the more tranquil kind. Eruptive or explosive by origin,
they occur in close connection with spots; whether causally, the
materials ejected as "flames" cooling and settling down as dark,
depressed patches of increased absorption;[615] or consequentially, as a
reactive effect of falls of solidified substances from great heights in
the solar atmosphere.[616] The two classes of phenomena, at any rate,
stand in a most intimate relation; they obey the same law of
periodicity, and are confined to the same portions of the sun's surface,
while quiescent prominences may be found right up to the poles and close
to the equator.

The general distribution of prominences, including both genera, follows
that of faculae much more closely than that of spots. From Father
Secchi's and Professor Respighi's observations, 1869-71, were derived
the first clear ideas on the subject, which have been supplemented and
modified by the later researches of Professors Tacchini and Ricco at
Rome and Palermo. The results are somewhat complicated, but may be
stated broadly as follows. The district of greatest prominence-frequency
covers and overlaps by several degrees that of the greatest
spot-frequency. That is to say, it extends to about 40 deg. north and
south of the equator.[617] There is a visible tendency to a second pair
of maxima nearer the poles. The poles themselves, as well as the equator,
are regions of minimum occurrence. Distribution in time is governed by
the spot-cycle, but the maximum lasts longer for prominences than for
spots.

The structure of the chromosphere was investigated in 1869 and
subsequent years by Professor Respighi, director of the Capitoline
Observatory, as well as by Spoerer, and Bredikhine of the Moscow
Observatory. They found this supposed solar envelope to be of the same
eruptive nature as the vast protrusions from it, and to be made up of a
congeries of minute flames[618] set close together like blades of grass.
"The appearance," Professor Young writes,[619] "which probably indicates
a fact, is as if countless jets of heated gas were issuing through vents
and spiracles over the whole surface, thus clothing it with flame which
heaves and tosses like the blaze of a conflagration."

The summits of these filaments of fire are commonly inclined, as if by a
wind sweeping over them, when the sun's activity is near its height, but
erect during his phase of tranquillity. Spoerer, in 1871, inferred the
influence of perman