WHY BODIES OF WATER LOOK GREEN IN SOME PLACES AND BLUE IN OTHERS.
Water acts in a similar way, but it lets the green light through
instead of the blue. A little water holds back (absorbs) the other
colors so slightly that you cannot notice the effect in a glass of
water. But in a swimming tank full of water, or in a lake or an ocean,
you can notice it decidedly when you look straight down into the water
itself.

When you look at a smooth body of water at a slant on a clear day,
the blue sky is reflected to you and the water looks blue instead of
green. And it may even look blue when you look straight down in it if
it is too deep for you to see the bottom and the sky is reflected from
the surface.

WHY THE SKY IS OFTEN RED AT SUNSET. Dust lets more of red and yellow
light through than of any other color, and for this reason there is
much red and yellow in the sunset. Just before the sun sets, it shines
through the low, dusty air. The dust filters out most of the light
except the red and yellow. The red light and yellow light are
reflected by the clouds (for the clouds are themselves "white"; that
is, they reflect all the colors that strike them), and you have the
beautiful sunset clouds. Sometimes there is a purple in the sunset,
and even green. But since the air itself is blue (that is, it lets
mostly blue light go through), it is easy to see how this blue can
combine with the red or yellow that the dust lets through, to form
purple or green.

But we could not have sunset colors or all the colors we see on earth,
if it were not that the sunlight is mostly white--that it contains all
colors. And that, too, is why we can have a rainbow.

HOW RAINBOWS ARE FORMED. You already know fairly well how a rainbow
is formed, since you made an imitation of one with a prism. A rainbow
appears in the sky when the sun shines through the rain; the plain
white light of the sun is divided up into red, orange, yellow, green,
blue, indigo, and violet. As the white light of the sun passes through
the raindrops, the violet part of the light is bent more than any of
the rest, the indigo part is bent not quite so much, and so on to the
red, which is bent least of all. So all the colors fan out from the
single beam of white light and form a band of color, which we call the
rainbow.

[Illustration: FIG. 95. Explain why the breakers are white and the sea
green or blue.]

HOW WE CAN TELL WHAT THE SUN AND STARS ARE MADE OF. When a gas or