said, "Let there be light; and there was light" on the FIRST DAY, but it
was not until the FOURTH DAY that those great light-bearers--the sun and
the moon--were made lights to the earth, and set "for signs, and for
seasons, and for days and years." But the question, "What is light?" is not
one easily answered.

We can all understand that light is that which makes everything visible,
but you will perhaps be surprised to hear that it has taken a very long
time even to find out how the light comes to us.

It is now generally believed that light, which is one of the strongest
powers in the world, is caused by motion; and that it is because every
light-giving body is always moving very fast, that it gives out light. But
no one can explain how this rapid movement began, nor what that "ether" is
through which the "vibrations" travel until they reach a wonderful little
screen which we have at the back of each of our eyes, by means of which we
are able to see.

We may think of the air around us as a vast ocean, through which waves
conveying light and sound are constantly travelling. When a sound-wave
strikes the ear, we hear; when a light-wave, moving like a water-wave,
reaches the eye, we see. Light comes chiefly from the sun: it is beautiful
to think, is it not?--of waves of light streaming always, day and night,
from that wonderful sun so far away, and coming, wave after wave, to paint
beautiful pictures on our eyes! For if you and I both look at the same
lovely view, we have each a picture of it--the mountains, and sea, and
green fields, and houses--all to ourselves; and so it would be if, not two
people, but two hundred were looking. One thing about light of which we are
quite sure is, that it travels very quickly. It makes its noiseless journey
all round this great earth eight times in one second--in less time than it