For by the two is meant the local movement, which is of necessity from one point to another; and by the twenty is signified the movement of the alteration, for, since from the ten upwards one advances not except by altering this ten with the other nine and with itself; and the most beautiful alteration which it receives is its own with itself, and the first which it receives is the twenty; reasonably by this number the said movement is signified.

And by the thousand is signified the movement of increase, which in name, that is, this thousand, is the greater number, and to increase still more is not possible except by multiplying this.

And these three movements alone are observed in Physics, as it is demonstrated in the fifth chapter of his first book.
And because of the Milky Way, this Heaven has a great similitude with Metaphysics.

Wherefore, it is to be known that concerning this Galaxy the Philosophers have had different opinions.

For the followers of Pythagoras said that the Sun at some time or other went astray from his path, and, passing through other parts not suitable to his fervent heat, he burnt the place through which he passed, and there remained that appearance of the conflagration.