[107] _De Rer. Nat._ v. 564, 650, 680, 727. Seneca, however, had, on the whole, a more advanced appreciation of the relations of the earth to the heavenly bodies. He believed the sun to be larger than our globe, and that a thousand stars might be put together without equalling his mass (284, 288). He thought the heavens to be so vast as to afford space for the swiftest of the planets to rush along with uninterrupted speed during full thirty years (7). He showed his enlightened outlook upon astronomical possibilities when he surmised that comets may have orbits that carry them far beyond the Zodiac, and when he conjectured that other planets than those then known remained to be discovered (296–299). And yet, sharing these more enlarged conceptions, he clung with curious pertinacity to some of the old childish faith which was natural in the infancy of mankind. He knew that some philosophers held that it is the earth which revolves and not the heavens, and though he does not deliberately reject this opinion, it is evident that he still held that the heavens circle round the earth.[108] Again and again he expresses his conviction that the force which sustains the energy of the sun and the stars consists of the exhalations that arise from the surface of the earth. These exhalations, he says, are the pasturage of the heavenly bodies, the breath of the world. It would be impossible, he asserts, for the earth to furnish so ample a store of nourishment to bodies larger than itself unless it were full of breath which is passing off from every part of its surface both by day and night. To the obvious objection that the supply of this energy would soon become exhausted, he has the reply that this exhaustion would certainly take place were it not that the elements are in a condition of continual transformation, issuing in one form, passing into each other, and returning to their original positions, thence to begin their cycle anew (55, 198, 244–5). In this universal transmutation water passes into air, air into water; air likewise is changed into fire, fire into air, while earth is formed from water, and water from earth (120). [108] See _postea_, Notes on Book VII. In his general conception of the universe, Seneca, as a Stoic philosopher, recognised a principle of evolution. He believed that the world embraces in its constitution everything that it is destined to experience from its beginning to its end. As a human embryo contains the germ of the future man, so at the first creation of the universe, sun and moon, the changes of the stars, and the birth of living things were all embraced. And there were likewise included the forces whereby the earth is affected, and which will ultimately lead to the final destruction of the globe (151).[109] [109] Lucretius, too, had his views on evolution, which are well expressed in four lines of verse: