1It must be observed, that the whole of this Essay was written previous to the date here mentioned; and that the return of the comet happened agreeably to the prediction.
1It must be observed, that the whole of this Essay was written previous to the date here mentioned; and that the return of the comet happened agreeably to the prediction.
But of all the attempts of the Newtonian philosophy, that which would appear to be the most above the reach of human reason and experience, is the attempt to compute the weights and densities of the Sun, and of the several Planets. An attempt, however, which was indispensably necessary to complete the coherence of the Newtonian system. The power of attraction which, according to the theory of gravity, each body possesses, is in proportion to the quantity of matter contained in that body. But the periodic time in which one body, at a given distance, revolves round another that attracts it, is shorter in proportion as this power is greater, and consequently as the quantity of matter in the attracting body. If the densities of Jupiter and Saturn were the same with that of the Earth, the periodic times of their several Satellites would be shorter than by observation they are found to be. Because the quantity of matter, and consequently the attracting power of each of them, would be as the cubes of their diameters. By comparing the bulks of those Planets, and the periodic times of their Satellites, it is found that, upon the hypothesis of gravity, the density of Jupiter must be greater than that of Saturn, and the density of the Earth greater than that of Jupiter. This seems to establish it as a law in the system, that the nearer the several Planets approach to the Sun, the density of their matter is the greater: a constitution of things which seems to be the most advantageous of any that could have been established; as water of the same density with that of our Earth, would freeze under the Equator of Saturn, and boil under that of Mercury.
Such is the system of Sir Isaac Newton, a system whose parts are all more strictly connected together, than those of any other philosophical hypothesis. Allow his principle, the universality of gravity, and that it decreases as the squares of the distance increase, and all the appearances, which he joins together by it, necessarily follow. Neither is their connection merely a general and loose connection, as that of most other systems, in which either these appearances, or some such like appearances, might indifferently have been expected. It is everywhere the most precise and particular that can be imagined, and ascertains the time, the place, the quantity, the duration of each individual phenomenon, to be exactly such as, by observation, they have been determined to be. Neither are the principles of union, which it employs, such as the imagination can find any difficulty in going along with. The gravity of matter is, of all its qualities, after its inertness,384that which is most familiar to us. We never act upon it without having occasion to observe this property. The law too, by which it is supposed to diminish as it recedes from its centre, is the same which takes place in all other qualities which are propagated in rays from a centre, in light, and in every thing else of the same kind. It is such, that we not only find that it does take place in all such qualities, but we are necessarily determined to conceive that, from the nature of the thing, it must take place. The opposition which was made in France, and in some other foreign nations, to the prevalence of this system, did not arise from any difficulty which mankind naturally felt in conceiving gravity as an original and primary mover in the constitution of the universe. The Cartesian system, which had prevailed so generally before it, had accustomed mankind to conceive motion as never beginning, but in consequence of impulse, and had connected the descent of heavy bodies, near the surface of the Earth, and the other Planets, by this more general bond of union; and it was the attachment the world had conceived for this account of things, which indisposed them to that of Sir Isaac Newton. His system, however, now prevails over all opposition, and has advanced to the acquisition of the most universal empire that was ever established in philosophy. His principles, it must be acknowledged, have a degree of firmness and solidity that we should in vain look for in any other system. The most sceptical cannot avoid feeling this. They not only connect together most perfectly all the phenomena of the Heavens, which had been observed before his time; but those also which the persevering industry and more perfect instruments of later Astronomers have made known to us have been either easily and immediately explained by the application of his principles, or have been explained in consequence of more laborious and accurate calculations from these principles, than had been instituted before. And even we, while we have been endeavouring to represent all philosophical systems as mere inventions of the imagination, to connect together the otherwise disjointed and discordant phenomena of Nature, have insensibly been drawn in, to make use of language expressing the connecting principles of this one, as if they were the real chains which Nature makes use of to bind together her several operations. Can we wonder then, that it should have gained the general and complete approbation of mankind, and that it should now be considered, not as an attempt to connect in the imagination the phenomena of the Heavens, but as the greatest discovery that ever was made by man, the discovery of an immense chain of the most important and sublime truths, all closely connected together, by one capital fact, of the reality of which we have daily experience.
* * * * * * * *
* * * * * * * *
385
Note by the Editors.
The Author, at the end of this Essay, left some Notes and Memorandums, from which it appears, that he considered this last part of his History of Astronomy as imperfect, and needing several additions. The Editors, however, chose rather to publish than suppress it. It must be viewed, not as a History or Account of Sir Isaac Newton’s Astronomy, but chiefly as an additional illustration of those Principles in the Human Mind which Mr. Smith has pointed out to be the universal motives of Philosophical Researches.
FROMarranging and methodizing the System of the Heavens, Philosophy descended to the consideration of the inferior parts of Nature, of the Earth, and of the bodies which immediately surround it. If the objects, which were here presented to its view, were inferior in greatness or beauty, and therefore less apt to attract the attention of the mind, they were more apt, when they came to be attended to, to embarrass and perplex it, by the variety of their species, and by the intricacy and seeming irregularity of the laws or orders of their succession. The species of objects in the Heavens are few in number; the Sun, the Moon, the Planets, and the Fixed Stars, are all which those philosophers could distinguish. All the changes too, which are ever observed in these bodies, evidently arise from some difference in the velocity and direction of their several motions; but the variety of meteors in the air, of clouds, rainbows, thunder, lightning, winds, rain, hail, snow, is vastly greater; and the order of their succession seems to be still more irregular and inconstant. The species of fossils, minerals, plants, animals, which are found in the Waters, and near the surface of the Earth, are still more intricately diversified; and if we regard the386different manners of their production, their mutual influence in altering, destroying, supporting one another, the orders of their succession seem to admit of an almost infinite variety. If the imagination, therefore, when it considered the appearances in the Heavens, was often perplexed, and driven out of its natural career, it would be much more exposed to the same embarrassment, when it directed its attention to the objects which the Earth presented to it, and when it endeavoured to trace their progress and successive revolutions.
To introduce order and coherence into the mind’s conception of this seeming chaos of dissimilar and disjointed appearances, it was necessary to deduce all their qualities, operations, and laws of succession, from those of some particular things, with which it was perfectly acquainted and familiar, and along which its imagination could glide smoothly and easily, and without interruption. But as we would in vain attempt to deduce the heat of a stove from that of an open chimney, unless we could show that the same fire which was exposed in the one, lay concealed in the other; so it was impossible to deduce the qualities and laws of succession, observed in the more uncommon appearances of Nature, from those of such as were more familiar, if those customary objects were not supposed, however disguised in their appearance, to enter into the composition of those rarer and more singular phenomena. To render, therefore, this lower part of the great theatre of nature a coherent spectacle to the imagination, it became necessary to suppose, first, That all the strange objects of which it consisted were made up out of a few, with which the mind was extremely familiar: and secondly, That all their qualities, operations and rules of succession, were no more than different diversifications of those to which it had long been accustomed, in these primary and elementary objects.
Of all the bodies of which these inferior parts of the universe seem to be composed, those with which we are most familiar, are the Earth, which we tread upon; the Water, which we every day use; the Air, which we constantly breathe; and the Fire, whose benign influence is not only required for preparing the common necessaries of life, but for the continual support of that vital principle which actuates both plants and animals. These therefore, were by Empedocles, and the other philosophers of the Italian school, supposed to be the elements, out of which, at least, all the inferior parts of nature were composed. The familiarity of those bodies to the mind, naturally disposed it to look for some resemblance to them in whatever else was presented to its consideration. The discovery of some such resemblance united the new object to an assortment of things, with which the imagination was perfectly acquainted. And if any analogy could be observed betwixt the operations and laws of succession of the compound, and those of the simple objects, the movement of the fancy, in tracing their progress,387became quite smooth, and natural, and easy. This natural anticipation, too, was still more confirmed by such a slight and inaccurate analysis of things, as could be expected in the infancy of science, when the curiosity of mankind, grasping at an account of all things before it had got full satisfaction with regard to any one, hurried on to build, in imagination, the immense fabric of the universe. The heat, observed in both plants and animals, seemed to demonstrate, that Fire made a part of their composition. Air was not less necessary for the subsistence of both, and seemed, too, to enter into the fabric of animals by respiration, and into that of plants by some other means. The juices which circulated through them showed how much of their texture was owing to Water. And their resolution into Earth by putrefaction discovered that this element had not been left out in their original formation. A similar analysis seemed to show the same principles in most of the other compound bodies.
The vast extent of those bodies seemed to render them, upon another account, proper to be the great stores out of which nature compounded all the other species of things. Earth and Water divide almost the whole of the terrestrial globe between them. The thin transparent covering of the Air surrounds it to an immense height upon all sides. Fire, with its attendant, light, seems to descend from the celestial regions, and might, therefore, either be supposed to be diffused through the whole of those etherial spaces, as well as to be condensed and conglobated in those luminous bodies, which sparkle across them, as by the Stoics; or, to be placed immediately under the sphere of the Moon, in the region next below them, as by the Peripatetics, who could not reconcile the devouring nature of Fire with the supposed unchangeable essence of their solid and crystalline spheres.
The qualities, too, by which we are chiefly accustomed to characterize and distinguish natural bodies, are all of them found, in the highest degree in those Four Elements. The great divisions of the objects, near the surface of the Earth, are those into hot and cold, moist and dry, light and heavy. These are the most remarkable properties of bodies; and it is upon them that many of their other most sensible qualities and powers seem to depend. Of these, heat and cold were naturally enough regarded by those first enquirers into nature, as the active, moisture and dryness, as the passive qualities of matter. It was the temperature of heat and cold which seemed to occasion the growth and dissolution of plants and animals; as appeared evident from the effects of the change of the seasons upon both. A proper degree of moisture and dryness was not less necessary for these purposes; as was evident from the different effects and productions of wet and dry seasons and soils. It was the heat and cold, however, which actuated and determined those two otherwise inert qualities of things, to a state either of rest or motion. Gravity and levity were regarded388as the two principles of motion, which directed all sublunary things to their proper place: and all those six qualities, taken together, were, upon such an inattentive view of nature, as must be expected in the beginnings of philosophy, readily enough apprehended to be capable of connecting together the most remarkable revolutions, which occur in these inferior parts of the universe. Heat and dryness were the qualities which characterized the element of Fire; heat and moisture that of Air; moisture and cold that of Water; cold and dryness that of Earth. The natural motion of two of these elements, Earth and Water, was downwards, upon account of their gravity. This tendency, however, was stronger in the one than in the other, upon account of the superior gravity of Earth. The natural motion of the two other elements, Fire and Air, was upwards, upon account of their levity; and this tendency, too, was stronger in the one than in the other, upon account of the superior levity of Fire. Let us not despise those ancient philosophers, for thus supposing, that these two elements had a positive levity, or a real tendency upwards. Let us remember, that this notion has an appearance of being confirmed by the most obvious observations; that those facts and experiments, which demonstrate the weight of the Air, and which no superior sagacity, but chance alone, presented to the moderns, were altogether unknown to them; and that, what might, in some measure, have supplied the place of those experiments, the reasonings concerning the causes of the ascent of bodies, in fluids specifically heavier than themselves, seem to have been unknown in the ancient world, till Archimedes discovered them, long after their system of physics was completed, and had acquired an established reputation: that those reasonings are far from being obvious, and that by their inventor, they seem to have been thought applicable only to the ascent of Solids in Water, and not even to that of Solids in Air, much less to that of one fluid in another. But it is this last only which could explain the ascent of flame, vapours, and fiery exhalations, without the supposition of a specific levity.
Thus, each of those Four Elements had, in the system of the Universe, a place which was peculiarly allotted to it, and to which it naturally tended. Earth and Water rolled down to the centre; the Air spread itself above them; while the Fire soared aloft, either to the celestial region, or to that which was immediately below it. When each of those simple bodies had thus obtained its proper sphere, there was nothing in the nature of any one of them to make it pass into the place of the other, to make the Fire descend into the Air, the Air into the Water, or the Water into the Earth; or, on the contrary, to bring up the Earth into the place of the Water, the Water into that of the Air, or the Air into that of the Fire. All sublunary things, therefore, if left to themselves, would have remained in an eternal repose. The revolution of the heavens, those of the Sun, Moon, and Five Planets,389by producing the vicissitudes of Day and Night, and of the Seasons, prevented this torpor and inactivity from reigning through the inferior parts of nature; inflamed by the rapidity of their circumvolutions, the element of Fire, and forced it violently downwards into the Air, into the Water, and into the Earth, and thereby produced those mixtures of the different elements which kept up the motion and circulation of the lower parts of Nature; occasioned, sometimes, the entire transmutation of one element into another, and sometimes the production of forms and species different from them all, and in which, though the qualities of them all might be found, they were so altered and attempered by the mixture, as scarce to be distinguishable.
Thus, if a small quantity of Fire was mixed with a great quantity of Air, the moisture and moderate warmth of the one entirely surmounted and changed into their own essence the intense heat and dryness of the other; and the whole aggregate became Air. The contrary of which happened, if a small quantity of Air was mixed with a great quantity of Fire: the whole, in this case, became Fire. In the same manner, if a small quantity of Fire was mixed with a great quantity of Water, then, either the moisture and cold of the Water might surmount the heat and dryness of the Fire, so that the whole should become Water; or, the moisture of the Water might surmount the dryness of the Fire, while, in its turn, the heat of the Fire surmounted the coldness of the Water, so as that the whole aggregate, its qualities being heat and moisture, should become Air, which was regarded as the more natural and easy metamorphosis of the two. In the same manner they explained how like changes were produced by the different mixtures of Fire and Earth, Earth and Water, Water and Air, Air and Earth; and thus they connected together the successive transmutations of the elements into one another.
Every mixture of the Elements, however, did not produce an entire transmutation. They were sometimes so blended together, that the qualities of the one, not being able to destroy, served only to attemper those of the other. Thus Fire, when mixed with Water, produced sometimes a watery vapour, whose qualities were heat and moisture; which partook at once of the levity of the Fire, and of the gravity of the Water, and which was elevated by the first into the Air, but retained by the last from ascending into the region of Fire. The relative cold, which they supposed prevailed in the middle region of the Air, upon account of its equal distance, both from the region of Fire, and from the rays that are reflected by the surface of the Earth, condensed this vapour into Water; the Fire escaped it, and flew upwards, and the Water fell down in rain, or, according to the different degrees of cold that prevailed in the different seasons, was sometimes congealed into snow, and sometimes into hail. In the same manner, Fire, when mixed with Earth, produced sometimes a fiery exhalation, whose qualities390were heat and dryness, which being elevated by the levity of the first into the Air condensed by the cold, so as to take fire, and being at the same time surrounded by watery vapours, burst forth into thunder and lightning, and other fiery meteors. Thus they connected together the different appearances in the Air, by the qualities of their Four Elements; and from them, too, in the same manner, they endeavoured to deduce all the other qualities in the other homogeneous bodies, that are near the surface of the Earth. Thus, to give an example, with regard to the hardness and softness of bodies; heat and moisture, they observed, were the great softeners of matter. Whatever was hard, therefore, owed that quality either to the absence of heat, or to the absence of moisture. Ice, crystal, lead, gold, and almost all metals, owed their hardness to the absence of heat, and were, therefore, dissolvable by Fire. Rock-salt, nitre, alum, and hard clay, owed that quality to the absence of moisture, and were therefore, dissolvable in water. And, in the same manner, they endeavoured to connect together most of the other tangible qualities of matter. Their principles of union, indeed, were often such as had no real existence, and were always vague and undetermined in the highest degree; they were such, however, as might be expected in the beginnings of science, and such as, with all their imperfections, could enable mankind both to think and to talk, with more coherence, concerning those general subjects, than without them they would have been capable of doing. Neither was their system entirely devoid either of beauty or magnificence. Each of the Four Elements having a particular region allotted to it, had a place of rest, to which it naturally tended, by its motion, either up or down, in a straight line, and where, when it had arrived, it naturally ceased to move. Earth descended, till it arrived at the place of Earth; Water, till it arrived at that of Water; and Air, till it arrived at that of Air; and there each of them tended to a state of eternal repose and inaction. The Spheres consisted of a Fifth Element, which was neither light nor heavy, and whose natural motion made it tend, neither to the centre, nor from the centre, but revolve round it in a circle. As, by this motion, they could never change their situation with regard to the centre, they had no place of repose, no place to which they naturally tended more than to any other, but revolved round and round for ever. This Fifth Element was subject neither to generation nor corruption, nor alteration of any kind; for whatever changes may happen in the Heavens, the senses can scarce perceive them, and their appearance is the same in one age as in another. The beauty, too, of their supposed crystalline spheres seemed still more to entitle them to this distinction of unchangeable immortality. It was the motion of those Spheres, which occasioned the mixtures of the Elements, and from hence, the production of all the forms and species, that diversify the world. It was the approach of the Sun and of the391other Planets, to the different parts of the Earth, which, by forcing down the element of Fire, occasioned the generation of those forms. It was the recess of those bodies, which, by allowing each Element to escape to its proper sphere, brought about, in an equal time, their corruption. It was the periods of those great lights of Heaven, which measured out to all sublunary things, the term of their duration, of their growth, and of their decay, either in one, or in a number of seasons, according as the Elements of which they were composed, were either imperfectly or accurately blended and mixed with one another. Immortality, they could bestow upon no individual form, because the principles out of which it was formed, all tending to disengage themselves, and to return to their proper spheres, necessarily, at last, brought about its dissolution. But, though all individuals were thus perishable, and constantly decaying, every species was immortal, because the subject-matter out of which they were made, and the revolution of the Heavens, the cause of their successive generations, continued to be always the same.
In the first ages of the world, the seeming incoherence of the appearances of nature, so confounded mankind, that they despaired of discovering in her operations any regular system. Their ignorance, and confusion of thought, necessarily gave birth to that pusillanimous superstition, which ascribes almost every unexpected event, to the arbitrary will of some designing, though invisible beings, who produced it for some private and particular purpose. The idea of an universal mind, of a God of all, who originally formed the whole, and who governs the whole by general laws, directed to the conservation and prosperity of the whole, without regard to that of any private individual, was a notion to which they were utterly strangers. Their gods, though they were apprehended to interpose, upon some particular occasions, were so far from being regarded as the creators of the world, that their origin was apprehended to be posterior to that of the world. The Earth, according to Hesiod, was the first production of the chaos. The Heavens arose out of the Earth, and from both together, all the gods, who afterwards inhabited them. Nor was this notion confined to the vulgar, and to those poets who seem to have recorded the vulgar theology. Of all the philosophers of the Ionian school, Anaxagoras, it is well known, was the first who supposed that mind and understanding were requisite to account for the first origin of the world, and who, therefore, compared with the other philosophers of his time, talked, as Aristotle observes, like a sober man among drunkards; but whose opinion was, at the time, so remarkable, that he seems to have got a sirname from it. The same notion, of the spontaneous origin of the world, was embraced, too, as the same author tells, by the early Pythagoreans, a sect, which, in the ancient world, was never regarded as irreligious. Mind, and understanding, and consequently Deity, being392the most perfect, were necessarily, according to them, the last productions of Nature. For in all other things, what was most perfect, they observed, always came last. As in plants and animals, it is not the seed that is most perfect, but the complete animal, with all its members, in the one; and the complete plant, with all its branches, leaves, flowers, and fruits, in the other. This notion, which could take place only while Nature was still considered as, in some measure, disorderly and inconsistent in her operations, was necessarily renounced by those philosophers, when, upon a more attentive survey, they discovered, or imagined they had discovered, more distinctly, the chain which bound all her different parts to one another. As soon as the Universe was regarded as a complete machine, as a coherent system, governed by general laws, and directed to general ends, viz. its own preservation and prosperity, and that of all the species that are in it; the resemblance which it evidently bore to those machines which are produced by human art, necessarily impressed those sages with a belief, that in the original formation of the world there must have been employed an art resembling the human art, but as much superior to it, as the world is superior to the machines which that art produces. The unity of the system, which, according to this ancient philosophy, is most perfect, suggested the idea of the unity of that principle, by whose art it was formed; and thus, as ignorance begot superstition, science gave birth to the first theism that arose among those nations, who were not enlightened by divine Revelation. According to Timæus, who was followed by Plato, that intelligent Being who formed the world endowed it with a principle of life and understanding, which extends from its centre to its remotest circumference, which is conscious of all its changes, and which governs and directs all its motions to the great end of its formation. This soul of the world was itself a God, the greatest of all the inferior, and created deities; of an essence that was indissoluble, by any power but by that of him who made it, and which was united to the body of the world, so as to be inseparable by every force, but his who joined them, from the exertion of which his goodness secured them. The beauty of the celestial spheres attracting the admiration of mankind, the constancy and regularity of their motions seeming to manifest peculiar wisdom and understanding, they were each of them supposed to be animated by an Intelligence of a nature that was, in the same manner, indissoluble and immortal, and inseparably united to that sphere which it inhabited. All the mortal and changeable beings which people the surface of the earth were formed by those inferior deities; for the revolutions of the heavenly bodies seemed plainly to influence the generation and growth of both plants and animals, whose frail and fading forms bore the too evident marks of the weakness of those inferior causes, which joined their different parts to one another. According to Plato and Timæus, neither the393Universe, nor even those inferior deities who govern the Universe, were eternal, but were formed in time, by the great Author of all things, out of that matter which had existed from all eternity. This at least their words seemed to import, and thus they are understood by Cicero, and by all the other writers of earlier antiquity, though some of the later Platonists have interpreted them differently.
According to Aristotle, who seems to have followed the doctrine of Ocellus, the world was eternal; the eternal effect of an eternal cause. He found it difficult, it would seem, to conceive what could hinder the First Cause from exerting his divine energy from all eternity. At whatever time he began to exert it, he must have been at rest during all the infinite ages of that eternity which had passed before it. To what obstruction, from within or from without, could this be owing? or how could this obstruction, if it ever had subsisted, have ever been removed? His idea of the nature and manner of existence of this First Cause, as it is expressed in the last book of his Physics, and the five last chapters of his Metaphysics, is indeed obscure and unintelligible in the highest degree, and has perplexed his commentators more than any other parts of his writings. Thus far, however, he seems to express himself plainly enough: that the First Heavens, that of the Fixed Stars, from which are derived the motions of all the rest, is revolved by an eternal, immovable, unchangeable, unextended being, whose essence consists in intelligence, as that of a body consists in solidity and extension; and which is therefore necessarily and always intelligent, as a body is necessarily and always extended: that this Being was the first and supreme mover of the Universe: that the inferior Planetary Spheres derived each of them its peculiar revolution from an inferior being of the same kind; eternal, immovable, unextended, and necessarily intelligent: that the sole object of the intelligences of those beings was their own essence, and the revolution of their own spheres; all other inferior things being unworthy of their consideration; and that therefore whatever was below the Moon was abandoned by the gods to the direction of Nature, and Chance, and Necessity. For though those celestial beings were, by the revolutions of their several Spheres, the original causes of the generation and corruption of all sublunary forms, they were causes who neither knew nor intended the effects which they produced. This renowned philosopher seems, in his theological notions, to have been directed by prejudices which, though extremely natural, are not very philosophical. The revolutions of the Heavens, by their grandeur and constancy, excited his admiration, and seemed, upon that account, to be effects not unworthy a Divine Intelligence. Whereas the meanness of many things, the disorder and confusion of all things below, exciting no such agreeable emotion, seemed to have no marks of being directed by that Supreme Understanding. Yet, though this opinion saps the foundations of human worship, and must have the394same effects upon society as Atheism itself, one may easily trace, in the Metaphysics upon which it is grounded, the origin of many of the notions, or rather of many of the expressions, in the scholastic theology, to which no notions can be annexed.
The Stoics, the most religious of all the ancient sects of philosophers, seem in this, as in most other things, to have altered and refined upon the doctrine of Plato. The order, harmony, and coherence which this philosophy bestowed upon the Universal System, struck them with awe and veneration. As, in the rude ages of the world, whatever particular part of Nature excited the admiration of mankind, was apprehended to be animated by some particular divinity; so the whole of Nature having, by their reasonings, become equally the object of admiration, was equally apprehended to be animated by a Universal Deity, to be itself a Divinity, an Animal; a term which to our ears seems by no means synonymous with the foregoing; whose body was the solid and sensible parts of Nature, and whose soul was that etherial Fire, which penetrated and actuated the whole. For of all the four elements, out of which all things were composed, Fire or Ether seemed to be that which bore the greatest resemblance to the Vital Principle which informs both plants and animals, and therefore most likely to be the Vital Principle which animated the Universe. This infinite and unbounded Ether, which extended itself from the centre beyond the remotest circumference of Nature, and was endowed with the most consummate reason and intelligence, or rather was itself the very essence of reason and intelligence, had originally formed the world, and had communicated a portion, or ray, of its own essence to whatever was endowed with life and sensation, which, upon the dissolution of those forms, either immediately or some time after, was again absorbed into that ocean of Deity from whence it had originally been detached. In this system the Sun, the Moon, the Planets, and the Fixed Stars, were each of them also inferior divinities, animated by a detached portion of that etherial essence which was the soul of the world. In the system of Plato, the Intelligence which animated the world was different from that which originally formed it. Neither were these which animated the celestial spheres, nor those which informed inferior terrestrial animals, regarded as portions of this plastic soul of the world. Upon the dissolution of animals, therefore, their souls were not absorbed in the soul of the world, but had a separate and eternal existence, which gave birth to the notion of the transmigration of souls. Neither did it seem unnatural, that, as the same matter which had composed one animal body might be employed to compose another, that the same intelligence which had animated one such being should again animate another. But in the system of the Stoics, the intelligence which originally formed, and that which animated the world, were one and the same, all inferior intelligences were detached portions395of the great one; and therefore, in a longer, or in a shorter time, were all of them, even the gods themselves, who animated the celestial bodies, to be at last resolved into the infinite essence of this almighty Jupiter, who, at a distant period, should, by an universal conflagration, wrap up all things, in that etherial and fiery nature, out of which they had originally been deduced, again to bring forth a new Heaven and a new Earth, new animals, new men, new deities; all of which would again, at a fated time, be swallowed up in a like conflagration, again to be re-produced, and again to be re-destroyed, and so on without end.
INevery transmutation, either of one element into another, or of one compound body either into the elements out of which it was composed, or into another compound body, it seemed evident, that both in the old and in the new species, there was something that was the same, and something that was different. When Fire was changed into Air, or Water into Earth, the Stuff, or Subject-matter of this Air and this Earth, was evidently the same with that of the former Fire or Water; but the Nature or Species of those new bodies was entirely different. When, in the same manner, a number of fresh, green, and odoriferous flowers were thrown together in a heap, they, in a short time, entirely changed their nature, became putrid and loathsome, and dissolved into a confused mass of ordure, which bore no resemblance, either in sensible qualities or in its effects, to their former beautiful appearance. But how different soever the species, the subject-matter of the flowers, and of the ordure, was, in this case too, evidently the same. In every body therefore, whether simple or mixed, there were evidently two principles, whose combination constituted the whole nature of that particular body. The first was the Stuff, or Subject-matter, out of which it was made; the second was the Species, the Specific Essence, the Essential, or, as the schoolmen have called it, the Substantial Form of the Body.396The first seemed to be the same in all bodies, and to have neither qualities nor powers of any kind, but to be altogether inert and imperceptible by any of the senses, till it was qualified and rendered sensible by its union with some species or essential form. All the qualities and powers of bodies seemed to depend upon their species or essential forms. It was not the stuff or matter of Fire, or Air, or Earth, or Water, which enabled those elements to produce their several effects, but that essential form which was peculiar to each of them. For it seemed evident that Fire must produce the effects of Fire, by that which rendered it Fire; Air, by that which rendered it Air; and that in the same manner all other simple and mixed bodies must produce their several effects, by that which constituted them such or such bodies; that is, by their Specific Essence or essential forms. But it is from the effects of bodies upon one another, that all the changes and revolutions in the material world arise. Since these, therefore, depend upon the specific essences of those bodies, it must be the business of philosophy, that science which endeavours to connect together all the different changes that occur in the world, to determine wherein the Specific Essence of each object consists, in order to foresee what changes or revolutions may be expected from it. But the Specific Essence of each individual object is not that which is peculiar to it as an individual, but that which is common to it, with all other objects of the same kind. Thus the Specific Essence of the Water, which now stands before me, does not consist in its being heated by the Fire, or cooled by the Air, in such a particular degree; in its being contained in a vessel of such a form, or of such dimensions. These are all accidental circumstances, which are altogether extraneous to its general nature, and upon which none of its effects as Water depend. Philosophy, therefore, in considering the general nature of Water, takes no notice of those particularities which are peculiar to this water, but confines itself to those things which are common to all Water. If, in the progress of its inquiries, it should descend to consider the nature of Water that is modified by such particular accidents, it still would not confine its consideration to this water contained in this vessel, and thus heated at this fire, but would extend its views to Water in general contained in such kind of vessels, and heated to such a degree at such a fire. In every case, therefore, Species, or Universals, and not Individuals, are the objects of Philosophy. Because whatever effects are produced by individuals, whatever changes can flow from them, must all proceed from some universal nature that is contained in them. As it was the business of Physics, or Natural Philosophy, to determine wherein consisted the Nature and Essence of every particular Species of things, in order to connect together all the different events that occur in the material world; so there were two other sciences, which, though they had originally arisen out of that system of Natural Philosophy I have just397been describing, were, however, apprehended to go before it, in the order in which the knowledge of Nature ought to be communicated. The first of these, Metaphysics, considered the general nature of Universals, and the different sorts or species into which they might be divided. The second of these, Logics, was built upon this doctrine of Metaphysics; and from the general nature of Universals, and of the sorts into which they were divided, endeavoured to ascertain the general rules by which we might distribute all particular objects into general classes, and determine to what class each individual object belonged; for in this, they justly enough apprehended, consisted the whole art of philosophical reasoning. As the first of these two sciences, Metaphysics, is altogether subordinate to the second, Logic, they seem, before the time of Aristotle, to have been regarded as one, and to have made up between them that ancient Dialectic of which we hear so much, and of which we understand so little: neither does this separation seem to have been much attended to, either by his own followers, the ancient Peripatetics, or by any other of the old sects of philosophers. The later schoolmen, indeed, have distinguished between Ontology and Logic; but their Ontology contains but a small part of what is the subject of the metaphysical books of Aristotle, the greater part of which, the doctrines of Universals, and everything that is preparatory to the arts of defining and dividing, has, since the days of Porphery, been inserted into their Logic.
According to Plato and Timæus, the principles out of which the Deity formed the World, and which were themselves eternal, were three in number. The Subject-matter of things, the Species, or Specific Essences of things, and what was made out of these, the sensible objects themselves. These last had no proper or durable existence, but were in perpetual flux and succession. For as Heraclitus had said that no man ever passed the same river twice, because the water which he had passed over once was gone before he could pass over it a second time; so, in the same manner, no man ever saw, or heard, or touched the same sensible object twice. When I look at the window, for example, the visible species, which strikes my eyes this moment, though resembling, is different from that which struck my eyes the immediately preceding moment. When I ring the bell, the sound, or audible species, which I hear this moment, though resembling in the same manner, is different, however, from that which I heard the moment before. When I lay my hand on the table, the tangible species which I feel this moment, though resembling, in the same manner, is numerically different too from that which I felt the moment before. Our sensations, therefore, never properly exist or endure one moment; but, in the very instant of their generation, perish and are annihilated for ever. Nor are the causes of those sensations more permanent. No corporeal substance is ever exactly the398same, either in whole or in any assignable part, during two successive, moments, but by the perpetual addition of new parts, as well as loss of old ones, is in continual flux and succession. Things of so fleeting a nature can never be the objects of science, or of any steady or permanent judgment. While we look at them, in order to consider them, they are changed and gone, and annihilated for ever. The objects of science, and of all the steady judgments of the understanding, must be permanent, unchangeable, always existent, and liable neither to generation nor corruption, nor alteration of any kind. Such are the species or specific essences of things. Man is perpetually changing every particle of his body; and every thought of his mind is in continual flux and succession. But humanity, or human nature, is always existent, is always the same, is never generated, and is never corrupted. This, therefore, is the object of science, reason, and understanding, as man is the object of sense, and of those inconstant opinions which are founded upon sense. As the objects of sense were apprehended to have an external existence, independent of the act of sensation, so these objects of the understanding were much more supposed to have an external existence independent of the act of understanding. Those external essences were, according to Plato, the exemplars, according to which the Deity formed the world, and all the sensible objects that are in it. The Deity comprehended within his infinite essence, all these species, or external exemplars, in the same manner as he comprehended all sensible objects.
Plato, however, seems to have regarded the first of those as equally distinct with the second from what we would now call the Ideas or Thoughts of the Divine Mind,1and even to have supposed, that they had a particular place of existence, beyond the sphere of the visible399corporeal world; though this has been much controverted, both by the later Platonists, and by some very judicious modern critics, who have followed the interpretation of the later Platonists, as what did most400honour to the judgment of that renowned philosopher. All the objects in this world, continued he, are particular and individual. Here, therefore, the human mind has no opportunity of seeing any Species, or Universal Nature. Whatever ideas it has, therefore, of such beings, for it plainly has them, it must derive from the memory of what it has seen, in some former period of its existence, when it had an opportunity of visiting the place or Sphere of Universals. For some time after it is immersed in the body, during its infancy, its childhood, and a great part of its youth, the violence of those passions which it derives from the body, and which are all directed to the particular and individual objects of this world, hinder it from turning its attention to those Universal Natures, with which it had been conversant in the world from whence it came. The Ideas, of these, therefore, seem, in this first period of its existence here, to be overwhelmed in the confusion of those turbulent emotions, and to be almost entirely wiped out of its remembrance. During the continuance of this state, it is incapable of Reasoning, Science and Philosophy, which are conversant about Universals. Its whole attention is turned towards particular objects, concerning which, being directed by no general notions, it forms many vain and false opinions, and is filled with error, perplexity, and confusion. But, when age has abated the violence of its passions, and composed the confusion of its thoughts, it then becomes more capable of reflection, and of turning its attention to those almost forgotten ideas of things with which it had been conversant in the former state of its existence. All the particular objects in this sensible world, being formed after the eternal exemplars in that intellectual world, awaken, upon account of their resemblance, insensibly, and by slow degrees, the almost obliterated ideas of these last. The beauty, which is shared in different degrees among terrestrial objects, revives the same idea of that Universal Nature of beauty which exists in the intellectual world: particular acts of justice, of the universal nature of justice; particular reasonings, and particular sciences, of the universal nature of science and reasoning; particular roundnesses, of the universal nature of roundness; particular squares, of the universal nature of squareness. Thus science, which is conversant about Universals, is derived from memory; and to instruct any person concerning the general nature of any subject, is no more than to awaken in him the remembrance of what he formerly knew about it. This both Plato and Socrates imagined they could still further confirm, by the fallacious experiment,401which showed, that a person might be led to discover himself, without any information, any general truth, of which he was before ignorant, merely by being asked a number of properly arranged and connected questions concerning it.