Plato and the Other Companions of Sokrates, 3rd ed. Volume 1

The intelligence of men and animals, very unequal in character and degree, was imbibed by respiration, the inspired air passing by means of the veins and along the blood into all parts of the body. Of the veins Diogenes gave a description remarkable for its minuteness of detail, in an age when philosophers dwelt almost exclusively in loose general analogies.188 He conceived the principal seat of intelligence in man to be in the thoracic cavity, or in the ventricle of the heart, where a quantity of air was accumulated ready for distribution.189 The warm and dry air concentrated round the brain, and reached by veins from the organs of sense, was the centre of sensation. Taste was explained by the soft and porous nature of the tongue, and by the number of veins communicating with it. The juices of sapid bodies were sucked up by it as by a sponge: the odorous stream of air penetrated from without through the nostrils: both were thus brought into conjunction with the sympathising cerebral air. To this air also the image impressed upon the eye was transmitted, thereby causing vision:190 while pulsations and vibrations of the air without, entering through the ears and impinging upon the same centre, generated the sensation of sound.

If the veins connecting the eye with the brain were inflamed, no visual sensation could take place;191 moreover if our minds or attention were absorbed in other things, we were often altogether insensible to sensations either of sight or of sound: which proved that the central air within us was the real seat of sensation.192 Thought and intelligence, as well as sensation, was an attribute of the same central air within us, depending especially upon its purity, dryness, and heat, and impeded or deadened by moisture or cold. Both children and animals had less intelligence than men: because they had more moisture in their bodies, so that the veins were choked up, and the air could not get along them freely to all parts. Plants had no intelligence; having no apertures or ducts whereby the air could pervade their internal structure. Our sensations were pleasurable when there was much air mingled with the blood, so as to lighten the flow of it, and to carry it easily to all parts: they were painful when there was little air, and when the blood was torpid and thick.193

The structure of the Kosmos Diogenes supposed to have been effected by portions of the infinite air, taking upon them new qualities and undergoing various transformations. Some air, becoming cold, dense, and heavy, sunk down to the centre, and there remained stationary as earth and water: while the hotter, rarer, and lighter air ascended and formed the heavens, assuming through the intelligence included in it a rapid rotatory movement round the earth, and shaping itself into sun, moon, and stars, which were light and porous bodies like pumice stone. The heat of this celestial matter acted continually upon the earth and water beneath, so that the earth became comparatively drier, and the water was more and more drawn up as vapour, to serve for nourishment to the heavenly bodies. The stars also acted as breathing-holes to the Kosmos, supplying the heated celestial mass with fresh air from the infinite mass without.194 Like Anaxagoras, Diogenes conceived the figure of the earth as flat and round, like a drum; and the rotation of the heavens as lateral, with the axis perpendicular to the surface of the earth, and the north pole always at the zenith.

This he supposed to have been the original arrangement; but after a certain time, the earth tilted over spontaneously towards the south — the northern half was elevated and the southern half depressed — so that the north pole was no longer at the zenith, and the axis of rotation of the heavens became apparently oblique.195 He thought, moreover, that the existing Kosmos was only of temporary duration; that it would perish and be succeeded by future analogous systems, generated from the same common substance of the infinite and indestructible air.196 Respecting animal generation — and to some extent respecting meteorological phenomena197 — Diogenes also propounded several opinions, which are imperfectly known, but which appear to have resembled those of Anaxagoras.

Nearly contemporary with Anaxagoras and Empedokles, two other enquirers propounded a new physical theory very different from those already noticed — usually known under the name of the atomic theory. This Atomic theory, though originating with the Eleate Leukippus, obtained celebrity chiefly from his pupil Demokritus of Abdera, its expositor and improver. Demokritus (born seemingly in B.C. 460, and reported to have reached extreme old age) was nine years younger than Sokrates, thirty-three years older than Plato, and forty years younger than Anaxagoras.198 The age of Leukippus is not known, but he can hardly have been much younger than Anaxagoras.

Of Leukippus we know nothing: of Demokritus, very little — yet enough to exhibit a life, like that of Anaxagoras, consecrated to philosophical investigation, and neglectful not merely of politics, but even of inherited patrimony.199 His attention was chiefly turned towards the study of Nature, with conceptions less vague, and a more enlarged observation of facts, than any of his contemporaries had ever bestowed. He was enabled to boast that no one had surpassed him in extent of travelling over foreign lands, in intelligent research and converse with enlightened natives, or in following out the geometrical relations of lines.200 He spent several years in visiting Egypt, Asia Minor, and Persia. His writings were numerous, and on many different subjects, including ethics, as well as physics, astronomy, and anthropology. None of them have been preserved. But we read, even from critics like Dionysius of Halikarnassus and Cicero, that they were composed in an impressive and semi-poetical style, not unworthy to be mentioned in analogy with Plato; while in range and diversity of subjects they are hardly inferior to Aristotle.201

The theory of Leukippus and Demokritus (we have no means of distinguishing the two) appears to have grown out the Eleatic theory.202 Parmenides the Eleate (as I have already stated) in distinguishing Ens, the self-existent, real, or absolute, on one side — from the phenomenal and relative on the other — conceived the former in such a way that its connection with the latter was dissolved. The real and absolute, according to him, was One, extended, enduring, continuous, unchangeable, immovable: the conception of Ens included these affirmations, and at the same time excluded peremptorily Non-Ens, or the contrary of Ens. Now the plural, unextended, transient, discontinuous, changeable, and moving, implied a mixture of Ens and Non-Ens, or a partial transition from one to the other. Hence (since Non-Ens was inadmissible) such plurality, &c., could not belong to the real or absolute (ultra-phenomenal), and could only be affirmed as phenomenal or relative. In the latter sense, Parmenides did affirm it, and even tried to explain it: he explained the phenomenal facts from phenomenal assumptions, apart from and independent of the absolute. While thus breaking down the bridge between the phenomenal on one side and the absolute on the other, he nevertheless recognised each in a sphere of its own.

This bridge the atomists undertook to re-establish. They admitted that Ens could not really change — that there could be no real generation, or destruction — no transformation of qualities — no transition of many into one, or of one into many. But they denied the unity and continuity and immobility of Ens: they affirmed that it was essentially discontinuous, plural, and moving. They distinguished the extended, which Parmenides had treated as an Unum continuum, into extension with body, and extension without body: into plenum and vacuum, matter and space. They conceived themselves to have thus found positive meanings both for Ens and Non-Ens. That which Parmenides called Non-Ens or nothing, was in their judgment the vacuum; not less self-existent than that which he called Something. They established their point by showing that Ens, thus interpreted, would become reconcilable to the phenomena of sense: which latter they assumed as their basis to start from. Assuming motion as a phenomenal fact, obvious and incontestable, they asserted that it could not even appear to be a fact, without supposing vacuum as well as body to be real: and the proof that both of them were real was, that only in this manner could sense and reason be reconciled. Farther, they proved the existence of a vacuum by appeal to direct physical observation, which showed that bodies were porous, compressible, and capable of receiving into themselves new matter in the way of nutrition.

Instead of the Parmenidean Ens, one and continuous, we have a Demokritean Ens, essentially many and discontinuous: plena and vacua, spaces full and spaces empty, being infinitely intermingled.203 There existed atoms innumerable, each one in itself essentially a plenum, admitting no vacant space within it, and therefore indivisible as well as indestructible: but each severed from the rest by surrounding vacant space. The atom could undergo no change: but by means of the empty space around, it could freely move. Each atom was too small to be visible: yet all atoms were not equally small; there were fundamental differences between them in figure and magnitude: and they had no other qualities except figure and magnitude. As no atom could be divided into two, so no two atoms could merge into one. Yet though two or more atoms could not so merge together as to lose their real separate individuality, they might nevertheless come into such close approximation as to appear one, and to act on our senses as a phenomenal combination manifesting itself by new sensible properties.204