of the stars, our vision may mislead us somewhat, “but only to a very small degree."

The sun, small as it is, may give the light and heat it does, from being, as it were, a well-head, whence light and heat gush out; or the heat may not dwell directly in itself, but it may inflame the air when in a susceptible state, as branches make a conflagration; or the sun may have about him a quantity of invisible heat, unaccompanied by fire, and this heat may increase the stroke of his rays.

Night is caused either by the sun, "when he strikes the uttermost part of heaven," having "blown out all his fires," or because "the same force which has carried his orb above the earth, compels it to pass below the earth."

Morning is caused either by the reappearance of the same sun, or 'because fires meet together, and many seeds of heat are accustomed to stream together at a fixed time, which cause new sunlight to be born every day." Strange to say, he seems to think this singular theory, if anything, more probable than the former one. He gravely says that "from the summits of Ida it is reported that scattered fires are seen to appear at daybreak, and gradually collect themselves into an orb." And if, he adds, this is really what does happen, it is only in strict analogy with many of the most familiar phenomena of nature. Trees blossom at fixed times; rain and lightning are not very irregular; and at fixed times bovs change their teeth.

In the same way, a new moon may be born every

day, figured according to its various phases. Or the moon may revolve like a spherical ball, of which one half is self-luminous and one half dark. Or it may be luminous all over, either of itself or by the light of the sun; and its phases may be caused by its carrying with it an invisible satellite that is perpetually eclipsing it. The eclipses of the sun, too, may be accounted for in the same way; or "the sun may be able, quite exhausted, to lose his fires at certain fixed times.”

Such in broad outline is the Lucretian universe-the outcome of atoms that have in themselves no sensible qualities. Let us see now, more in detail, how Lucretius accounts for all the variety of substances into which we find they have combined themselves.

This variety, and the results of it, are due to the various shapes and sizes of the atoms, and their various ways of mixing. "There is nothing," says Lucretius, "which is apparent to sense that consists of one kind of first beginnings. There is nothing which is not formed by a mixing of seed." As an obvious instance and proof of this, we have the earth, which must contain within itself the seeds of all the things that spring out of it, such as water, fire, and vegetation. For each thing is what it is in virtue of being a combination, a mixture, a clinging together of atoms of certain various shapes, in certain various proportions. It is these various combinations of various atoms that give to things their different textures and properties ; for "since seeds differ, there must be a difference in the spaces between the passages, the connections, the weights, the blows."

This hypothesis, says Lucretius, will explain all the facts of nature, and will be verified by them. Light, for instance, passes through horn; but rain is thrown off. Why? The atoms comprising horn leave in that substance spaces of a certain size and shape. The atoms that compose light are very small, and can pass through these spaces. The atoms that compose water are larger, and cannot. Again, wines flow through a strainer, but oil will not. This is because the elements of oil are larger, or more hooked and tangled, and so cannot be so easily separated. To put the matter generally, hard substances, such as diamonds and iron, are composed mainly of atoms that have many hooks, by which, the instant they touch each other, they are held together; fluid substances, such as water, are composed mainly of atoms without hooks, which can move with more or less freedom about each other; and gaseous substances are composed entirely of atoms of a finer and smaller nature still.

The various tastes, smells, sounds, and temperatures of things are due, too, to the various shapes of the atoms that compose them. Harsh tastes come from substances made up of rough, pointed, or hooked atoms; pleasant tastes, from substances made up of smooth atoms. The atoms of honey and milk, for instance, are smooth; those of wormwood rough. The creaking of a saw is made of rough atoms; beautiful music of small atoms; and so on.

More light will be thrown on this conception of things, when we come to see farther what is Lucretius's theory of sensation, and how he reduces all our percep

tions to modes of touch. In the foregoing analysis of matter, the inconsistencies and incompleteness are of course obvious. It will be enough, in passing, to mention the two most striking of these. One is, that though it is one of his great points that the atoms are far below the reach of sense, he seems continually to speak of them as though they could individually by their shape affect, or be detected, by the senses. The other is, that this application of the atomic theory quite fails to explain one of the chief phenomena of nature that is, the change of qualities that takes place in a single substance, hot things becoming cold, sweet things rancid, and gaseous and fluid things solid. This, however, by the way. What we have now to do is to examine the theory of Lucretius, not to criticise it.

SECTION III.

THE INTERACTION OF MATERIAL SUBSTANCES.

We have thus far seen how the universe as it is, was evolved out of its original elements, and the few simple laws of which this evolution was the result. We have next to consider the more complex question of how it is maintained in its present state, with all its various movements and innumerable changes, and the constant uniform relation of its larger parts.

We have seen how atoms behaved in forming sub

stances; we must now see why substances behave as they do when formed. Lucretius explains this by a doctrine we have already mentioned, that nothing, however much appearances may say the contrary to us, is really at rest. We are to conceive of everything in constant motion-solids, fluids, and gases,-in motion within themselves, even when they are at rest relatively to other objects. It is in this way that the heavens are sustained above us from falling on the earth, and the earth sustained from falling on the heavens below; for the entire space between the two is pervaded by air in ceaseless motion, the particles of which are perpetually bounding and rebounding, striking against the earth on the one hand and the heavens on the other, and thus keeping the whole in place.

It might, Lucretius seems to think, appear doubtful how, according to his theory of the downward tendency of everything, air could sustain the earth. He therefore takes pains to emphasise especially the power that is in air, fine though its atoms be. Life, which, as we shall see soon, he considers to be atomic, can hold the body together, he says; and the living body does not feel the weight of its separate members. Our feet, for instance, are conscious of no pressure from above. In the same way air prevents the earth from having any weight with reference to the universe.

But we must not only conceive of all bodies as having within themselves this perpetual motion of their particles; we must also conceive all substances as being, as it were, in a perpetual state of evaporation. Minute particles of themselves are for ever streaming off their