f Analysis]

71.

We know definitely that sight is infinitely swift and in an instant of
time perceives countless shapes, nevertheless it only sees one object
at a time. Let us take an example. You, O reader, will see the whole
of this written page at a glance, and you will instantly realize that
it is full of various letters, but you will not realize at that moment
what these letters are nor what they signify; wherefore you will have
to proceed word by word and line by line to take cognizance of these
letters. Again, if you wish to reach the summit of a building you must
mount step by step, {170} otherwise it will be impossible for you to
reach the summit. And therefore I say to you whom nature has drawn to
this art, if you wish to attain to a thorough knowledge of the forms of
objects, you will begin by studying the details, and not proceed to the
second until you have committed the first to memory and mastered it in
practice, and if you do otherwise you will be wasting your time and
protracting your studies. And remember first of all to acquire
diligence, which signifies speed.

[Sidenote: Vision]

72.

Of the nature of the eye. Here are the forms, here the colours, here
the form of every part of the universe are concentrated in a point, and
that point is so great a marvel! O marvellous and stupendous
necessity! thou dost compel by thy law, and by the most direct path,
every effect to proceed from its cause. These things are verily
miracles! I wrote in my Anatomy how in so small a space the visual
faculty can be reproduced and formed again in its whole expanse.

73.

In many cases one and the same thing is attracted by two violent
forces,--necessity and power. The water falls in rain and by necessity
the earth absorbs the humidity; the sun causes it to evaporate, not of
necessity, but by power.

{171}

[Sidenote: Unconscious Reasoning]

74.

The pupil of the eye in the air expands and contracts according to
every degree of motion made by the sun. And with every dilation or
contraction the same object will appear of a different size, although
frequently the relative scale of surrounding circumstances does not
allow us to perceive these variations in any single object we look at.

[Sidenote: The Eye]

75.

The pupil of the eye dilates and contracts in proportion to the variety
of bright and dark objects which are reflected in it. In this case
nature has afforded compensation to th