eculations of Descartes, but
of those of Aristotle. The resemblance of the 'vortex-rings' to the
'tourbillons' of Descartes is little more than nominal; but the
correspondence between the modern and the ancient notion of a
distinction between primary and derivative matter is, to a certain
extent, real. For this ethereal 'Urstoff' of the modern corresponds
very closely with the prhote hyle of Aristotle, the _materia prima_ of
his mediaeval followers; while matter, differentiated into our
elements, is the equivalent of the first stage of progress towards the
heschhate hyle, or finished matter, of the ancient philosophy.

If the material units of the existing order of nature are specialised
portions of a relatively homogeneous _materia prima_--which were
originated under conditions that have long ceased to exist and which
remain unchanged and unchangeable under all conditions, whether
natural or artificial, hitherto known to us--it follows that the
speculation that they may be indefinitely altered, or that new units
may be generated under conditions yet to be discovered, is perfectly
legitimate. Theoretically, at any rate, the transmutability of the
elements is a verifiable scientific hypothesis; and such inquiries as
those which have been set afoot, into the possible dissociative action
of the great heat of the sun upon our elements, are not only
legitimate, but are likely to yield results which, whether affirmative
or negative, will be of great importance. The idea that atoms are
absolutely ingenerable and immutable 'manufactured articles' stands on
the same sort of foundation as the idea that biological species are
'manufactured articles' stood thirty years ago; and the supposed
constancy of the elementary atoms, during the enormous lapse of time
measured by the existence of our universe, is of no more weight
against the possibility of change in them, in the infinity of
antecedent time, than the constancy of species in Egypt, since the
days of Rameses or Cheops, is evidence of their immutability during
all past epochs of the earth's history. It seems safe to prophesy
that the hypothesis of the evolution of the elements from a primitive
matter will, in future, play no less a part in the history of science
than the atomic hypothesis, which, to begin with, had no greater, if
so great, an empirical foundation.

[Sidenote: The old and the new atomic theory.]

It may perhaps occur to the reader that the boasted progress of