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

Among the researches of Demokritus there were some relating to animal generation, and zoology; but we cannot find that his opinions on these subjects were in peculiar connection with his atomic theory.219 Nor do we know how far he carried out that theory into detail by tracing the various phenomenal manifestations to their basis in atomic reality, and by showing what particular magnitude, figure, and arrangement of atoms belonged to each. It was only in some special cases that he thus connected determinate atoms with compounds of determinate quality; for example, in regard to the four Empedoklean elements. The atoms constituting heat or fire he affirmed to be small and globular, the most mobile, rapid, and penetrating of all; those constituting air, water, and earth, were an assemblage of all varieties of figures, but differed from each other in magnitude — the atoms of air being apparently smallest, those of earth largest.220

In regard to mind or soul generally, he identified it with heat or fire, conceiving it to consist in the same very small, globular, rapidly movable atoms, penetrating everywhere: which he illustrated by comparison with the fine dust seen in sunbeams when shining through a doorway. That these were the constituent atoms of mind, he proved by the fact, that its first and most essential property was to move the body, and to be itself moved.221 Mind, soul, the vital principle, fire, heat, &c., were, in the opinion of Demokritus, substantially identical — not confined to man or even to animals, but diffused, in unequal proportions, throughout plants, the air, and nature generally. Sensation, thought, knowledge, were all motions of mind or of these restless mental particles, which Demokritus supposed to be distributed over every part of the living body, mingling and alternating with the corporeal particles.222 It was the essential condition of life, that the mental particles should be maintained in proper number and distribution throughout the body; but by their subtle nature they were constantly tending to escape, being squeezed or thrust out at all apertures by the pressure of air on all the external parts. Such tendency was counteracted by the process of respiration, whereby mental or vital particles, being abundantly distributed throughout the air, were inhaled along with air, and formed an inward current which either prevented the escape, or compensated the loss, of those which were tending outwards.

Though Demokritus conceived those mental particles as distributed all over the body, yet he recognised different mental aptitudes attached to different parts of the body. Besides the special organs of sense, he considered intelligence as attached to the brain, passion to the heart, and appetite to the liver:224 the same tripartite division afterwards adopted by Plato. He gave an explanation of perception or sensation in its different varieties, as well as of intelligence or thought. Sensation and thought were, in his opinion, alike material, and alike mental. Both were affections of the same peculiar particles, vital or mental, within us: both were changes operated in these particles by effluvia or images from without; nevertheless the one change was different from the other.225

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

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.

Farther, Demokritus conceived that the diversities of taste were generated by corresponding diversities of atoms, or compounds of atoms, of particular figure, magnitude and position. Acid taste was caused by atoms rough, angular, twisted, small, and subtle, which forced their way through all the body, produced large interior vacant spaces, and thereby generated great heat: for heat was always proportional to the amount of vacuum within.233 Sweet taste was produced by spherical atoms of considerable bulk, which slid gently along and diffused themselves equably over the body, modifying and softening the atoms of an opposite character. Astringent taste was caused by large atoms with many angles, which got into the vessels, obstructing the movement of fluids both in the veins and intestines. Salt taste was produced by large atoms, much entangled with each other, and irregular. In like manner Demokritus assigned to other tastes particular varieties of generating atoms: adding, however, that in every actual substance, atoms of different figures were intermingled, so that the effect of each on the whole was only realised in the ratio of the preponderating figure.234 Lastly, the working of all atoms, in the way of taste, was greatly modified by the particular system upon which they were brought to act: effects totally opposite being sometimes produced by like atoms upon different individuals.235