undant
profusion everywhere. Magnificent showers fell at intervals, and the
rainbows, more beautiful than any they had ever heretofore seen, spanned
the heavens after the showers.

This had been noticed during the previous year, but now, after nine
months of their life, with the wonderful insight which their needs had
instilled into them, made them very observant of every phenomenon.

"I have often wondered," observed George, as he gazed at the beautiful
broad band which formed a crescent across the heavens, "why there are
never any rainbows in the middle of the day. They are never seen except
in the morning or in the evening, and usually only in the evening."

"In order to understand that it will be necessary to explain what a
rainbow is. As I stated previously, light is merely vibration. Now
colors are formed by the different lengths of the vibrations, just the
same as the different musical notes are made by the different vibratory
lengths. To understand this more fully, I make a sketch (Fig. 7), which
shows just what I mean. You will see that red is the lowest musical
pitch, which we will call C, and to the right is a long, wavy line. D,
the next pitch higher, might resemble orange, with the wavy line a
little shorter, and so on, until we reach the highest note in the scale,
where the wave lengths are very short. You have probably noticed that a
drop of water in the sunshine glistens, and, if closely observed, may
have seen that it was colored, particularly blue or green. As the rays
of the sun strike the globe of water, they produce different wave
lengths, and in that way make it appear to you as being possessed of
colors. Now, a rainbow is nothing more nor less than sunlight passing
through the drops of water which are suspended in the air and causing a
refraction of the light. At noon the sun shines down from overhead, and
we are not in the proper position to see this refracted light; but in
the morning or in the evening the sun shines against the earth at an
angle. At those times we are able to see the effect of refraction by the
colors produced.

[Illustration: _Fig. 7. THE COLOR SPECTRUM_]

[Illustration: _Fig. 8. REFLECTION ANGLE_]

"When you throw a ball against a wall at an angle, it bounds away at the
same angle. That is reflection, and is just exactly what light does when
a ray strikes a mirror. If, on the other hand, the glass had no mercury
on it to reflect the light, the ray would not go straight