lines being also well seen, though they are not specially conspicuous.
Among the very numerous stars of this group are Capella, Aldebaran,
Arcturus, Pollux, etc. The spectra of these stars are in fact
practically identical with the spectrum of our own sun, as shown, for
instance, by Dr. Scheiner, of the Potsdam Astrophysical Observatory, who
has measured several hundred lines on photographs of the spectrum of
Capella, and found a very close agreement between these lines and
corresponding ones in the solar spectrum. We can hardly doubt that the
physical constitution of these stars is very similar to that of our sun.
This cannot be the case with the stars of the second subdivision (II.b),
the spectra of which are very complex, each consisting of a continuous
spectrum crossed by numerous dark lines, on which is superposed a second
spectrum of bright lines. Upwards of seventy stars are known to possess
this extraordinary spectrum, the only bright one among them being a star
of the third magnitude in the southern constellation Argus. Here again
we have hydrogen and helium represented by bright lines, while the
origin of the remaining bright lines is doubtful. With regard to the
physical constitution of the stars of this group it is very difficult to
come to a definite conclusion, but it would seem not unlikely that we
have here to do with stars which are not only surrounded by an
atmosphere of lower temperature, causing the dark lines, but which,
outside of that, have an enormous envelope of hydrogen and other gases.
In one star at least of this group Professor Campbell, of the Lick
Observatory, has seen the F line as a long line extending a very
appreciable distance on each side of the continuous spectrum, and with
an open slit it was seen as a large circular disc about six seconds in
diameter; two other principal hydrogen lines showed the same appearance.
As far as this observation goes, the existence of an extensive gaseous
envelope surrounding the star seems to be indicated.

_Type III._ contains comparatively few stars, and the spectra are
characterised by numerous dark bands in addition to dark lines, while
the more refrangible parts are very faint, for which reason the stars
are more or less red in colour. This class has two strongly marked
subdivisions. In the first (III.a) the principal absorption lines
coincide with similar ones in the solar spectrum, but with great
differences as to intensity, many lines being mu