sun, too, and moon, and stars, are seen by them such as
they really are, and their felicity in other respects is correspondent
with these things.

"And such, indeed, is the nature of the whole earth and the parts about
the earth; but there are many places all round it throughout its
cavities, some deeper and more open than that in which we dwell: but
others that are deeper have less chasm than in our region, and other are
shallower in depth than they are here, and broader.

"But all these are in many places perforated one into another under the
earth, some with narrower and some with wider channels, and have
passages through, by which a great quantity of water flows from one into
another, as into basins, and there are immense bulks of ever-flowing
rivers under the earth, both of hot and cold water, and a great quantity
of fire, and mighty rivers of fire, and many of liquid mire, some purer
and some more miry, as in Sicily there are rivers of mud that flow
before the lava, and the lava itself, and from these the several places
are filled, according as the overflow from time to time happens to come
to each of them. But all these move up and down as it were by a certain
oscillation existing in the earth. And this oscillation proceeds from
such natural cause as this: one of the chasms of the earth is
exceedingly large, and perforated through the entire earth, and is that
which Homer[43] speaks of, 'very far off, where is the most profound
abyss beneath the earth,' which elsewhere both he and many other poets
have called Tartarus. For into this chasm all rivers flow together, and
from it flow out again, but they severally derive their character from
the earth through which they flow."

[Footnote 43: _Iliad_, lib. viii., v. 14.]

"And the reason why all streams flow out from thence and flow into it is
because this liquid has neither bottom nor base. Therefore it oscillates
and fluctuates up and down, and the air and the wind around it do the
same; for they accompany it, both when it rushes to those parts of the
earth, and when to these. And as in respiration the flowing breath is
continually breathed out and drawn in, so there the wind, oscillating
with the liquid, causes certain vehement and irresistible winds both as
it enters and goes out. When, therefore, the water rushing in descends
to the place which we call the lower region, it flows through the earth
into the streams there and fills them, just as men pump up water