​Note 1, p. 19. Hence Democritus, &c.] None of the works of this eminent man have come down to us; but notices of his opinions lie scattered through the writings of Aristotle, and these may suffice for the elucidation of this and other allusions to him. Following his master Leucippus, Democritus^[1], abandoning metaphysical subtleties, looked into the constitution of the external world for ​the knowledge of natural causes; and he was thus led to adopt the hypothesis of indivisible and moving corpuscles, in order to account for the universal law of motion. "Several other philosophers^[2] had, before their time, considered matter as divisible into indefinitely small particles, but as they were the first who taught that these particles were originally destitute of all qualities except figure and motion, they may well be regarded as the founders of the atomic system of philosophy." Democritus^[3] maintained that nothing can ever be produced from nothing, and that "indivisible atoms (elementary corpuscles, that is) constitute the essence of bodies." He adopted, as elements, the plenum and vacuum, making the former, in contradistinction to the latter, to be entity, and the two to be, as matter, the causes of things; he maintained too, that they are equally distributed through all bodies. He agreed with Anaxagoras in believing that throughout all nature there is a principle of combination; and with his master Leucippus, in regarding form arrangement and position of particles, as causes of elementary distinctions among bodies. But in some of this reasoning he was mistaken, Aristotle observes, from not distinguishing the condition of potentiality from reality, since the same object may simultaneously, when in potentiality, be and not be, although this cannot hold good of the same when in reality. Democritus also thought that, owing to the difference of sensation ​produced by the same object upon the same individual, truth either has no existence, or else it can hardly ever be attained to by mortal beings. To return, however, to the doctrine of atoms, Leucippus and Democritus maintained that, as bodies are distinguished by forms, and forms are infinite, elementary bodies must be infinite also; but then, with the exception of fire, which was said to be spherical, they forgot to specify what the forms are; and they denned elementary bodies by greatness and smallness as well as form. Thus, form motion and size are, according to them, the constituents of these formative atoms, and, accordingly, the larger atoms which are said to go to the formation of bodies, are distinguished from the smaller ones or motes (held to be visible only in the sun-beams), which, as being endowed with vital properties, are alluded to, in a succeeding passage, as supporting, through respiration, the life of the animal. In fine, this doctrine of atoms varying in form and size, constantly moving, and, through attraction and repulsion, combining with and separating from one another, prevailed in all the schools of antiquity; and there may perhaps be traced in it a faint outline of the present matured theory of atomic proportion.

Note 2, p. 19. Hence, too, they make breathing, &c.] This description conveys, under a rude exterior, so to say, a description of the process of breathing or respiration, as well as the purposes which it has to fulfil in the animal economy—"the contraction of the chest (expiration) ​expels particles rendered effete, and these are supplied by others from without, during inspiration; and this alternation continues so long as life endures." It emanates from an early stage of physiology, no doubt, but yet it does clearly intimate that without such an alternation life could not be maintained—that a renewing power from without, and an expulsion of something prejudicial from within, are necessary to animal existence. Democritus (of Abdera), Anaxagoras and Diogenes are cited by Aristotle^[4] as believing respiration to be necessary for all creatures (in opposition to himself, who limited the process to air-breathing animals), and he has given their account of the process in fishes and oysters (molluscs). " Anaxagoras says that fishes, during respiration, discharge the water through the branchiæ, and that then, as there may not be a vacuum, they draw in air which is in the mouth; and Diogenes maintains that, when fishes discharge the water through the branchiæ, they draw in, by means of the void created in the mouth, the air which is ever present in water and encircling the mouth." Democritus advanced a step nearer to modern teaching, in accounting for fishes dying when out of the water by their then taking in too much air; as, when in the water, they can take in only a moderate quantity." But all this was objected to, absolutely, by Aristotle, both because of his own more restricted views of respiration, and of the apparent discrepance of the theories with common sense, and thus was he led, in ​this instance, to oppose theories pregnant with suggestion, and advantageous to the progress of science.

Note 3, p. 20. To the same point do they also come, &c.] The writers here alluded to are said by Philoponus to be Plato, Xenophanes and Alcmæon. Aristotle^[5] observes that, as nature is the origin of motion and change, it is necessary, in order to comprehend motion, to understand what nature is. Motion seems to be the property only of continuity, and the infinite is displayed, first of all, in what is continuous; and, therefore, in definitions of continuity, there is frequent reference to the infinite, as if all continuity were infinitely divisible. Besides these reasons, without place void and time, there cannot be motion. But whatever is in motion, must have been moved by its own or by some other power, and this motor may be the second or third of a series, as the staff, for instance, which moves the stone is moved itself by the hand, which is moved by the man; and although the last of these may be spoken of as the motor, yet the term is applicable rather to the man, as being the first link in the chain. Thus, the man who communicates motion by his will is, himself at rest; and, therefore, it by no means follows, Aristotle contends, that the motor should itself be in motion.

Note 4, p. 21. Homer has well represented, &c.] The term ἀλλοφρονέων, rendered "changing his mind," occurs but once in the Iliad, and there it refers, not to Hector, but to Euryalus vanquished in the funeral games; and ​signifies stupefaction of the faculties rather than what is here attributed to it. Thus, either Democritus must have misquoted, or the Iliad, since Aristotle's time, have suffered, as is commonly believed, more than one mutilation. The purport of the passage, however, is sufficiently obvious.

Note 5, p. 21. Thus Democritus does not employ the term mind, &c.] He made mind, that is, to be a sentient principle and identified with those filings and emotions, which Aristotle held, as has been shewn, to be but emanations from the corporeal organs and functions, to be manifestations, that is, of the temperament. An apology has been offered for this attribution of mind to all creatures, in that such a principle may seem to be represented by the consummate order which prevails in their constitution; and thus that Anaxagoras may have meant that, while it may be present, objectively, in all beings, it can be present, subjectively, (as mind, that is) only, in a few. Plato^[6] seems to imply something like this when adopting one essence or faculty which is eternal and unbegotten, and another which has no abiding and is perishable—the one capable, by intellect with cogitation, of comprehending unchangeable natures; and the latter capable, by opinion with sensual perceptions, of comprehending whatever is casual and ephemeral.

Note 6, p. 21. Have said that the Vital Principle comprises all first causes, &c] Aristotle^[7] observes that, as ​every investigation is for the purpose of knowing something, and as we cannot be said to know before we can comprehend wherefore a thing is what it is, (comprehend, that is, its first cause,) so it is evident that we must thus study the laws of reproduction destruction and change, throughout nature, in order to be enabled to refer, for each subject of investigation, to the first causes of the phænomena. This argument seems to confine causation to natural operations in particular, that is, living bodies; but cause had then, as it has now, a far wider signification—besides essence, individual being, elements, and other admitted first causes, that of which anything is made, was said to be its cause, as bronze of a statue, silver of a goblet, and, in a general sense the maker is the cause of the production, and he who alters, of the change, &c. Thus, there was great latitude in the enumeration of first causes. Thales^[8], the founder of this branch of philosophy, maintains that water is a first cause, because the earth rose from water. Anaximenes and Democritus contend that, as air was before water, so it is rather to be regarded as the first cause of everything.

Hippasus and Heraclitus set it down as being fire; and Empedocles, adding earth, adopted four elementary causes; for he maintained, that these elements are unchangeable and unproduceable, although capable of combining with and separating from one another. He first ​adopted the four elements, in fact, as the first causes of all things, although, as he makes fire to be the antagonism of the other three, which he held to be of one nature, he can hardly be said to have regarded them as more than two. This doctrine of elements prevailed, in fact, down to the time of Descartes^[9], who admitted, however, only of three, fire, air, and earth; and he maintained that all the forms of inanimate bodies may be accounted for by the motion form size and arrangement of particles, without the aid of any agent, such as heat or cold, moisture or dryness. Thus all elementary particles are, according to him, first causes.

Note 7, p. 21. By earth we perceive, &c.] The doctrine of elements prevailed even to the constitution of the sentient organs, for, as sensibility could have no part in the theory of that age, philosophers had adopted the dogma, that like recognises and perceives by like, that air, that is, perceives by air, water by water, and so for the other elements; and thus the organ of vision was supposed to be of water, that of hearing to be of air, and that of smell to be of fire. As illustration of which, Aristotle^[10] describes "odour as being a vaporous exhalation, and, as such, necessarily derived from fire (heat); and the special organ of smell is said, on this account, to be located about the brain, for the matter of cold (the brain) is, in potentiality, hot," and, therefore, able to perceive ​what is derived from heat. The visual organ is said to be of water, and to see objects, not as being water but, as being diaphanous, as this quality belongs to air as well as water, but then water is more protective and 'condensed than air, and, therefore, the pupil and the eye are constituted of water. These are rude theories, no doubt, and sorry substitutes for the knowledge of the brain and its system; but philosophy cannot rest upon a confession of ignorance, and this hypothesis, unsatisfactory as it may now seem, was for ages the admitted theory of sentient perception. But this theory of Empedocles, however otherwise faulty, may well be supposed, without violence to the text, to convey in the terms στοργὴ and νεῖχος, a knowledge, or perception rather, of attraction and repulsion; and an assumption of these principles may be traced in most of the systems of that time concerning elementary combinations. This must be maintained with some reserve, however, as some have given a more literal version of the terms in amor and discordia, or lis, which, as moral or sentient qualities, seem to be without any relation to elementary combinations. The latin version of the phrase is, Terram nam terra, lympha cognoscimus undam, ætheraque æthere; sane ignis dignoscitur igne; sic et amore amor, ac tristi discordia lite; and the French is, "Par la terre nous voyons la terre; l'eau par l'eau; par l'air, l'air divin; par le feu, le feu qui consume; par l'amour, l'amour; et la discorde

Note 8, p. 22. In the treatises "upon philosophy," &c.] These books are said to have been expositions of the teaching of Plato and the Pythagoreans upon ideas and the nature of the sovereign good, or philosophy, and to have been gathered by Aristotle from the oral teaching of his great preceptor. It is generally believed that they have not come down to us; but a more modern commentator seems to have been persuaded that they are still preserved in the Metaphysics, (that store-house, where lie scattered the fragments of every system of philosophy that ever had any authority,) and yet there is no passage^[11] in that work, in which Aristotle alludes directly to the topics here cited by him. If a digest of Plato's^[12] doctrine of the elements may be offered, he makes fire and earth to have been the first of created elements, because whatever is produced must be visible and tangible and corporeal, and nothing can be visible without fire, or tangible without solidity, whence the body of the universe was, in the beginning, constituted out of fire and earth; but since it is scarcely possible for two elements so to coalesce as to form bodies without the intervention of other combining elements, the Creator placed water and air between fire and earth, and made them to be in the same relation to the first elements which they are to each other and thus fire is to air as air is to water, and air is to water as water is to earth. The Pythagoreans^[13] were ​the first who devoted themselves to mathematics, and, by exclusive attention to that study, they were led, at first, to consider their principles as the principles of entities; but as numbers must be before mathematics, they were brought to perceive many resemblances to beings and conditions in numbers, rather than in fire or earth, water or air. Thus, they assumed that a particular combination of numbers is justice, that another is Vital Principle and mind, another proportion or fitness; and further, perceiving the proportions and impressions of harmonic sounds to be numbers, and other things appearing to bear a resemblance to numbers, and numbers to be the first of created entities, they assumed that the elements of numbers must be the elements of entities; and that the heavens and every kind of harmony must be numbers. But some, while they held that numbers are elements, believed odd and even to be the origin of numbers, and, therefore, elements in a stricter sense; and, as the unit is derived from odd and even, they regarded it as the origin of all numbers. Enough, however, has been said for rendering apprehensible to the general reader, the import of the terms and the tenour of the argument; and it would be idle, even were the doctrine fully known, to attempt any such disquisition as would be required for a full elucidation of this the most abstruse, perhaps, of all the topics of antiquity.

Note 9, p. 22. There are writers who have combined, &c.] Simplicius^[14] and Philoponus attribute this opinion to ​Xenocrates, whom they praise as the ablest expositor of the doctrine of ideal numbers. He maintained that Vital Principle has in it an abiding source of ideas congenial with a mobile, ever-changing nature, such as pertains to the external world, and that hence it is a number which, while unable to free itself from the nature of things, approximates to ideas; and in order to prevent faculties so ungenial from being severed, he derived from Vital Principle the faculty and origin of motion, by which, as by a link, they are to be retained together. Thus, he thought to reconcile the apparent discrepance of the co-existence of ideas and things in the same being. Plato^[15] has well criticised, in one of his writings, the varying theories of philosophers upon the number, nature and relations of elementary principles.

Note 10, p. 23. Anaxagoras seems, as we have, &c.] The writing of Anaxagoras, the Clazomenian, here alluded to, appeared, according to Aristotle^[16], after those of Empedocles, although, in age he was his senior; and Anaxagoras maintained, he says, that first causes are infinite in number. Thus, that almost all homogeneous bodies, such as water or air, can be produced or destroyed only by combination and separation; and that, admitting of no other origin or destruction than these, they must endure for ever. From all which it might be inferred, that he admitted of but one cause, and that in the form of matter. He made mind, to which he attributed ​intelligence, to be a first cause, (as Empedocles made affinity to be an element,) to be innate in and the source of motion in animals, as well as the cause, in nature, of the universe and its order.

Note 11, p. 24. Thales, too, from what, &c.] In this allusion to the influence of the magnet, Thales may have been criticising the opinions which made motion dependent upon life. He was the founder of the school which derived all things from one or more material and indestructible elements; he believed water to be the sole element, (whence he demonstrated that the earth is from water), and was probably led, Aristotle observes, to this conception, from perceiving that the nutrition of all creatures is fluid; that heat is produced from water, and that by heat animals live; and, then, that all seminal particles are naturally fluid.

Note 12, p. 24. Diogenes, together with some other writers, &c.] It is probable that this opinion was suggested to Diogenes by the respiration, which he knew to be essential to animal existence and dependent upon the air; although the process itself, and the changes effected by it, were of course then unknown. Air, however, was believed to be necessary for the maintenance of life, and so it might well be regarded as the originating cause of all things; and more especially by one who saw so far, as was shewn in a former note, into its mode of agency. It is shewn by Aristotle^[17] that he had well ​studied the vascular system; and he seems to have perceived that the brain is the seat of sensation. In fine, philosophers, generally, in adopting four causes, have been divided between fire, water, and, as with Diogenes, air; which he held to be the origin of all secondary operations.

Note 13, p. 25. Others, as Critias.] The opinion that blood differs from the other fluids and has an independent vitality, has prevailed, no doubt, in all ages; but Aristotle^[18] placed it, as well as its analogue, the ichor, which circulates in molluscs, insects, &c., among insentient and excrementitious parts, such as bone, nails, cartilage, and other like parts. It may be added, too, that the brain was so considered. "To conceive," Hunter^[19] observes, "that the blood when circulating is endowed with life, is perhaps carrying the imagination as far as it can go, but the difficulty arises from its being fluid, as the mind is not accustomed to the idea of a living fluid. But when all the circumstances of this fluid are considered, the idea that it has life within it, may not appear so difficult to comprehend, for every part is formed, as we grow, out of the blood, and if it has not life previous to this operation, it must acquire it in the act of formation." One of the great proofs of the blood's vitality is to be found in coagulation, as the blood, when circulating, is not subject to certain laws to which it is subject when removed from

Note 14, p. 26. So many writers as admit.] Heat is the antagonism to cold, for it is fixed^[20], and with a downward tendency, while heat is mobile, and has an inclination upwards; heat, again, tends to dilate bodies, while cold acts by contracting them. Thus, as heat^[21] separates, and cold consolidates, they came to be looked upon as the elements or causes of destruction, (as heat appears to be self-motive and a cause of change,) and restoration. But as heat (ζέω to boil or be hot) is derived from, or is the synonym of life or living, (ζάω contr. ζῶ, ζάειν contr. ζῆν,) so some made life, from this supposed identity, to be heat; and others, from the resemblance between cold (ψυχρὸς or ψυχὸς) and the Vital Principle, (ψυχὴ) as breathing was supposed, by all the physiologists, to be a process for cooling the blood, made it to be cold. It is hardly possible to transfer to another, and that not a cognate tongue, the full sense of a passage which depends upon etymology; but the general import of these two opinions may, perhaps, be gathered from what is here said. Thus, Cervantes^[22] makes his knight fix upon the name Rocinante, because Rocin is a horse, or nag of the ordinary character; but, as his charger is to have widespread renown, and to be distinguished from all other nags, it ought to have a sonorous and suitable appellation, and this is realised, in his own opinion, by the suffix ante, and hence, Rocinante.