third part of Nature, and miss two-thirds. The best scholar is he whose
eye is so keen as to see at once how the thing looks, and who need not,
therefore, trouble himself with any reasons why it looks so: but few
people have this acuteness of perception; and to those who are destitute
of it, a little pointing out of rule and reason will be a help,
especially when a master is not near them. I never allow my own pupils
to ask the reason of anything, because, as I watch their work, I can
always show them how the thing is, and what appearance they are missing
in it; but when a master is not by to direct the sight, science may,
here and there, be allowed to do so in his stead.

Generally, then, every solid illumined object--for instance, the stone
you are drawing--has a light side turned towards the light, a dark side
turned away from the light, and a shadow, which is cast on something
else (as by the stone on the paper it is set upon). You may sometimes be
placed so as to see only the light side and shadow, and sometimes only
the dark side and shadow, and sometimes both, or either, without the
shadow; but in most positions solid objects will show all the three, as
the stone does here.

Hold up your hand with the edge of it towards you, as you sit now with
your side to the window, so that the flat of your hand is turned to the
window. You will see one side of your hand distinctly lighted, the other
distinctly in shade. Here are light side and dark side, with no seen
shadow; the shadow being detached, perhaps on the table, perhaps on the
other side of the room; you need not look for it at present.

Take a sheet of note-paper, and holding it edgeways, as you hold your
hand, wave it up and down past the side of your hand which is turned
from the light, the paper being, of course, farther from the window. You
will see, as it passes a strong gleam of light strike on your hand, and
light it considerably on its dark side. This light is _reflected_ light.
It is thrown back from the paper (on which it strikes first in coming
from the window) to the surface of your hand, just as a ball would be if
somebody threw it through the window at the wall and you caught it at
the rebound.

Next, instead of the note-paper, take a red book, or a piece of scarlet
cloth. You will see that the gleam of light falling on your hand, as you
wave the book is now reddened. Take a blue book, and you will find the
gleam is blue. Thus every object will ca