certain bodies, when rubbed or otherwise treated, attract and repel other bo- dies, and occasion a great variety of sensible motions in the neighbouring bodies. Philosophers have of late years paid much attention to these appearances, and have esta- blished many general laws concerning them. But we have not been more successful in bringing them all under one fact or law, and thus establishing a complete theory of them, than in the case of magnetism. Franklin and Epinus are the authors who have been most successful in this respect. Dr Franklin, in particular, has acquired great celebrity by his most sagacious comparison of the phenomena; which has enabled him to establish a few general laws, almost as precise as those of Kepler, and of equally extensive in- fluence. His discovery, too, of the identity of thunder and electricity has given an importance and dignity to the whole subject. There are many phenomena of electricity which cannot be called mechanical, and are of the most curious and interesting kind. As these have little con- nection with any of the other great branches of physical The appearances which are presented to us by our sense of seeing form another class, which has always been considered as forming a branch of natural philosophy in all seminaries of learning. It does not, however, obviously appear that they are mechanical phenomena. The intimate nature of light is still a secret. Fortunately it is not necessary to be known to give us a very perfect theory of the chief phenomena. The general laws of optics are so few, so simple, and so precise, that our theories are perhaps more perfect here than in any other branch of physics; but these theories are as yet far removed from the rank of primary facts. Many unknown events happen before the phenomenon comes under the hands of the ordinary optician, so as to become the subjects of the simple laws of reflection and refraction. It may even be doubted, and has been doubted, whether the phenomena of optics are cases of body in motion; whether all the lines which the optician draws are anything but the directions along which certain qualities are exerted. The side of a ball which is next the candle may be bright and the other side dark, just as the side of a ball which is next the electrical globe is minus and the other side plus; and all this without any intervening medium. Apparition or visibility may be a quality of a body, depending on the proximity and position of another body, without anything between them, just as weight is; and this quality may be cognizable by our faculty of seeing alone, just as the pressure of a heavy body is by our feeling alone.

The first thing which made it probable that mechanical philosophy had anything to do with the phenomena of optics, was the discovery of Mr Roemer, "that apparition was not instantaneous;" that some time elapsed between the illumination of a body and its being seen at a distance. He discovered that it was not till forty minutes after the sun illuminated one of Jupiter's satellites that it was seen by the inhabitants of this globe. If therefore a sun were just created, it would be forty minutes before Jupiter would be illuminated by him, and two hundred before the Georgian planet would be illuminated. Here then is motion. It is therefore highly probable that there is something moved; but it is still doubted whether this something, which we call light, is a matter emitted from the shining body, and moving with great velocity, and acting upon and affected by other bodies in the various phenomena of optics, or whether it is a certain state of a medium which is thus propagated, as we see that waves are propagated along the surface of water, or sonorous undulations through the mass of air, whilst the water or air itself is hardly moved out of its place. Either of these suppositions makes optics a legitimate branch of mechanical philosophy; and it is the philosopher's business to examine both by the received laws of motion, and to see which of them gives consequences which tally with the phenomena. This has been done; and we imagine that a complete incompatibility has been demonstrated between the consequences of the undulations of an elastic medium and the phenomena of optics, whilst the consequences of the other or vulgar notion on this subject are perfectly consistent with mechanical laws. There are some things in this hypothesis very far beyond our power to conceive distinctly; but they are all similar in this respect to many facts acknowledged by all, and there is no phenomenon that is inconsistent with the legitimate consequences of the hypothesis. This gives it great probability; and this probability is confirmed by many chemical facts, and by facts in the vegetable economy, which give strong and almost undeniable indications of light being a body capable of a chemical union with the other ingredients of sublunar bodies, and of being afterwards set at liberty under its own form, as the cause or medium of vision. But these are questions similar to those about the cause of gravity, and totally unnecessary for establishing a complete theory of the optical phenomena for explaining the nature of vision, the effects of optical instruments, the cause of colours, the phenomena of the rainbow, halos and parhelia, &c. Only all this theory is unconnected with the principles called mechanical.

Such is the field of observation laid open to the mechanical philosopher of the present day. We may hope to extend it, and by degrees apply its doctrines even to the unseen motions which take place in chemistry and physiology. But we must, in the first place, perfect our knowledge of the sensible motions and actions of bodies. Those of fluids still demand much investigation; and till these are thoroughly understood, it is not time to attempt penetrating further into the recesses of nature.

In the prosecution of this study, it is found that every change which can be observed in the state of a body, with respect to motion by the action of another body, is accompanied by an equal and opposite change in the state of that other body. Thus, in the phenomena of gravitation, it is observed that the deflections of the sun and planets to each other are mutual. The same thing is observed in the actions of magnets on each other and on iron; it is also observed in the attractions and repulsions of electrical bodies; and it also obtains in all the phenomena of impulse and of corporeal pressure. It is therefore an universal law of motion; that action is always equal and opposite to reaction; but this must be considered merely as a matter of fact, a contingent law of nature, like that of gravitation. The contrary is perfectly conceivable, and involves no contradiction. That this is so, is evident from the proceedings of philosophers, who in every new case make it their business to discover by experiment whether this law was observed or not. It was amongst the last discoveries made by Sir Isaac Newton in his examination of the celestial motions. This being the case, it should never be assumed as a principle of reasoning until its operation has been ascertained by observation. It has been owing to this improper procedure that much false reasoning has been introduced into mechanical philosophy, and more particularly into the theory of impulsion, or the communication of motion by impulse. In considering this subject, a term has been introduced which has occasioned much wrangling and misconception; we mean the term inertia. It serves indeed to abbreviate language, but it has often misled the judgment. When used with cautious attention to every circumstance, it expresses nothing but the necessity of a cause to the production of any effect; but it is generally used as expressing a quality inherent in matter, by which it resists any change of state, or by which it maintains its present state. Matter is said to be inert; and as everything which changes the motion of a body is called a force, and as the inertia of A is supposed to change the motion of B, it is called vis inertiae; and yet matter is said to be indifferent as to motion or rest, and to be inactive. These are surely very incongruous expressions. This obscure discourse has arisen from the poverty of all languages, which are deficient in original terms, and therefore employ figurative ones. Force, action, resistance, are all appropriated terms relating to our own exertions; and some resemblance between the external effects of these exertions and the effects of the connecting qualities of natural bodies, has made us use them in our disquisitions on these subjects. And as we are conscious that, in order to prevent our being pushed by another from our place, we must resist, exerting force; and that our resistance is the reason why this other man has not accomplished his purpose; we say, that the quiescent body resists being put in Mechanical motion, and that its inertia is discovered by the diminution made in the motion of the impelling body. And upon the authority of this vis inertiae as a first principle the phenomena of impulsion are explained, and the law of equal action and re-action is established.

But all this procedure is in contradiction to the rules of inductive logic; and the obscurity and confusion which have arisen from this original misconception, the consequent incongruity of language, and the awkward attempts that have been made to botch and accommodate it to the real state of things, have occasioned a dispute, and the only dispute, in natural philosophy, which has not yet been settled, and never can be settled, whilst such misconceptions are allowed to remain.

If the word inertia be taken as expressing, not a quality of matter, but a law of human judgment respecting matter, as expressing our necessity of inferring the agency of a moving force whenever we observe a change of motion, all difficulties will vanish, and the equality of action and re-action will be inferred, as it should be, from the phenomena of collision. There will be inferred a vis insita corpori impellenti, not qua movendi, but qua corpori; and this inference will carry us through all the mysteries of corporeal action, as it conducted Sir Isaac Newton in his grand researches.

Let us just consider how we reason in a new case. Let A and B be two magnets fastened on the ends of two long wooden laths AE, BF, which turn horizontally on pivots C, D, like compass needles, with their north poles fronting each other, twelve inches apart; and let A be pushed towards B, so that it would move uniformly with the velocity of two inches in a second. The phenomena which have been observed are as follow: A will gradually diminish its velocity; and when it has advanced about nine inches, will stop completely. B in the mean time will gradually acquire motion; and when it has advanced about nine inches, will have a velocity of about two inches per second, with which it will continue to move uniformly. Now, what is inferred from these phenomena? Because the motion of A is gradually retarded, we infer that a retarding force, that is, a force in the direction BA, has acted on it. And since this would not have happened if B had not been there, and always happens when B is there, we infer that B is either its cause or the occasion of its action. The vulgar say that B repels A; and so also say the dynamists. The abettors of invisible fluids say that a stream of fluid issuing from B impels A in the opposite direction. All naturalists agree in saying, that an active force connected with B has destroyed the motion of A, and consider this curious phenomenon as the indication and characteristic of a discovery. The same inference is made from the motion produced in B; it is considered by all as effected by a force exerted or occasioned by the presence of A; wherefore the dynamists and the vulgar say that A repels B. And both parties conclude, from the equal changes made on both bodies, that the changing forces are equal; here acknowledging that they observe an equality of action and re-action; and they add this to the other instances of the extent of this law of motion. All this while no one thinks of the inertia or inactivity of B, but, on the contrary, conclude this to be a curious instance of its activity, and most people conclude that both bodies carry about with them a vis insita both when at rest and when in motion.

If other phenomena give unquestionable evidence that in ordinary collisions there is the same changes of motion, produced without mathematical contact, the same inferences must be drawn; and a scrupulous naturalist will doubt whether contact should make any change in our reasonings on the subject, and whether actual contact ever has been or can be observed. He will also be convinced, that whilst this is the general, or perhaps universal, process of nature in producing motion by impulse, all explanations of the action of bodies e distanti, by the intervention of ethers and other invisible fluids, are nothing but multiplying the difficulties; for instead of one fact, the approach of one magnet, for instance, to another, they substitute millions of unseen impulses, each of which equally needs an explanation. And if this fluid be supposed to produce its effects by any peculiarity in its constitution, as in the case of Newton's elastic ether, proposed by him to explain gravitation, the hypothesis substitutes, in the most unqualified manner, millions of similar phenomena for the one to be explained; for there is the same want of a second fluid in order to produce that mutual recess of the particles of the ether which constitutes its elasticity.

And this seems to be the limit to our inquiries into all the classes of natural phenomena. We find the masses of the particles of matter ended, in fact, with qualities which affect the state of other particles or masses, at smaller or at greater distances from each other, according to certain general rules or laws. This ultimate step in the constitution of things is inscrutable by us. It is arrogance in the highest degree for us to say, that because we do not comprehend how there is inherent in a body any quality by which another body may be affected at any distance from it, therefore no such quality is possible. It is no less so to say, that matter has no active property but that of moving other matter by impulse; and that because it may be so moved, and also by the agency of our own minds, therefore, when it is not moved by impulse, it is moved by minds. The same almighty fiat which brought a particle of matter into existence could bring those qualities equally into existence; and the how in both is equally beyond our comprehension.

But, on the other hand, we must carefully guard against the incurious resting on this consideration, as a stop to further inquiry. There may be species of matter possessed of the mechanical powers, and which notwithstanding is not cognisable by our senses. All the properties of matter are not known to a person who is both deaf and blind; and beings possessed of more senses may perceive matter where we do not; and many phenomena may really be produced by the action of intervening matter, which we, from indolence or from haste, ascribe to the agency of inherent forces. The industry of philosophers has already discovered intermedia in some cases. It is now certain that air is the conductor of sound, and it is almost certain that there is such a thing as light. Let us therefore indulge conjectures of this kind, and examine the conjectures by the received laws of motion, and reject them when we find the smallest inconsistency; and always keep in mind, that even the most coincident with the phenomena is still but a possibility.

We may conclude the whole of these observations with the remark, that the questions about the activity or inactivity of matter are not physical, but metaphysical. Natural philosophy, it is true, commonly takes it for granted that matter is wholly inactive; but it is not of any moment in physics whether this opinion be true or false. Whether matter be acted on according to certain laws, or whether it act of itself according to the same laws, makes no difference to the natural philosopher. It is his business to discover the laws which really obtain, and to apply these to the solution of subordinate phenomena; but whether these laws arise from the nature of some agent external to matter, or whether matter itself is the agent, are questions which may be above his comprehension, and do not immediately concern his proper business. The account we have now given of natural philosophy points out to us in the plainest manner the way in which the study must be prosecuted, and the helps which must be taken from other branches of human knowledge. The causes, powers, forces, or by whatever name we choose to express them, which produce the mechanical phenomena of the universe, are not observed, and are known to us only in the phenomena themselves. Our knowledge of the mechanical powers of nature must therefore keep pace with our knowledge of the motions, and indeed is nothing different from it. In order to discover and determine the forces by which the moon is retained in her orbit round the earth, we must know her motions. To a terrestrial spectator she appears to describe an ellipse, having the earth in one focus; but, in the mean time, the earth is carried round the sun, and the moon's real path, in absolute space, is a much more complicated figure. Till we know this figure, and the variations in the velocity with which it is described, we know nothing of the forces which actuate the moon in her orbit.

When Newton says that the forces by which she is retained in this elliptical orbit are directed to the earth, what does he mean? Only this, that the deflections from that uniform rectilineal motion which she would otherwise have performed are always in this direction. In like manner, when he says that these forces are inversely proportional to the squares of her distances from the earth, he only means that the deflections made in equal times in different parts of her motion are in this proportion. These deflections are considered as the characteristics and measures of the forces. We imagine that we have made all plain when we call this indicated cause a tendency to the earth; but we have no notion of this tendency to the earth different from the approach itself. This word tendency, so fashionable amongst the followers of Sir Isaac Newton, is perverted from its pure and original sense. Tendere versus solemnis, is, in the language of Rome, and also of Newton, to go towards the sun; but we now use the words tend, tendency, to signify, not the approach, but the cause of this approach; and when called upon to speak still plainer, we desert the safe paths of plain language, and express ourselves by metaphor, speaking of visus, conatus, vis centripeta, and the like. When these expressions have become familiar, the original sense of the word is forgotten, and we take it for granted that the words never had another meaning; and this metaphor, sprung from the poverty of language, becomes a fruitful source of misconception and mistake. The only way to secure ourselves against such mystical notions as are introduced by these means into philosophy, is to have recourse to the way in which we acquire the knowledge of these fancied powers; and then we see that their names are only names for phenomena, and that universal gravitation is only an universal mutual approach amongst the parts of the solar system.

There is one case in which we fondly imagine that we know the cause independently of the effect, and that we could have predicted the phenomenon a priori; we mean the case of impulse; and hence it is that we are so prone to reduce everything to cases of impulsion, and that we have fallen upon all those subterfuges of ethers and other subtle fluids. But we might have saved ourselves all this trouble; for after having, by much false reasoning and gratuitous assumptions, shown that the phenomenon in question might have been produced by impulse, we are no nearer our purpose, because that property by which matter in motion puts other matter in motion, is known to us only by and in the effect. The fair and logical deduction from all this is, that we must not expect any knowledge of the powers of nature, the immediate causes of the motions of bodies, but by means of a knowledge of the motions themselves; and that every mistake in the motions is accompanied by a similar mistake in the causes. It is impossible to demonstrate or explain the gravitation of the planets to him who is ignorant of the properties of the ellipse, or the theory of gunnery to him who does not know the parabola.

A notion has been sometimes advanced, that a man may become a natural philosopher without mathematical knowledge; but this is entertained by none who have any regard for mathematics themselves; and surely those who are ignorant of mathematics should not be sustained as judges in this matter. We need only appeal to fact. It is only in those parts of natural philosophy which have been mathematically treated, that the investigations have been carried on with certainty, success, and utility. Without this guide, we must expect nothing but a school-boy's knowledge, resembling that of the man who takes up his religious creed on the authority of his priest, and can neither give a reason for what he imagines that he believes, nor apply it with confidence to any valuable purpose in life. These observations, on the other hand, show us the nature of the knowledge which may be acquired, and the rank which natural philosophy holds among the sciences.

Motions are the real and only objects of our observation, the only subjects of our discussion. In motion are included ideas of no ideas but those of space and time, the subjects of pure mathematical disquisition. As soon, therefore, as we have discovered the fact, the motion, all our future reasonings about this motion are purely mathematical, depending only on the affections of figure, number, and proportion, and must carry along with them that demonstration and irresistible evidence which is the boast of the science. To this we are indebted for that accuracy which is attained, and the progress which has been made, in some branches of mechanical philosophy; for when the motions are distinctly and minutely understood, and then considered only as mathematical quantities, independently of all physical considerations, and we proceed according to the just rules of mathematical reasoning, we need not fear any intricacy of combination or multiplicity of steps; we are certain that truth will accompany us, even though we do not always attend to it, and will emerge in our final proposition, in the same manner as we see happen in a long and intricate algebraic analysis.

It appears from what has been said, that mechanical philosophy is almost wholly a mathematical study, and that it is to be successfully prosecuted only under this form; but in our endeavours to initiate the young beginner, it will often be found to require more steadiness of thought than can generally be expected for keeping the mind engaged in such abstract speculations. The object presented to the mind is not readily apprehended with that vivacity which is necessary for enabling us to reason upon it with clearness and steadiness, and it would be very desirable to have some means of rendering the conception more easy, and the attention more lively. This may be done by exhibiting to the eye an experiment, which, though but a single fact, gives us a sensible object of perception, which we can contemplate and remember with much more steadiness than any mere creature of the imagination. We could, by an accurate description, give such a conception of a room that the hearer should perfectly comprehend our narration of any occurrence in it; but one moment's glance at the room would be infinitely better. It is usual therefore to employ experiments to assist the imagination of the beginner; and most courses of natural philosophy are accompanied by a series of such experiments. Such experiments, connected by a slight train of argumentative discourse, may even serve to give a notion of the general doctrines, sufficient for an elegant amusement, and even tending to excite curiosity, and engage in a serious prosecution of the study. Such are the usual courses which go by the name of Experimental Philosophy. But this is a great misapplication of the term; such courses are Experimental Philosophy is the investigation of general laws, as yet unknown, by experiment; and this is the most infallible, and indeed the sole way of arriving at the knowledge of them. This is the Nouum Organum Scientiarum strongly recommended by Lord Bacon. It was new in his time, though not altogether without example; for it is the procedure of nature, and is followed whenever curiosity is excited. There was even extant in his time, as we have already mentioned, a very beautiful example of this method, namely, the Treatise of the Loadstone, by Dr Gilbert of Colchester; a work which has hardly been excelled by any, and which, when we consider its date, about the year 1580, is really a most wonderful performance.

The most perfect model of this method is the Optics of Sir Isaac Newton. Dr Black's Essay on Magnesia is another very perfect example; and Dr Franklin's Theory of Electricity is a third example of great merit. That the investigation is not complete, nor the conclusions certain, is not an objection. The method is without fault; and a proper direction is given to the mind for the experiments which are still necessary for establishing the general laws.

It were much to be wished that some person of talents and of extensive knowledge would give a treatise on the method of inquiry by experiment. Although many beautiful and successful examples have been given as particular branches of inquiry, we have but too many instances of very inaccurate and inconclusive investigations. Experiments made at random, almost without a view, serve but little to advance our knowledge. They are like shapeless lumps of stone merely detached from the rock, but still wanting the skill of the builder to select them for the different purposes which they may chance to serve; whilst well-contrived experiments are blocks cut out by a skilful workman, according as the quarry could furnish them, and of forms suited to certain determined uses in the future edifice. Every little series of experiments by Margraef terminates in a general law, whilst hardly any general conclusion can be drawn from the numberless experiments of Pott. Lord Bacon has written much on this subject, and with great judgment and acuteness of distinction; but he has exceeded in this, and has fatigued his readers by his numerous rules; and there is in all his philosophical works, and particularly in this, a quaintness and affectation which greatly obscure his meaning, so that this most valuable part of his writings is very little read.

A formidable objection has been made to this method of inquiry. Since a physical law is only the expression of a general fact, and is established only in consequence of our having observed a similarity in a great number of particular facts; and since the great rule of inductive logic is to give the law no greater extent than the induction on which it is founded; how comes it that a few experiments must be received as the foundation of a general inference? This has been answered in very general terms in the article Philosophy. But it will be of use to consider the subject a little more particularly. Our observations on this subject are taken from the dissertation on evidence by Dr Campbell in his Philosophy of Rhetoric.

An attentive consideration of the objects around us will inform us that they are generally of a complicated nature, not only as consisting of a complication of those qualities of things called accidents, such as gravity, mobility, colour, figure, solidity, which are common to all bodies; but also as consisting of a mixture of a variety of substances, very different in their nature and properties; and each of these is perhaps compounded of ingredients more simple. Moreover, the farther we advance in the knowledge of nature, we find the more reason to be convinced of her constancy in all her operations. Like causes have always produced like effects, and like effects have always been preceded by like causes. Inconstancy sometimes appears in nature's works at first sight; but a more refined experience shows us that this is but an appearance, and that there is no inconstancy; and we explain it to our satisfaction in this way.

Most of the objects being of a complicated nature, we find, upon an accurate scrutiny, that the effects ascribed to them ought often to be solely ascribed to one or more of these component parts, whilst the others either do not contribute to them, or hinder their production; and the variety of nature is so great, that hardly any two individuals of the same species are in every respect like any other. On all these accounts we expect dissimilitudes in the phenomena accompanying perfectly similar treatment of different subjects of the same kind; but we find, that whenever we can be assured that the two substances are perfectly alike, the phenomena arising from similar treatment are the same; and long and extensive observation teaches us, that there are certain circumstances which insure us in the perfect similarity of constitution of some things. Whenever we observe the effect of any natural agent on one, but one, of these, we invariably expect that the same will be produced on any other.

Should a botanist meet with a plant new to him, and observe that it has seven monopetalous flowers, he will conclude with the utmost confidence that every plant of this species will have monopetalous flowers; but he will not suppose that it will have seven, and no more than seven, flowers. Now these two facts seem to have no difference to warrant such a difference in the conclusion; which may therefore seem capricious, since there is but one example of both. But it is not from this example only that he draws the conclusion. Had he never before taken notice of any plant, he would not have reasoned at all from these remarks. But his mind runs immediately from this unknown species to all the known species of this genus, and to all the genera of the same order; and having experienced in the figure of the flower an uniformity in every species, genus, and order, which admits of no exception, but, in the number of flowers, a variety as boundless as are the circumstances of soil, climate, age, and culture, he learns to mark the difference, and draws the above-mentioned conclusions. Thus we learn, that perfect uniformity is not to be expected in any instance whatever, because in no instance is the simplicity of constitution sufficiently great to give us assurance of perfect uniformity in the circumstances of the case; and the utmost that our experience can teach us is a quick discrimination of those circumstances which produce the occasional varieties.

The nearer that our investigations carry us to the knowledge of elementary natures, the more are we convinced by general experience of the uniformity of the operations of real elements; and although it may perhaps be impossible for us ever to arrive at the knowledge of the simplest elements of any body, yet when anything appears simple, or rather so exactly uniform, as that we have invariably observed it to produce similar effects, on discovering any new effect of this substance, we conclude, from a general experience of the efficient, a little constancy in the energy as to the rest. Fire consumes wood, melts lead, and hardens clay. In these instances it acts uniformly, but not in these only. We have always found, that whatever of any species is consumed by it in one instance, has been consumed by it upon trial at any time. If therefore a trial be made for the first time of its influence on any particular substance, he who makes it is warranted to conclude that the effect, whatever it may be, is a faithful representative of its effects on this substance in all past and future ages. This conclusion is not founded on this single instance, but upon this instance combined with the general experience of the regularity of this element in its operations.

This general conclusion, therefore, drawn from one experiment, is by no means in opposition to the great rule of inductive logic, but, on the contrary, it is the most general and refined application of it. General laws are here the real subject of consideration; and a law still more general, that nature is constant in all its operations, is the inference which is here applied as a principle of explanation of a phenomenon which is itself a general law, viz. that nature is constant in this operation.

The foundation of this general inference from one experiment being so firmly established, it is evident that experiments must be an infallible method of attaining to the knowledge of nature; and we need only be solicitous that we proceed in a way agreeable to the great rule of inductive logic; that is, the subject must be cleared of every accidental and unknown circumstance, and put into a situation that will reduce the interesting circumstance to a state of the greatest possible simplicity. Thus we may be certain that the event will be a faithful representative of every similar case; and unless this be done in the preparation, nothing can result from the most numerous experiments but uncertainty and mistakes.

The account which has been given of mechanical philosophy would seem to indicate that experiment was not of much use in the farther prosecution of it. The two laws of motion, with the assistance of mathematics, seem fully adequate to the explanation of every phenomenon; and so they are to a certain degree. But this degree is as yet very limited. Our mathematical knowledge, great as it is in comparison with that of former times, is still insufficient for giving accurate solutions even of questions, comparatively speaking, very simple. We can tell, with the utmost precision, what will be the motions of two particles of matter, or two bodies, which act on each other with forces proportioned to the squares of the distances inversely; but if we add a third particle, or a third body, acting by the same law, the united science of all Europe can only give an approximation to the solution.

What is to be done, then, in the cases which come continually before us, where millions of particles are acting at once upon each other in every variety of situation and distance? How shall we determine, for instance, the motion of water through a pipe or sluice when urged by a piston or by its own weight? what will be its velocity and direction? It is impossible, in the present state of mathematical knowledge, to tell with any precision or certainty. And here we must have recourse to experiment. But if this be the case, must the experiment be made in every possible variety of situation, depth, figure, pressure? or is it possible to find out any general rules, founded on the general laws of motion, and rationally deduced from them? Or, if this cannot be accomplished, will experiment itself furnish any general coincidences which show such mutual dependences, that we may consider them as indications of general principles, though subordinate, complicated, and perhaps inscrutable? This can be discovered by experiment alone.

The attention of philosophers has been directed to each of these three chances, and very considerable progress has been made in them all. Numerous experiments have been made, and are almost sufficient to direct the practice in many important cases, without the help of any rule or principle whatever. But there are many cases, and these of by far the greatest importance, such as the motion of a ship impelled by the winds, resisted by the water, and tossed by the waves, where distinct experiments cannot be made.

Newton, Bernoulli, D'Alembert, and others, have laboured hard to deduce from the laws of motion rules for determining what may be called the average motion of water in these circumstances, without attempting to define the path or motion of any individual particle; and they have actually deduced many rules which have a great degree of probability. It may here be asked, Why do you try to say probability? The rules, as far as they go, should be certain. So they are; they are strict deductions from their premises. But the premises are only suppositions, of various degrees of probability, assumed in order to simplify the circumstances of the case, and to give room for mathematical reasoning; therefore these deductions, these rules, must be examined by experiment. Some of the suppositions are such as can hardly be refused, and the rules deduced from them are found to tally precisely with the phenomena. Such is this, that the velocities of issuing water in similar circumstances are in the sub-duplicate ratio of the pressures. And this rule gives most important and extensive information to the engineer. Other suppositions are more gratuitous, and the rules deduced from them are less coincident with the phenomena. The patient and sagacious Newton has repeatedly failed in his attempts to determine what is the absolute velocity of water issuing from a hole in the bottom of the vessel when urged by its weight alone, and the attempts of the others have hardly succeeded better. Experiment is therefore absolutely necessary on this head.

Those who have aimed at the discovery of rules purely experimental on this subject, have also been pretty successful; and the Chevalier de Buat has, from a comparison of an immense variety of experiments made by himself and various others, deduced an empirical rule, which will not be found to deviate from truth above one part in ten in any case which has yet come to our knowledge.

This instance may serve to show the use of experiments in mechanical philosophy. It is highly proper in all cases by way of illustration; and it is absolutely necessary in most, either as the foundation of a characteristic of a particular class of phenomena, or as argument in support of a particular doctrine. Hydrostatics, hydraulics, pneumatics, magnetism, electricity, and optics, can hardly be studied in any other way.

Having in the preceding paragraphs given a pretty full enumeration of the different subjects which are to be considered in the study of natural philosophy, it will not be found necessary to spend much time in a detail of the advantages which may reasonably be expected from a successful prosecution of this study. It stands in no need of panegyric; its intimate connection with the arts gives it a sufficient recommendation to the attention of every person. It is the foundation of many arts, and it gives liberal assistance to all. Indebted to them for its origin and birth, it has ever retained its filial attachment, and repaid all their favours with the most partial affection.

To this science the navigator must have recourse for that astronomical knowledge which enables him to find his place in the trackless ocean; and although very small scraps of this knowledge are sufficient for the mere pilot, it is necessary that the study be prosecuted to the utmost by some persons, that the unlearned pilot may get that scanty pittance which must direct his routine. The few pages of tables of the sun's declination, which he uses every day to find his latitude, required the successive and united labours of all the astronomers of Europe to make them tolerably exact; and in order to ascertain his longitude with precision, it required all the genius of a Newton to detect the lunar irregularities, and to bring them within the power of the calculator; and, until this was done, the respective position of the different parts of the earth could not be ascertained. Vain would have been the attempt to do this by geodetical surveys, indepen- dently of astronomical observation. It is only from the most refined mechanics that we can hope for sure principles to direct us in the construction and management of a ship, the boast of human art, and the great means of union and communication between the different quarters of the globe.

A knowledge of mechanics not much inferior to this is necessary for enabling the architect to execute some of his greatest works, such as the erection of domes and arches, which depend on the nicest adjustment of equilibrium. Without this he cannot unite economy with strength, and his works must either be clumsy masses or flimsy shells. The effects of artillery cannot be understood or secured without the same knowledge. The whole employment of the engineer, civil or military, is a continual application of almost every branch of mechanical knowledge; and whilst the promises of a Smeaton, a Watt, a Belidor, may be confided in as if already performed, the numberless failures and disappointments in the most important and costly projects show us daily the ignorance of the pretending crowd of engineers.

The microscope, the steam-engine, the thunder-rod, are presents which the world has received from the natural philosopher; and although the compass and the telescope were the productions of chance, they would have been of little service had they not been studied and improved by Gilbert, Halley, and Dollond.

But it is not in the arts alone that the influence of natural philosophy is perceived; it lends its aid to every science, and in every study. It is often necessary to have recourse to the philosopher in disputes concerning property; and many examples might be given where great injustice has been the consequence of the ignorance of the judges. Knowledge of nature might have prevented many disgraceful condemnations for sorcery. The historian who is ignorant of natural philosophy easily admits the miraculous into his narrations, accompanies these with his reflections, draws consequences from them, and fills his pages with prodigies, fables, and absurdity.

It is almost needless to speak of the advantages which will accrue to the physician from this study. So close is the connection between it and medicine, that our language has given but one name to the naturalist and to the medical philosopher. Indeed the whole of his study is a close observation of the laws of material nature, in order to draw from them precepts to direct his practice in the noble art of healing. During the immaturity of general knowledge, whilst natural philosophy was the only study which had acquired any just pretension to certainty either in its principles or method of investigation, the physicians endeavoured to bring the objects of their study within its province, hoping by this means to get a more distinct view of it; and they endeavoured to explain the abstruse phenomena of the animal functions by reducing them all to motions, vibrations, collisions, impulses, hydrostatic and hydraulic pressures and actions, with which the mechanical philosophers were so ardently occupied at that time. But unfortunately their acquaintance with nature was then very limited, and they were but little habituated to the rules of just reasoning; and their attempts to explain the economy of animal life by the laws of mechanics did them but little service either for the knowledge of diseases or for that of the methods of cure. The mechanical theories of medicine, which had considerable reputation about the end of the seventeenth century, were many of them very ingenious, and had an imposing appearance of symmetry and connection; but they are now forgotten, having all been formed on the narrow supposition that matter was subject only to mechanical laws.

The discovery of error, however, diminishes the chance of again going wrong, especially when the cause of error has been discovered, and the means pointed out of detecting the mistakes; and the vital principle must combine its influence with, or operate upon, the properties of rude matter. It appears therefore evident that a knowledge of the mechanical laws of the material world is not only a convenient, but a necessary accomplishment to the physician. We are fully justified in this opinion, by observing medical authors of the present day introducing into medicine theories borrowed from mechanical philosophy, which they do not understand, and which they continually misapply. Appearance of reasoning frequently conceals the errors in principle, and seldom fails to mislead.

But there is no class of men to whom this science is of more service than to those who hold the honourable office of the teachers of religion. Their knowledge in their own science, and their public utility, are prodigiously hurt by ignorance of the general frame and constitution of nature; and it is much to be lamented that this science is so generally neglected by them, or considered only as an elegant accomplishment. Nay, it is too frequently shunned as a dangerous attainment, as likely to unhinge their own faith, and taint the minds of their hearers. We hope, however, that few are either so feebly rooted in the belief of the great doctrines of religion as to fear this, or of minds so base and corrupted as to adopt and inculcate a belief which they have any suspicion of being ill founded. But many have a sort of horror at all attempts to account for the events of nature by the intervention of general causes, and think this procedure derogatory to the Divine nature, and inconsistent with the doctrine of his particular providence; believing that "a sparrow does not fall to the ground without the knowledge of our heavenly Father." Their limited conceptions cannot perceive, that, in forming the general law, the Great Artist did at one glance see it in its remotest and most minute consequence, and adjust the vast assemblage so as completely to answer every purpose of his providence. There never was a more eager inquirer into the laws of nature, or more ardent admirer of its glorious Author, than the Honourable Robert Boyle. This gentleman says, that he will always think more highly of the skill and power of that artist who should construct a machine, which, being once set a-going, would of itself continue its motion for ages, and from its inherent principles continue to answer all the purposes for which it was first contrived, than of him whose machine required the continual aid of the hand which first constructed it. It is owing to great inattention that this aversion to the operation of secondary causes has any influence on our minds. What do we mean by the introduction of secondary causes? How, in fact, do we infer the agency of any cause whatever? Would we ever have supposed any cause of the operations of nature, had they gone on without any order or regularity? Or would such a chaos of events, any more than a chaos of existences, have given us any notion of a forming and directing hand? No, surely. We see the hand of God in the regular and unvaried course of nature, only because it is regular and unvaried. The philosopher expresses this by saying that the phenomena proceed by unalterable laws. Greatly mistaken therefore are they who think that we supersede the existence of mind and of providence when we trace things to their causes. A physical law being an unvaried fact, is an indication, and the strongest possible indication, of an unerring mind, who is incapable of change, and must do to-day what he always did; for to change is to deviate from what is best.1 The operations of unerring mind will therefore be regular and invariable.

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1 Ferguson's Lectures on Ethics. Physical laws, therefore, or secondary causes, are the best proofs of unerring wisdom. Such regularity of conduct is universally considered as an indication of wisdom amongst men. The wise man is known by the constancy of his conduct, whilst nobody can depend upon the future conduct of a fool.

And what astonishing evidences of wisdom do we not observe in the general laws of the material world? They will ever be considered by the intelligent philosopher as the most glorious display of inconceivable wisdom, which has been able, by means so few and so simple, to produce effects which by their grandeur astonish our feeble understandings, and by their inexhaustible variety elude all possibility of enumeration. Whilst the teachers of religion remain ignorant of the beautiful laws of nature, the great characteristics of the wisdom and goodness of the Almighty Creator, their hearers are deprived of much sublime pleasure; God is robbed of that praise which he would have received from an enlightened people; and the only worship he receives is tainted with mean notions of his attributes, and groundless fears of his power.

But besides these advantages which accrue to different classes of men from this study, there are some effects which are general, and are too important to be passed over unnoticed. That spirit of dispassionate experimental inquiry which has so greatly promoted this study, will carry with it, into every subject of inquiry, that precision and that constant appeal to fact and experience which characterize it. And we may venture to assert, that the superior good order and method which distinguish some of the later productions in other sciences, have been in a great measure owing to this mathematical spirit, the success of which in natural philosophy has gained it credit, and thus given it an unperceived influence even over those who have not made it their study.

The truths also which the naturalist discovers are such as do not in general affect the passions of men, and have therefore a good chance of meeting with a candid reception. Those whose interest it is to keep men in political or in religious ignorance cannot easily suspect bad consequences from improvements in this science; and, if they did, have hardly any pretext for checking its progress. Besides, discoveries accustom the mind to novelty; and it will vantages of no longer be startled by any consequences, however contrary to common opinion. Thus the way is paved for a rational and discreet scepticism, and a free inquiry on other subjects. Experiment, not authority, will be considered as the test of truth; and under the guidance of fair experience we need fear no ill as long as the laws of nature remain as they are.

Lastly, since it is the business of philosophy to describe the phenomena of nature, to discover their causes, to trace the connection and subordination of these causes, and thus to obtain a view of the whole constitution of nature, it is plain that it affords the surest path for arriving at the knowledge of the great cause of all, of God himself, and for forming proper conceptions of him and of our relations to him; notions infinitely more just than can ever be entertained by the careless spectator of his works. Things which to this man appear solitary and detached, having no other connection with the rest of the universe but the shadowy and fleeting relation of co-existence, will, to the diligent philosopher, declare themselves to be parts of a great and harmonious whole, connected by the general laws of nature, and all tending to one grand and beneficent purpose. Such a contemplation is in the highest degree pleasant and cheering, and cannot fail to impress us with the wish of co-operating in this glorious plan, by acting worthy of the place we hold amongst the works of God, and with the hopes of one day enjoying all the satisfaction which can arise from conscious worth and consummate knowledge; and this is the worship which God will approve. "This universe," says Boyle, "is the magnificent temple of its great Author; and man is ordained, by his powers and qualifications, the high priest of nature, to celebrate divine service in this temple of the universe." (B.B.)