To this it may be objected: How can some fragments of air fill a theatre in which there is an infinite company of persons.

The Stoics, that the air is not composed of small fragments, but is a continued body and nowhere admits a vacuum; and being struck with the air, it is infinitely moved in waves and in right circles, until it fill that air which surrounds it; as we see in a fish-pool which we smite by a falling stone cast upon it; yet the air is moved spherically, the water orbicularly.

Anaxagoras says a voice is then formed when upon a solid air the breath is incident, which being repercussed is carried to the ears; after the same manner the echo is produced..