The name is absent

60 Recent Advances in Stellar Astronomy

But the giant stars, being far brighter, can be seen at
great distances. We are fishing for them in much wider
waters, and naturally we catch more. The most striking
instance is afforded by the M stars. Here the dwarfs are
so faint that not one of them is visible to the naked eye,
though three of the four nearest stars belong to this class,
and our naked-eye list is composed exclusively of giant
M’s, though there are probably more than a hundred
dwarf M’s which are nearer us than any of these giants.
Among the К-stars, only a few of the nearest dwarfs are
visible to the unaided eye, while the proportion among
the G’s is larger. We are therefore dealing with com-
plex mixtures, composed of giants and dwarfs in different
proportions for the different spectral types, and the aver-
age parallax, proper motion, or what not, of the stars
selected in this curious way may be very far indeed from
representing the average of the stars of the same type
in a given region of space. Indeed, different methods
of selection—for example, the rejection of the stars of
large proper motion—may greatly change the relative
proportion of giants and dwarfs in our mixture, and there-
fore the calculated characteristics of the “average star.”
Much care is necessary in interpreting such averages,
for the effects of this “involuntary selection” are often
far-reaching and unexpected.

One would naturally expect that these great differences
in absolute magnitude, among stars of the same spectral
class, would be associated with differences in the spectra
themselves. From what has already been said, no large
differences can be anticipated; but smaller differences exist,
and are of much importance. Here again Hertzsprung
was the first in the field—pointing out, as long ago as
1905, that certain stars, in whose spectra Miss Maury, at

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