So the atmosphere is a part, a most necessary one, of the world. 1 This it is that joins heaven and earth, separating highest and lowest in such a way as yet to unite them. It separates by coming in between, it unites by rendering possible communication between the two. It transmits to the higher regions what it receives from the earth; and again, it transfuses terrestrial objects with the influences of the heavenly bodies. I call it a part of the world in the same sense as animals and trees are parts. The whole class of animals and trees forms 2 part of the universe, since it has to be taken in to make up the whole, and without it the universe is not complete. A single animal or tree is a quasi-part: though it is lost, that from which it is lost is still entire. Now the atmosphere, as I have been saying, adheres both to sky and earth. In both it is inborn. Whatever is an inborn part of anything else possesses unity, for without unity nothing can be born. V The earth is at once part and material of the world. You are not, I 1 think, more likely to ask why it is a part than why the sky is a part. The one is just as essential as the other to the existence of the whole, which they go to make up, and from which [from the one no less than from the other][37] sustenance is provided for all animals and crops and stars. From the earth all the strength of every man, all 2 the energy of the world with its ceaseless demands, are supplied. Hence proceeds the force that, by day and by night, sustains in their labours so many stars, so active and so eager, and that provides their food. The universal nature derives from this source what suffices for its nourishment. The world has appropriated all that it requires throughout eternity. To adopt a tiny illustration of a great subject: eggs enclose within them as much moisture as they require for the completion of the creature that is to be hatched. [37] The words in brackets are in all probability spurious, the addition of some commentator. The whole passage is very uncertain. VI