cant importance, may just serve to turn the scale. A new
type may be formed in which the variation in question is preserved and
augmented; its stability may increase and in time a new species may be
produced.

At the risk of condemnation as a wanderer beyond my province into the
region of biological evolution, I would say that this view accords with
what I understand to be the views of some naturalists, who recognise the
existence of critical periods in biological history at which extinction
occurs or which form the starting-point for the formation of new
species. Ought we not then to expect that long periods will elapse
during which a type of animal will remain almost constant, followed by
other periods, enormously long no doubt as measured in the life of man,
of acute struggle for existence when the type will change more rapidly?
This at least is the view suggested by the theory of stability in
the physical universe. (I make no claim to extensive reading on this
subject, but refer the reader for example to a paper by Professor A.A.W.
Hubrecht on "De Vries's theory of Mutations", "Popular Science Monthly",
July 1904, especially to page 213.)

And now I propose to apply these ideas of stability to the theory of
stellar evolution, and finally to illustrate them by certain recent
observations of a very remarkable character.

Stars and planets are formed of materials which yield to the enormous
forces called into play by gravity and rotation. This is obviously true
if they are gaseous or fluid, and even solid matter becomes plastic
under sufficiently great stresses. Nothing approaching a complete study
of the equilibrium of a heterogeneous star has yet been found possible,
and we are driven to consider only bodies of simpler construction. I
shall begin therefore by explaining what is known about the shapes which
may be assumed by a mass of incompressible liquid of uniform density
under the influences of gravity and of rotation. Such a liquid mass may
be regarded as an ideal star, which resembles a real star in the fact
that it is formed of gravitating and rotating matter, and because its
shape results from the forces to which it is subject. It is unlike a
star in that it possesses the attributes of incompressibility and
of uniform density. The difference between the real and the ideal is
doubtless great, yet the similarity is great enough to allow us
to extend many of the conclusions as to ideal liquid stars to the
cond