silver spoon are very bright, and are clearly seen. Quicksilver
is put at the back of looking-glasses because it reflects so many
waves. It not only sends back those which come from the sun, but
those, too, which come from your face. So, when you see yourself
in a looking-glass, the sun-waves have first played on your face
and bounded off from it to the looking-glass; then, when they
strike the looking-glass, they are thrown back again on to the
retina of your eye, and you see your own face by means of the
very waves you threw off from it an instant before.

But the reflected light-waves do more for us than this. They not
only make us see things, but they make us see them in different
colours. What, you will ask, is this too the work of the
sunbeams? Certainly; for if the colour we see depends on the
size of the waves which come back to us, then we must see things
coloured differently according to the waves they send back. For
instance, imagine a sunbeam playing on a leaf: part of its waves
bound straight back from it to our eye and make us see the
surface of the leaf, but the rest go right into the leaf itself,
and there some of them are used up and kept prisoners. The red,
orange, yellow, blue, and violet waves are all useful to the
leaf, and it does not let them go again. But it cannot absorb
the green waves, and so it throws them back, and they travel to
your eye and make you see a green colour. So when you say a leaf
is green, you mean that the leaf does not want the green waves of
the sunbeam, but sends them back to you. In the same way the
scarlet geranium rejects the red waves; this table sends back
brown waves; a white tablecloth sends back nearly the whole of
the waves, and a black coat scarcely any. This is why, when
there is very little light in the room, you can see a white