7. Plato's view[217] is to be accepted. The universe must contain
something solid, impenetrable, so that the earth, when established in
the middle of the universe, might offer a firm foundation for all the
animals that walk on it, and that these animals might possess a certain
solidity by the very fact of their terrestriality; so that the earth
might, by itself, possess the property of continuousness; that it might
be illuminated by fire, might also participate in water, so as not to
be desiccated, and so that its parts might unite, and that the air
might somewhat lighten its mass.