7. We can scarcely do better, in fine, than follow Plato.
In the universe as a whole there must necessarily be such a degree of solidity, that is to say, of resistance, as will ensure that the earth, set in the centre, be a sure footing and support to the living beings moving over it, and inevitably communicate something of its own density to them: the earth will possess coherence by its own unaided quality, but visibility by the presence of fire: it will contain water against the dryness which would prevent the cohesion of its particles; it will hold air to lighten its bulky matters; it will be in contact with the celestial fire- not as being a member of the sidereal system but by the simple fact that the fire there and our earth both belong to the ordered universe so that something of the earth is taken up by the fire as something of the fire by the earth and something of everything by everything else.
This borrowing, however, does not mean that the one thing taking-up from the other enters into a composition, becoming an element in a total of both: it is simply a consequence of the kosmic fellowship; the participant retains its own being and takes over not the thing itself but some property of the thing, not air but air's yielding softness, not fire but fire's incandescence: mixing is another process, a complete surrender with a resultant compound not, as in this case, earth- remaining earth, the solidity and density we know- with something of fire's qualities superadded.
We have authority for this where we read:
"At the second circuit from the earth, God kindled a light": he is speaking of the sun which, elsewhere, he calls the all-glowing and, again, the all-gleaming: thus he prevents us imagining it to be anything else but fire, though of a peculiar kind; in other words it is light, which he distinguishes from flame as being only modestly warm: this light is a corporeal substance but from it there shines forth that other "light" which, though it carries the same name, we pronounce incorporeal, given forth from the first as its flower and radiance, the veritable "incandescent body." Plato's word earthy is commonly taken in too depreciatory a sense: he is thinking of earth as the principle of solidity; we are apt to ignore his distinctions and think of the concrete clay.
Fire of this order, giving forth this purest light, belongs to the upper realm, and there its seat is fixed by nature; but we must not, on that account, suppose the flame of earth to be associated with the beings of that higher sphere.
No: the flame of this world, once it has attained a certain height, is extinguished by the currents of air opposed to it. Moreover, as it carries an earthy element on its upward path, it is weighed downwards and cannot reach those loftier regions. It comes to a stand somewhere below the moon- making the air at that point subtler- and its flame, if any flame can persist, is subdued and softened, and no longer retains its first intensity, but gives out only what radiance it reflects from the light above.
And it is that loftier light- falling variously upon the stars; to each in a certain proportion- that gives them their characteristic differences, as well in magnitude as in colour; just such light constitutes also the still higher heavenly bodies which, however, like clear air, are invisible because of the subtle texture and unresisting transparency of their material substance and also by their very distance.