Humboldt speaks
of a mysterious connexion between volcanoes and rain, and says that when
a volcano bursts out in South America in a dry season, it sometimes
changes it to a rainy one. The Indians of Paraguay, when their crops are
threatened by drought, set fire to the vast plains with the intention of
producing rain. In Louisiana, heavy rains have been known from time
immemorial to succeed the conflagration of the prairies; and the
inhabitants of Nova Scotia bear testimony to a similar result from the
burning of their forests. Great battles are said to produce rain, and it
is even stated that the spread of manufactures in a particular district
deteriorates the climate of such district, the ascending current
occasioned by the tall chimney of every manufactory tending to produce
rain. In Manchester, for example, it is said to rain six days out of
seven.

[Picture: Decorative picture of person by pool]

[Picture: Decorative picture of pastoral scene with rainbow]

CHAPTER VI.

THE RAINBOW--DECOMPOSITION OF WHITE LIGHT BY THE PRISM--FORMATION OF
PRIMARY AND SECONDARY BOWS--RAINBOWS IN MOUNTAIN REGIONS--THE RAINBOW A
SACRED EMBLEM--LUNAR RAINBOW--LIGHT DECOMPOSED BY CLOUDS--THEIR BEAUTIFUL
COLOURS--EXAMPLES.

By means of rain and rain clouds we get that beautiful appearance so well
known as the rainbow. In order to form some idea of the manner in which
the rainbow is produced, it is necessary to know something of the manner
in which light is composed. Sir Isaac Newton was the first philosopher
who clearly explained the composition of light, as derived from the sun.
He admitted a ray of the sun into a darkened room through a small hole in
the window shutters; in front of this hole he placed a glass prism, and
at a considerable distance behind the prism he placed a white screen. If
there had been no prism between the hole and the screen, the ray of light
would have proceeded in the direction of the dotted lines, and a bright
spot would have fallen upon the floor of the room, as shown in the
figure. But the effect of the prism is to refract or bend the ray out of
its ordinary course, and in doing so it does not produce a white spot
upon the screen, but a long streak of beautiful colours, in the order
marked in the figure, red being at the bottom, then orange, yellow,
green, blue, indigo, and violet at the top.

[Picture: Decomposition of white light]

In order to acco