I say that the Starry Heaven may be compared to Physics because of three properties, and to Metaphysics because of three others.  For it shows us of itself two visible things, such as the multitude of stars and such as the Galaxy, that white circle which the common people call the Path of St. James.  It shows to us also one of the poles, and keeps the other hidden from us.  And it shows to us one movement alone from East to West; and another, which it makes from West to East, it keeps almost, as it were, hidden from us.  Therefore, in due order are to be seen, first the comparison with the Physical and then that with the Metaphysical.

I say that the Starry Heaven shows us many stars; for, according to what the wise men of Egypt have seen, even to the last star which appeared to them in the Meridian, they place there twenty-two thousand bodies of stars, of which I speak.  And in this it has the greatest similitude with Physics, if these three numbers, namely, Two, and Twenty, and Thousand, are regarded well and subtly.  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.  And I believe that they were moved by the fable of Phaeton, which Ovid relates in the beginning of the second part of his Metamorphoses.  Others said, such as Anaxagoras and Democritus, that it was the light of the Sun reflected into that part.  And these opinions, with demonstrative reasons, they proved over and over again.  What Aristotle may have said of this is not so easy to learn, because his opinion is not found to be the same in one translation as in the other; and I believe that it might be due to the error of the translators, for in the new one he seems to say that the Galaxy is a collection of vapours under the stars of that part which always attract them; and this does not seem to be the true reason.  In the old translation