 Aristotle’s refutation of the void persuaded most commentators for the next 1500 years. There were two limited dissenters to his thesis that vacuums are impossible. The Stoics agreed that terrestrial vacuums are impossible but believed there must be a void surrounding the cosmos. Hero of Alexandria agreed that there are no naturally occurring vacuums but believed that they can be formed artificially. He cites pumps and siphons as evidence that voids can be created. Hero believed that bodies have a natural horror of vacuums and struggle to prevent their formation. You can feel the antipathy by trying to open a bellows that has had its air hole plugged. Try as you might, you cannot separate the sides. However, unlike Aristotle, Hero thought that if you and the bellows were tremendously strong, you could separate the sides and create a vacuum.