This is a conception with, which biologists are very familiar, animal and plant groups constantly appearing as series of parallel modifications of similar and yet different primary forms.  In the living world, facts of this kind are now understood to mean evolution from a common prototype.  It is difficult to imagine that in the not-living world they are devoid of significance.  Is it not possible, nay probable that they may mean the evolution of our ‘elements’ from a primary undifferentiated form of matter?  Fifty years ago, such a suggestion would have been scouted as a revival of the dreams of the alchemists.  At present, it may be said to be the burning question of physico-chemical science.

In fact, the so-called ‘vortex-ring’ hypothesis is a very serious and remarkable attempt to deal with material units from a point of view which is consistent with the doctrine of evolution.  It supposes the ether to be a uniform substance, and that the ‘elementary’ units are, broadly speaking, permanent whirlpools, or vortices, of this ether, the properties of which depend on their actual and potential modes of motion.  It is curious and highly interesting to remark that this hypothesis reminds us not only of the speculations 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