ROMANCK OR SCIENCE? HEYL 287 



supposed entities. Ikit within this chaos there was working the 

 leaven of a principle stated by Newton in his '' Principia " as the first 

 of four " Rules of Reasoning in Philosophy ": "We are to admit no 

 more causes of natural things, than such as are both true and suffi- 

 cient to explain their appearances. To this purpose the philoso- 

 phers say, that Nature does nothing in vain, and more is in vain, 

 when less will serve; for Nature is pleasM witli simplicity, and affects 

 not the pomp of superfluous causes." 



In this Newton was but repeating a rule of philosophy laid down 

 3 centuries earlier by one of the medieval schoolmen, William of 

 Occam : " Essentials are not to be multiplied beyond necessity." 

 This in its Latin form was a famous saying in the Middle Ages, and 

 was known as " Occam's razor." In modern parlance it would prob- 

 ably be called a pruning knife. In obedience to this principle the 

 nineteenth century reduced these six essentials to three, and the 

 twentieth century went still further. 



It is to be noticed that all the fundamental concepts of eighteenth 

 century physics were regarded as material, whether they were weigh- 

 able or not. The nineteenth century retained the concept of ordinary 

 ponderable matter but did away with the imponderables, replacing 

 them by two new concepts, distinctly immaterial in their nature — 

 energy and ether. Light now became a vibration of the ether; heat 

 was regarded, according to circumstances, either as an ethereal vibra- 

 tion like light (radiant heat), or as a mode of motion of the mole- 

 cules of matter; and according to a textbook of the period electrical 

 phenomena were to be explained either as ether stress or ether flow, 

 while magnetism Avas a matter of ether vortices. Thus at the end 

 of the nineteenth century matter had been dethroned as sole monarch 

 but had been given a place as a member of a triumvirate — matter, 

 energy, and ether — to which were entrusted all tlie affairs of the 

 universe. 



It remained only to take the final step, which was done in the 

 twentieth century. Up to this time the ai)plication of Occam's razor 

 to scientific philosoph}'^ had been universally approved as conducive 

 to economy of thought and general solidification of theory. But 

 when Einstein pointed out that the concept of matter was not an 

 independent necessity but could be merged with that of energ^^ the 

 razor began to cut deep enough to hurt. 



Einstein's argimient was a strong one, for he showed clearly, and 

 without any reference to relativity, that we must either regard mat- 

 ter as a form of energy or else disregard the experimental evidence 

 for light pressure and also abandon Newton's laws of motion. As 

 the latter alternative was more painful than the first, physical 

 theory accepted the new cut of Occam's razor, eliminating the tra- 

 ditional concept of matter. 



