for which reason that nature loses some of its first
virtue. There is in addition to these a third difficulty, and this is
that a body of this kind, made of air and assumed by the spirits, is
exposed to the penetrating winds which continually sunder and scatter
the united portions of the air, eddying and whirling amidst the rest of
the atmosphere; therefore the spirit who would pervade {187} this air
would be dismembered or rent and broken up with the rending of the air
of which it formed part.

108.

It is impossible that the spirit, incorporated with a certain quantity
of air, should move this air; and this is proved by the passage where
it is said that "the spirit rarefies that portion of the air with which
it is mingled." This air therefore will rise high above the other air,
and the air will be set in motion by its own lightness and not by the
volition of the spirit, and if this air encounters a wind, the air will
be moved by the wind and not by the spirit which is incorporated in it.

[Sidenote: Can the Spirit speak?]

109.

In order to show whether the spirit can speak or not it is first
necessary to define the voice and the manner of its origin. The
following will be our definition: The voice is the movement of air in
friction against a dense body, or a dense body in friction against the
air (which is the same idea), and by this friction of the dense and the
rare what is rare is condensed, and resistance is caused; and again,
when the rare in swift motion and the rare in slow motion come into
contact, they condense one another and produce sound, and a great noise
is made. The sound or murmur made by the rare moving through the rare
{188} with slow motion is like the great flame whence sounds issue in
the air; the exceedingly great noise made by the rare, when the air
which is rare and swift mingles with that which is rare and in [slow]
motion, is like the flame of fire issuing from a great gun and striking
against the air; likewise the flame when it issues from a cloud strikes
the air as it begets the thunderbolt. Therefore we will say that the
spirit cannot produce a voice unless the air be set in motion, but
since there is no air within, it cannot discharge what it does not
possess; and if it wishes to move that air in which it is incorporated,
it is necessary that the spirit should multiply itself; but that which
has no quantity cannot be multiplied. In the fourth place it is said,
that no ra