I 



THE MECHANISM OF NATURE 297 



Otherwise than by their effects, that is to say, the motions; which 

 motions, only, and not the forces, are indeed in the bodies. 

 Bodies are moved to and from each other, and this is performed 

 according to different laws. The natural or mechanical philoso- 

 pher endeavors to discover these laws by experiment and reason- 

 ing. But what is said of forces residing in bodies, whether 

 attracting or repelling, is to be regarded only as a mathematical 

 hypothesis, and not as anything really residing in nature." ^ 



Of Newton's laws, we are told in the "Encyclopaedia Britannica," 

 article Mechanics^ "These laws are to be considered as deductions 

 from observation and experiment, and in no sense as having any 

 a priori foundation." 



Jevons tells us (" Principles of Science," p. 739): "I demur to 

 the assumption that there is any necessary truth even in such 

 fundamental laws of nature as the Indestructibility of Matter, the 

 Conservation of Energy, or the Laws of Motion. With the 

 statement of every law we ought properly to join an estimate of 

 the number of instances in which it has been observed to hold 

 good, and the probability {i.e. the reasonableness of the expecta- 

 tion] thence calculated, that it will hold true in the next case. 

 No finite number of instances can warrant us in expecting with 

 certainty that the next event will be of like nature." 



Many who admit that since our knowledge of matter and 

 motion is based on observation and experiment it has no more 

 value than experience gives, hold, nevertheless, that there are 

 certain necessary truths or axioms ; although the word axiom does 

 not by derivation mean a necessary truth, but one that is worthy 

 of confidence. So far as nature is believed to give evidence of a 

 necessary law of causation, this opinion may be properly consid- 

 ered here, and we must ask what we mean by the assertion that 

 this law is necessary. Philosophers may, if they see fit, define 

 cause as "that which produceth a thing and maketh it to be what 

 it is " ; but it is one thing to define a word, and quite another 

 to find in nature any corresponding reality. The discovery of a 

 definition of "Mermaid" in the dictionary is no evidence that mer- 

 maids exist in nature; although it may be evidence that they 



i«Siris," 234. 



