Then, you think that under the moon there runs light air, quite inadequate to support a solid mass, while the earth, in Pindar’s[312] words, is compassed “by pillars set on adamant”. And this is why Pharnaces has no fear on his own account of the earth’s falling, but pities those who lie under the orbit of the moon, Ethiopians, say, or Taprobanes, on whom so great a weight might fall! Yet the moon has that which helps her against falling, in her very speed and the swing of her passage round, as objects placed in slings are hindered from falling by the [Sidenote: D] whirl of the rotation. For everything is borne on in its own natural direction unless this is changed by some other force. Therefore the moon is not drawn down by her weight, since that tendency is counteracted by her circular movement. Perhaps it would be more reasonable to wonder if she were entirely at rest as the earth is, and unmoved. As things are, the moon has a powerful cause to prevent her from being borne down upon us; but the earth, being destitute of any other movement, might naturally be moved[313] by its own weight; being heavier than the moon not merely in proportion to its greater bulk, [Sidenote: E] but because the moon has been rendered lighter by heat and conflagration. It would actually seem that the moon, if she is a fire, is in need of earth, a solid substance whereon she moves and to which she clings, so feeding and keeping up the force of her flame. For it is impossible to conceive fire as maintained without fuel. But you Stoics say that our earth stands firm without foundation or root.’ ‘Of course,’ said Pharnaces, ‘it keeps its proper and natural place, namely the essential middle point, that place around which all weights press and [Sidenote: F] bear, converging towards it from all sides. But all the upper region, even if it receive any earth-like body thrown up with force, immediately thrusts it out hitherward, or rather lets it go, to be borne down by its own momentum.’ VII. At this point, wishing Lucius to have time to refresh his memory, I called on Theon: ‘Theon, which of the tragic poets has said that physicians _Purge bitter bile with bitter remedies?_’