DEMUS.

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 inquire
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 give us a
rational account hereof?

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 vacant space, there are only a 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 parts of condensed bodies, and 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 an