body set in motion continues to move
as long as the impression of the motive power lasts in it.

[Sidenote: Can Man imitate a Bird's Flight?]

22.

The bird is an instrument which operates by mathematical laws, and man
can reproduce all {150} the movements of this instrument, but cannot
attain to the intensity of its power; and can only succeed in acquiring
balance. Thus we will say that such an instrument constructed by man
lacks only the soul of the bird, and the soul of man must counterfeit
the soul of the bird. The spirit in the frame of the bird doubtless
would respond to needs of that frame better than would the spirit of
man, whose frame is different, more especially in the almost insensible
motions of balance; and since we see the bird make provision for the
many sensible varieties of movement, we can conclude by such experience
that man can acquire knowledge of the more markedly sensible of these
movements, and that he will be able to make ample provision against the
destruction of that instrument of which he has made himself the spirit
and the guide.

[Sidenote: Of Inertia]

23.

A natural and continuous motion seeks to preserve its course along the
line of its starting-point, that is to say, let us call starting-point
whatever place in which it varies.

24.

Everything maintains itself by motion. And if it were possible to
describe a diameter of air on the sphere of the earth, like to a well,
which would extend from one superficies to the other, {151} and if a
weighty body were dropped into this well, the body would seek to remain
stationary at the centre, but so strong would be the impetus that for
many years it would prevent it from so doing.

[Sidenote: Transmission of Motion]

25.

Impetus is a virtue created by motion and communicated by the motive
force to the object moved, and this object acquires motion in
proportion to the energy of the impetus.

[Sidenote: Matter is Inert]

26.

No lifeless matter moves of itself, but its motion is caused from
without.

27.

All elements displaced from their natural place seek to return to it,
and more especially fire, water and earth.

28.

All matter universally seeks to maintain itself in its natural state;
hence, water in motion seeks to maintain its course according to the
force by which it is propelled, and if it meets with opposition it
finishes the length of the course it began in a circular and reflex
motion.