The direct observations by which Demokritus showed the existence of a vacuum were — 1. A vessel with ashes in it will hold as much water as if it were empty: hence we know that there are pores in the ashes, into which the water is received. 2. Wine can be compressed in skins. 3. The growth of organised bodies proves that they have pores, through which new matter in the form of nourishment is admitted. (Aristot. Physic. iv. 6, p. 213, b.)
Besides this, Demokritus set forth motion as an indisputable fact, ascertained by the evidence of sense: and affirmed that motion was impossible, except on the assumption that vacuum existed. Melissus, the disciple of Parmenides, inverted the reasoning, in arguing against the reality of motion. If it be real (he said), then there must exist a vacuum: but no vacuum does or can exist: therefore there is no real motion. (Aristot. Physic. iv. 6.)
Since Demokritus started from these facts of sense, as the base of his hypothesis of atoms and vacua, so Aristotle (Gen. et Corr. i. 2; De Animâ, i. 2) might reasonably say that he took sensible appearances as truth. But we find Demokritus also describing reason as an improvement and enlightenment of sense, and complaining how little of truth was discoverable by man. See Mullach, Demokritus (pp. 414, 415). Compare Philippson — Ὗλη ἀνθρωπίνη — Berlin, 1831.
[204] Aristotel. Gen. et Corr. i. 8, p. 325, a. 25, τὰ πρῶτα μεγέθη τὰ ἀδιαίρετα στερεά. Diogen. Laert. ix. 44; Plutarch, adv. Koloten, p. 1110 seq.
Zeller, Philos. der Griech., vol. i. p. 583-588, ed. 2nd; Aristotel. Metaphys. Z. 13, p. 1039, a. 10, ἀδύνατον εἶναί φησι Δημόκριτος ἐκ δύο ἓν ᾒ ἐξ ἑνὸς δύο γενέσθαι· τὰ γὰρ μεγέθη τὰ ἄτομα τὰς οὐσίας ποιεῖ.
Primordial atoms differed only in magnitude, figure, position, and arrangement — they had no qualities, but their movements and combinations generated qualities.
The bridge, broken down by Parmenides, between the real and the phenomenal world, was thus in theory re-established. For the real world, as described by Demokritus, differed entirely from the sameness and barrenness of the Parmenidean Ens, and presented sufficient movement and variety to supply a basis of explanatory hypothesis, accommodated to more or less of the varieties in the phenomenal world. In respect of quality, indeed, all the atoms were alike, not less than all the vacua: such likeness was (according to Demokritus) the condition of their being able to act upon each other, or to combine as phenomenal aggregates.[205] But in respect to quantity or magnitude as well as in respect to figure, they differed very greatly: moreover, besides all these diversities, the ordination and position of each atom with regard to the rest were variable in every way. As all objects of sense were atomic compounds, so, from such fundamental differences — partly in the constituent atoms themselves, partly in the manner of their arrangement when thrown into combination — arose all the diverse qualities and manifestations of the compounds. When atoms passed into new combination, then there was generation of a new substance: when they passed out of an old combination there was destruction: when the atoms remained the same, but were merely arranged anew in order and relative position, then the phenomenon was simply change. Hence all qualities and manifestations of such compounds were not original, but derivative: they had no “nature of their own,” or law peculiar to them, but followed from the atomic composition of the body to which they belonged. They were not real and absolute, like the magnitude and figure of the constituent atoms, but phenomenal and relative — i.e. they were powers of acting upon correlative organs of sentient beings, and nullities in the absence of such organs.[206] Such were the colour, sonorousness, taste, smell, heat, cold, &c., of the bodies around us: they were relative, implying correlative percipients. Moreover they were not merely relative, but perpetually fluctuating; since the compounds were frequently changing either in arrangement or in diversity of atoms, and every such atomic change, even to a small extent, caused it to work differently upon our organs.[207]
[205] Aristotel. Gener. et Corr. i. 7, p. 323, b. 12. It was the opinion of Demokritus, that there could be no action except where agent and patient were alike. Φησὶ γὰρ τὸ αὐτὸ καὶ ὅμοιον εἶναι τό τε ποιοῦν καὶ τὸ πάσχον· οὐ γὰρ ἐγχωρεῖν τὰ ἕτερα καὶ διαφέροντα πάσχειν ὑπ’ ἀλλήλων· ἀλλὰ κἂν ἕτερα ὄντα ποιῇ τι εἰς ἄλληλα, οὐχ ᾗ ἕτερα, ἀλλ’ ᾗ ταὐτόν τι ὑπάρχει, ταύτῃ τοῦτο συμβαίνειν αὐτοῖς. Many contemporary philosophers affirmed distinctly the opposite. Τὸ ὅμοιον ὑπὸ τοῦ ὁμοίου πᾶν ἀπαθές, &c. Diogenes the Apolloniate agreed on this point generally with Demokritus; see above, p. 61, [note 1]. The facility with which these philosophers laid down general maxims is constantly observable.
[206] Aristot. Gen. et Corr. i. 2, p. 316, a. 1; Theophrast. De Sensu, s. 63, 64. Περὶ μὲν οὖν βαρέος καὶ κούφου καὶ σκληροῦ καὶ μαλακοῦ ἐν τούτοις ἀφορίζει· τῶν δὲ ἄλλων αἰσθητῶν οὐδενὸς εἶναι φύσιν, ἀλλὰ πάντα πάθη τῆς αἰσθήσεως ἀλλοιουμένης, ἐξ ἧς γίνεσθαι τὴν φαντασίαν, &c.
Stobæus, Eclog. Physic. i. c. 16. Φύσιν μὲν μηδὲν εἶναι χρῶμα, τὰ μὲν γὰρ στοιχεῖα ἄποια, τά τε μεστὰ καὶ τὸ κενόν· τὰ δ’ ἐξ αὐτῶν συγκρίματα κέχρῶσθαι διαταγῇ τε καὶ ῥυθμῷ καὶ προτροπῇ, &c.