Heronis Alexandrini spiritalium liber

other augmentation be conceived by the mind to happen to them. From which it is clear that in the bodies of air there are certain vacuums disseminated in between, and when some force arrives, they yield into the vacuums against nature; but the air which is in a vessel inverted into water is not greatly compressed. For that which exerts force to effect this is not at all suitable, since naturally water itself has neither weight nor vehement compression in itself. Wherefore, it happens that those diving into the deep of the sea, having infinite metretae large units of measure over their shoulders, are not compelled to breathe by the water, since very little air is contained in the nostrils at all. But what the cause may be, why those who swim in the deep, as has been said, having an infinite weight of water over their shoulders, are not compressed, seems worthy of consideration. Therefore, some say it is because it is of equal weight in accordance with itself; but these say nothing regarding why those who swim downward are not compressed by the water above. Therefore, let that be demonstrated in this way.