e visual faculty by contracting
the pupil of the eye when it is offended by excess of light and by
causing it to dilate when offended by excess of darkness, like the
opening of the purse. And nature here behaves like the man who has too
much light in his house and closes half the window, or more or less of
it according to need; and when night comes he opens the window
altogether so as to see better inside his house, and nature here adopts
a continued process of compensation, by continually regulating and
readjusting the expansion and contracting of the pupil, in proportion
to the aforesaid obscurity and light which are continually reflected in
it.

{172}

[Sidenote: Water surrounding the Globe Spherical]

76.

When you collect facts relating to the science of the motion of water,
remember to place under every proposition the uses to which it may be
applied, in order that this knowledge may not be fruitless.

77.

This is a difficult question to answer, but I will nevertheless state
my opinion. Water, which is clothed with air, desires naturally to
cleave to its sphere because in this position it is without gravity.
This gravity is twofold,--the gravity of the whole which tends to the
centre of the elements, and the gravity which tends to the centre of
the waters of the spherical orb; if this were not so the water would
form a half sphere only, which is the sphere described from the centre
upwards. But I see no means in the human mind of acquiring knowledge
with regard to this. We must say, as we say of the magnet which
attracts iron, that such a virtue is an occult property of which there
is an infinite quantity in nature.

78.

In the motion of earth against earth the repercussion of the portion
struck is slight.

Water struck by water, eddies in circles around the spot where the
shock has taken place.

The reverberation of the voice continues for a {173} great distance
through the air; for a greater distance through fire. The mind travels
for a still greater distance through the universe; but since it is
finite it does not penetrate into infinity.

79.

If the water which rises on the summits of the mountains comes from the
sea, whence it is propelled by its weight to a greater height than that
of the mountains, why has this portion of the element of water the
power to elevate itself to such an altitude and to penetrate the earth
by so great an expenditure of labour and time, when the re