1. When we supped with Ammonius at Athens, who was then the third time captain of the city-bands, there was a great noise about the house, some without doors calling, Captain! Captain! After he had sent his officers to quiet the tumult, and had dispersed the crowd, we began to enquire what was the reason that those that are within doors hear those that are without, but those that are without cannot hear those that are within as well. And Ammonius said, that Aristotle had given a reason for that already; for the sound of those within, being carried without into a large tract of air, grows weaker presently and is lost; but that which comes in from without is not subject to the like casualty, but is kept close, and is therefore more easy to be heard. But that seemed a more difficult question, Why sounds seem greater in the night than in the day, and yet altogether as clear. For my own part (continued he) I think Providence hath very wisely contrived that our hearing should be quickest when our sight can do us very little or no service; for the air of the “blind and solitary Night,” as Empedocles calls it, being dark, supplies in the ears that defect of sense which it makes in the eyes. But since of natural effects we should endeavor to find the causes, and to discover what are the material and mechanical principles of things is the proper task of a natural philosopher, who shall first assist us with a rational account hereof? 2. Boethus began, and said: When I was a novice in letters, I then made use of geometrical postulates, and assumed as undoubted truths some undemonstrated suppositions; and now I shall make use of some propositions which Epicurus hath demonstrated already. Bodies move in a vacuum, and there are a great many spaces interspersed among the atoms of the air. Now when the air being rarefied is more extended, so as to fill the empty space, there are but few vacuities scattered and interspersed among the particles of matter; but when the atoms of air are condensed and laid close together, they leave a vast empty space, convenient and sufficient for other bodies to pass through. Now the coldness of the night makes such a constipation. Heat opens and separates the parts of condensed bodies. Therefore bodies that boil, grow soft, or melt, require a greater space than before; but on the contrary, the parts of the body that are condensed or freeze are contracted closer to one another, and leave those vessels and places from which they retired partly empty. Now the voice, meeting and striking against a great many bodies in its way, is either altogether lost or scattered, and very much and very frequently hindered in its passage; but when it hath a plain and smooth way through an empty space, and comes to the ear uninterrupted, the passage is so sudden, that it preserves its articulate distinctness, as well as the words it carries. You may observe that empty vessels, when knocked, answer