The Vacuum of the Universe

Milisos shows from these things that the universe is immovable, for if it were moved it would be necessary, says he, that there should be a vacuum. The Pythagoreans also say that there is a vacuum and that it enters into the heaven as if the heaven respired from an infinite spirit. So many therefore and such are nearly the arguments from which some assert and others deny the existence of a vacuum. In order however to understand which of the assertions are true, it is necessary to consider what the name signifies.