Explanation of different sensations and perceptions. Colours.
Proceeding upon his hypothesis of atoms and vacua as the only objective existences, he tried to show what particular modifications of atoms, in figure, size, and position, produced upon the sentient the impressions of different colours. He recognised four fundamental or simple colours — white, black, red, and green — of which all other colours were mixtures and combinations.[227] White colour (he said) was caused by smooth surfaces, which presented straight pores and a transparent structure, such as the interior surface of shells: where these smooth substances were brittle or friable, this arose from the constituent atoms being at once spherical and loosely connected together, whereby they presented the clearest passage through their pores, the least amount of shadow, and the purest white colour. From substances thus constituted, the effluvia flowed out easily, and passed through the intermediate air without becoming entangled or confused with it. Black colour was caused by rough, irregular, unequal substances, which had their pores crooked and obstructed, casting much shadow, and sending forth slowly their effluvia, which became hampered and entangled with the intervening medium of air. Red colour arose from the effluvia of spherical atoms, like those of fire, though of larger size: the connection between red colour and fire was proved by the fact that heated substances, man as well as the metals, became red. Green was produced by atoms of large size and wide vacua, not restricted to any determinate shape, but arranged in peculiar order and position. These four were given by Demokritus as the simple colours. But he recognised an infinite diversity of compound colours, arising from mixture of them in different proportions, several of which he explained — gold-colour, purple, blue, violet, leek-green, nut-brown, &c.[228]
[227] Theophrastus, De Sensu, s. 73 seq.; Aristotel. De Sensu, c. iv. p. 442, b. 10. The opinions of Demokritus on colour are illustrated at length by Prantl in his Uebersicht der Farbenlehre der Alten (p. 49 seq.), appended to his edition of the Aristotelian or Pseudo-Aristotelian treatise, Περὶ Χρωμάτων (Munich, 1849).
Demokritus seems also to have attempted to show, that the sensation of cold and shivering was produced by the irruption of jagged and acute atoms. See Plutarch, De Primo Frigido, p. 947, 948, c. 8.
[228] Theophrastus, De Sensu, s. 76-78. ἄπειρα τὰ χρώματα καὶ τοὺς χυλοὺς κατὰ τὰς μίξεις — οὐδὲν γὰρ ὅμοιον ἔσεσθαι θἄτερον θἀτέρου.
Vision caused by the outflow of effluvia or images from objects. Hearing.
Besides thus setting forth those varieties of atoms and atomic motions which produced corresponding varieties of colour, Demokritus also brought to view the intermediate stages whereby they realised the act of vision. All objects, compounds of the atoms, gave out effluvia or images resembling themselves. These effluvia stamped their impression, first upon the intervening air, next upon the eye beyond: which, being covered by a fine membrane, and consisting partly of water, partly of vacuum, was well calculated to admit the image. Such an image, the like of which any one might plainly see by looking into another person’s eye, was the immediate cause of vision.[229] The air, however, was no way necessary as an intervening medium, but rather obstructive: the image proceeding from the object would be more clearly impressed upon the eye through a vacuum: if the air did not exist, vision would be so distinct, even at the farthest distance, that an object not larger than an ant might be seen in the heavens.[230] Demokritus believed that the visual image, after having been impressed upon the eye, was distributed or multiplied over the remaining body.[231] In like manner, he believed that, in hearing, the condensed air carrying the sound entered with some violence through the ears, passed through the veins to the brain, and was from thence dispersed over the body.[232] Both sight and hearing were thus not simply acts of the organ of sense, but concurrent operations of the entire frame: over all which (as has been already stated) the mental or vital particles were assumed to be disseminated.
[229] Theophrast. De Sensu, s. 50. τὸν ἀέρα τὸν μεταξὺ τῆς ὄψεως καὶ τοῦ ὁρωμένου τυποῦσθαι, &c. Aristotel. De Sensu, c. 2, p. 438, a. 6.
Theophrastus notices this intermediate ἀποτύπωσις ἐν τῷ ἀέρι as a doctrine peculiar (ἰδίως) to Demokritus: he himself proceeds to combat it (51, 52).