7-4 SCIENCE IN THE LAST HALF CENTURY. 



the relation may be expressed in another way. In each section oi the 

 series, the atomic weight is greater than in the preceding section, so 

 that if 10 is the atomic weight of any element in the first segment, 

 ic -f x will represent the atomic weight of any element in the next, 

 and w + X -\- y the atomic weight of any element in the next, and so on. 

 Therefore the sections may be represented as parallel series, the cor- 

 responding terms of which have analogous properties; each successive 

 series starting with a body the atomic weight of which is greater than 

 that of any in the preceding series, in the following fashion: 



d J> d 



c G y 



b B /3 



a A a 



to w + X tc + X -\- y 



This is a conception with which biologists are very familiar, animal 

 and plant groups constantly appearing as series of parallel modifica- 

 tions of similar and yet different primary forms. In the living world, 

 facts of this kind are now understood lO mean evolution from a com- 

 mon prototype. It is diilicult 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 un- 

 differentiated form of matter ? Fifty years ago such a suggestion 

 would have been scouted as a revival of fhe dreams of the alchemists. 

 At present it may be said to be the burning question of physico-chemi- 

 cal 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 

 jT^ther to be a uniform substance, and that the "elementary" units are, 

 broadly speaking, permanent whirlpools, or vortices, of this aither, the 

 properties of which depend on their actual and potential modes of 

 motion. It is curious and highly interesting to remark that this hy- 

 pothesis reminds us not only of the speculations of Descartes, butof those 

 of Aristotle. The resemblance of the "vortex-rings" to the "tour- 

 billons" of Descartes is little more than nominal; but the correspond- 

 ence between the modern and the ancient notion of a distinction be- 

 tween primary and derivative matter is, to a certain extent, real. For 

 this iethcrial "Ur8toff"of the modern, corresponds very closely with 

 the -fjcorrj u^rj of Aristotlc, the materia prima of his media3val follow- 

 ers; while inatter, differentiated into our elements, is the equivalent 

 of the first stage of progress towards the ifrx^^^v '^^^j or finished mat- 

 ter, of the ancient philosophy. 



If the material units of the existing order of nature are specialized 

 portions of a relatively homogeneous materia 2)rima — which were orig- 

 inated under conditions that have long ceased to exist and which remain 

 unchanged and unchangeable under all conditions, whether natural or 



