racleitus held that all things were in a continual
state of flux--Panta rei.

But no one in the Ancient World--no one till quite modern times--could
appreciate the strength of the position which the theory of the
evolution of matter must carry before it wins the day. Vague
speculation, even by the acute minds of philosophers, is of little use
in physical science before experimental facts are available. The true
problems at issue cannot even be formulated, much less solved, till the
humble task of the observer and experimenter has given us a knowledge of
the phenomena to be explained.

It was only through the atomic theory, at first apparently diametrically
opposed to it, that the conception of evolution in the physical world
was to gain an established place. For a century the atomic theory, when
put into a modern form by Dalton, led farther and farther away from
the idea of change in matter. The chemical elements seemed quite
unalterable, and the atoms, of which each element in modern view is
composed, bore to Clerk Maxwell, writing about 1870, "the stamp of
manufactured articles" exactly similar in kind, unchanging, eternal.

Nevertheless throughout these years, on the whole so unfavourable to its
existence, there persisted the idea of a common origin of the distinct
kinds of matter known to chemists. Indeed, this idea of unity in
substance in nature seems to accord with some innate desire or intimate
structure of the human mind. As Mr Arthur Balfour well puts it, "There
is no a priori reason that I know of for expecting that the material
world should be a modification of a single medium, rather than a
composite structure built out of sixty or seventy elementary substances,
eternal and eternally different. Why then should we feel content with
the first hypothesis and not with the second? Yet so it is. Men of
science have always been restive under the multiplication of entities.
They have eagerly watched for any sign that the different chemical
elements own a common origin, and are all compounded out of some
primordial substance. Nor, for my part, do I think that such instincts
should be ignored... that they exist is certain; that they modify the
indifferent impartiality of pure empiricism can hardly be denied."
("Report of the 74th Meeting of the British Association" (Presidential
Address, Cambridge 1904), page 9, London, 1905.)

When Dalton's atomic theory had been in existence some half century, it
was noted that