ry which arrests the motion of the clouds in the air. Where there
is life there is heat, where there is vital heat there is movement of
moisture.

[Sidenote: Against those desiring to correct Nature]

86.

The act of cutting out the nostrils of a horse is a piece of ludicrous
folly. And the foolish indulge in this practice as though they
considered nature had failed to supply necessary wants, and man had
therefore to supplement her work. Nature made two apertures in the
nose, which each in {176} itself is half as large as the lung pipe
whence breath proceeds, and if these apertures did not exist the mouth
would abundantly suffice for breathing purposes. And if you said to
me, Why has nature thus provided animals with nostrils if respiration
through the mouth is sufficient?--I would answer that nostrils are made
to be used when the mouth is employed in masticating its food.

[Sidenote: Of Trees]

87.

If a tree has been stripped of its bark in some spot, nature makes
provision for this and gives a greater supply of nourishing sap to the
stripped portion than to any other, so that in place of what has been
taken away the bark grows thicker than in any other spot. And so
impetuous is the motion of the sap that when it reaches the spot which
is to be healed, it rises higher like a bounding ball, in bubbles, not
unlike boiling water.

[Sidenote: The Leaves of Plants]

88.

Nature has so placed the leaves of the latest shoots of many trees that
the sixth leaf is always above the first, and thus in continued
succession unless the rule is obstructed. And this she has done for
two useful purposes in the plant: firstly, since the branches and the
fruit of the following year spring from the bud or eye which is above
and in contact with the juncture of the leaves, {177} the water which
feeds the shoot may be able to run down and nourish the bud, through
the drop being caught in the hollow whence the leaf springs. And the
second advantage is that as these buds shoot in the following year, one
will not be covered by the other, since the five shoots spring on five
different sides.

[Sidenote: From Known to Unknown]

89.

In order to arrive at knowledge of the motions of birds in the air, it
is first necessary to acquire knowledge of the winds, which we will
prove by the motions of water in itself, and this knowledge will be a
step enabling us to arrive at the knowledge of beings that fly between
the ai