60 THE ADVANCE OF SCIENCE 



tween the modern and the ancient notion 

 of a distinction between primary and de- 

 rivative matter is, to a certain extent, 

 real. For this ethereal 'Urstoff' of the 

 modern corresponds very closely ■with, the 

 7rpcoT7) v\r) 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 eV^ax?; vXij, 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 un- 

 der all conditions, whether natural or ar- 

 tificial, 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. The- 



