n another way, given the date of
a coming total eclipse we can predict to a certain extent the probable
shape and character of the Corona if we know how the forthcoming date
stands as regards a Sun-spot maximum or minimum.

The most recent important eclipses up to date which have been observed,
namely those of April 16, 1893, Aug. 9, 1896, and Jan. 21, 1898, do not
add much to our useful records of the outward appearances presented by
the Corona. The 1896 Corona is described as intermediate between the two
Types respectively associated with years of maximum and minimum
Sun-spots, and this is as it should have been, albeit there was one
extension which reached to about two diameters of the Sun. The 1898
Corona yielded four long Coronal streamers reaching much farther from
the Sun than any previously seen, the two longest reaching to 41/2 and 6
diameters of the Sun respectively. These dimensions are quite
unprecedented.

[Illustration: FIG. 10.--CORONA OF 1882. (SUN-SPOT MAXIMUM.)]

The application of the spectroscope to observations of eclipses of the
Sun demands a few words of notice in this place, but it would not be
consistent with the plan of this work to go into details. Though the
spectroscope has been applied under many different circumstances to
different parts of the Sun's surroundings in connection with total
eclipses yet it is in regard to the Corona that most has been done and
most has been discovered. The substance of the discoveries made is that
the Corona shines with an intrinsic light of its own, that is to say,
that it is composed of constituents whose temperature is sufficiently
elevated to be self-luminous. These constituents are chiefly hydrogen;
the body which corresponds to the line D3 (of Fraunhofer's scale), and
which has been named "Helium"; and the body which corresponds to the
bright green line 1474 of Kirchoff's scale and which, since its
existence was first suspected and then assured, has been named
"Coronium."

The reader will not be surprised to learn, from what has gone before,
that an immense mass of records have accumulated respecting the
appearance of the Corona. Correspondingly numerous and divergent are the
theories which have been launched to explain the observations made. One
thing is in the highest degree probable, namely, that electricity is
largely concerned.

Going back to the question of Sun-spots regarded in their possible or
probable association with the Corona, the pre