exploration of that field is attained so
will our knowledge of the processes of cosmical evolution increase.

From the point of view of observation, improved methods in the use of
the spectroscope and increase of accuracy in photometry will certainly
lead to a great increase in our knowledge within the next few years.
Probably the observational advance will be more rapid than that of
theory, for we know how extraordinary has been the success attained
within the last few years, and the theory is one of extreme difficulty;
but the two ought to proceed together hand in hand. Human life is
too short to permit us to watch the leisurely procedure of cosmical
evolution, but the celestial museum contains so many exhibits that it
may become possible, by the aid of theory, to piece together bit by bit
the processes through which stars pass in the course of their evolution.

In the sketch which I have endeavoured to give of this fascinating
subject, I have led my reader to the very confines of our present
knowledge. It is not much more than a quarter of a century since this
class of observation has claimed the close attention of astronomers;
something considerable has been discovered already and there seems
scarcely a discernible limit to what will be known in this field a
century from now. Some of the results which I have set forth may then be
shown to be false, but it seems profoundly improbable that we are being
led astray by a Will-of-the-Wisp.

XXIX. THE EVOLUTION OF MATTER. By W.C.D. Whetham, M.A., F.R.S.

Trinity College, Cambridge.

The idea of evolution in the organic world, made intelligible by the
work of Charles Darwin, has little in common with the recent conception
of change in certain types of matter. The discovery that a process of
disintegration may take place in some at least of the chemical atoms,
previously believed to be indestructible and unalterable, has modified
our view of the physical universe, even as Darwin's scheme of the mode
of evolution changed the trend of thought concerning the organic world.
Both conceptions have in common the idea of change throughout extended
realms of space and time, and, therefore, it is perhaps not unfitting
that some account of the most recent physical discoveries should be
included in the present volume.

The earliest conception of the evolution of matter is found in the
speculation of the Greeks. Leucippus and Democritus imagined unchanging
eternal atoms, He