d places
from which they retired partly empty. Now the sound, 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 presently, send
out a noise to a great distance, and oftentimes the sound whirled round
in the hollow breaks out with a considerable force; whilst a vessel
that is filled either with a liquid or a solid body will not answer to
a stroke, because the sound hath no room or passage to come through. And
among solid bodies themselves, gold and stone, because they want pores,
can hardly be made to sound; and when a noise is made by a stroke upon
them, it is very flat, and presently lost. But brass is sounding, it
being a porous, rare, and light metal, not consisting of parts tightly
compacted, but being mixed with a yielding and uncompacted substance,
which gives free passage to other motions, and kindly receiving the
sound sends it forward; till some touching the instrument do, as it
were, seize on it in the way, and stop the hollow; for then, by reason
of the hindering force, it stops and goes no further. And this, in my
opinion, is the reason why the night is more sonorous, and the day less;
since in the day, the heat rarefying the air makes the empty spaces
between the particles to be very little. But, pray, let none argue
against the suppositions I assumed.

And I (Ammonius bidding me oppose him) said: Sir, your suppositions
which demand a vacuum to be granted I shall admit; but you err in
supposing that a vacuum is conducive either to the preservation or
conveyance of sound. For that which cannot be touched, acted upon, or
struck is peculiarly favorable to silence. But sound is a stroke of a
sounding body; and a sounding body is that which has homogeneousness and
uniformity, and is easy to be moved, light, smooth, and, by reason of
its tenseness and continuity, it is obedient to the stroke; and such is
the air. Water, earth, and fire are of themselves soundless; but each of
them makes a noise when air falls upon or gets into it. And brass hath
no vacuum; but being mixed with a smooth and gentle air it answers to a
stroke, and is sounding. If the