The proceedings of scientific societies teem with such facts and
"working hypotheses," and the best of them have been collected by Miss
Clerke in her _History of Astronomy during the Nineteenth Century_. As
to established facts, we learn from the spectroscopic researches (1)
that the continuous spectrum is derived from the _photosphere_ or
solar gaseous material compressed almost to liquid consistency; (2)
that the _reversing layer_ surrounds it and gives rise to black
lines in the spectrum; that the _chromosphere_ surrounds this, is
composed mainly of hydrogen, and is the cause of the red prominences
in eclipses; and that the gaseous _corona_ surrounds all of
these, and extends to vast distances outside the sun's visible
surface.


FOOTNOTES:

[1] _Rosa Ursina_, by C. Scheiner, _fol_.; Bracciani, 1630.

[2] _R. S. Phil. Trans_., 1774.

[3] _Ibid_, 1783.

[4] _Observations on the Spots on the Sun, etc.,_ 4 degrees; London and
Edinburgh, 1863.

[5] _Periodicitat der Sonnenflecken. Astron. Nach. XXI._, 1844,
P. 234.

[6] _R.S. Phil. Trans._ (ser. A), 1906, p. 69-100.