is a curious fact that terrestrial magnetism and the boreal auroras
exhibit an oscillation parallel to that of the solar spots, and
apparently the same occurs with regard to temperature.

We must regard our sun as a globe of gas in a state of combustion,
burning at high temperature, and giving off a prodigious amount of heat
and light. The dazzling surface of this globe is called a _photosphere_
(light sphere). It is in perpetual motion, like the waves of an ocean of
fire, whose roseate and transparent flames measure some 15,000
kilometers (9,300 miles) in height. This stratum of rose-colored flames
has received the name of _chromosphere_ (color sphere). It is
transparent; it is not directly visible, but is seen only during the
total eclipses of the Sun, when the dazzling disk of that luminary is
entirely concealed by the Moon; or with the aid of the spectroscope. The
part of the Sun that we see is its luminous surface, or photosphere.

From this agitated surface there is a constant ejection of gigantic
eruptions, immense jets of flame, geysers of fire, projected at a
terrific speed to prodigious heights.

For years astronomers were greatly perplexed as to the nature of these
incandescent masses, known as prominences, which shot out like
fireworks, and were only visible during the total eclipses of the Sun.
But now, thanks to an ingenious invention of Janssen and Lockyer, these
eruptions can be observed every day in the spectroscope, and have been
registered since 1868, more particularly in Rome and in Catania, where
the Society of Spectroscopists was founded with this especial object,
and publishes monthly bulletins in statistics of the health of the Sun.

These prominences assume all imaginable forms, and often resemble our
own storm-clouds; they rise above the chromosphere with incredible
velocity, often exceeding 200 kilometers (124 miles) per second, and
are carried up to the amazing height of 300,000 kilometers (186,000
miles).

[Illustration: FIG. 31.--Rose-colored solar flames 228,000 kilometers
(141,500 miles) in height, _i.e._, 18 times the diameter of the Earth.]

The Sun is surrounded with these enormous flames on every side;
sometimes they shoot out into space like splendid curving roseate
plumes; at others they rear their luminous heads in the Heavens, like
the cleft and waving leaves of giant palm-trees. Having illustrated a
remarkable type of solar spot, it is interesting to submit to the reader
a