ELECTRONS 63 



their architectural features or kinetic properties. 

 The IVater of Thales, the Infinite of Anaximander, 

 the Fire of Heraclitus were all inspired by this 

 instinctive craving to trace diversity back to unity. 

 Other schools, loo, besides the atomist schools, 

 were led by the same instinct to premise a materia 

 prima — a simple first substance, from which all 

 other substances were derived. Aristotle had his 

 TrpwTrj v\rj (raw Stuff) and his gct^ty] v\t] (finished 

 stuff). Diogenes of Apollonia had a surprisingly 

 clear grasp of a materia prima. His opinions we 

 have already quoted. Among the philosophers of 

 the Middle Ages the doctrine still survived. 

 Moses Maimonides (1135), the great Jewish 

 philosopher, gives the views of the Jewish school of 

 philosophy as follows : " Also the body of the 

 heaven, the body of the angels, the body of the 

 Divine Throne — such as it is assumed to be — the 

 body of anything creeping on the earth, and the 

 body of any plant, have one and the same substance ; 

 they only differ in the peculiarity of the accidents, 

 and in nothing else ; the substance of all things is 

 made up of equal atoms." Among the alchemists 

 the same idea of an urstoff was ever dominant. 

 Though they still clung to the Earth, Fire, Air, and 

 Water of Empedocles, yet they believed that these 

 elements had a common ancestor — 2i materia prima ^ 

 almost abstract in its character — and that substances 



