is
not, does not make sharp shadows.

240. Pokers and lifters for stove lids often have open spiral
handles.

SECTION 27. _Color._

What makes the ocean look green in some places and blue in
others?

What makes the sky blue?

What causes material to be colored?

What makes a rainbow?

What is color?

[Illustration: FIG. 90. Making a rainbow on the wall.]

Color is merely a kind of light. We say that a sweater is red; really
the sweater is not red, but the light that it reflects to our eyes is
red. We speak of a piece of red glass, but the glass is not red; it is
the light that it lets pass through it that is red.

White is not really a color; _all_ colors put together make white.
Experiments 50 and 51 will prove this.

[Illustration: FIG. 91. The prism separates the white light into the
rainbow colors.]

EXPERIMENT 50. Hold a prism in the sunlight by the window
and make a "rainbow" on the wall. The diagram here shown
illustrates how the prism breaks up the single beam of white
light into different-colored beams of light.

[Illustration: FIG. 92. When the wheel is rapidly whirled the colors
blend to make white.]

EXPERIMENT 51. Rotate the color disk on the rotator and watch
it. Make it go faster and faster until all the colors are
perfectly merged. What color do you get by combining all
the colors of the rainbow? If the colors on the disk were
perfectly clear rainbow colors, in exactly the same proportion
as in the rainbow, the whirling would give a white of dazzling
purity.

Since you can break up pure white light into all the colors, and since
you can combine all the colors and get pure white light, it is clear
that white light is made up of all the colors.

* * * * *

As we have already said, light is probably vibrations or waves of
ether. Light made of the longest waves that we can see is red. If the
waves are a little shorter, the light is orange; if they are shorter
yet, it is yellow; still shorter, green; shorter still, blue; while
the shortest waves that we can see are those of violet light. Black
is not a color at all; it is the absence of light. We say the night
is black when we cannot see anything. A deep hole looks black because
practically no light is reflected up from its depths. When you "see"
anything black, you really see the things around it and the parts of
it that