INTRODUCTION 17 



the highway but has Force in it: how else could it rot?" The 

 very idea of Force is, however, what would be termed an an- 

 thropomorphism; that is to say, it ascribes the behavior of 

 inanimate objects to causes derived from the behavior of human 

 beings. We have come to associate the motion of matter with 

 somebody or something pulling or pushing it. When one body 

 is observed to move toward another, like a stone falling to the 

 ground, it has been supposed that, although no agent is visible, 

 something must be pulling it. What, however, is actually ob- 

 served is a change of position of the body, which acquires at 

 the same time motion or velocity. The observation is correctly 

 expressed by saying that energy, before associated with the 

 position of one body with reference to another (potential energy), 

 has changed into energy of motion (kinetic energy). To suppose 

 that the one body attracts or pulls the other with a certain 

 "force" is to imagine a cause which, if it existed, would account 

 for the effect. Forces are not conserved, they have no physical 

 existence, but they still survive even in scientific parlance, mainly 

 because of the poverty of the language, which hardly allows ef- 

 fects to be expressed without some causal inference. 



An ingenious theory of gravitation was put forward a 

 century' ago which, though not accepted, is very suggestive, and 

 illustrates the difference between what science would consider a 

 real cause and one that is fictitious, like the "force of gravity." 



THE TIDES 



The only excuse for our having a tidal theory at all 

 is, of course, to connect the pertinent phenomena by 

 their causal relationships. It so happens that Newton's 

 hypothesis, for that is all it could fairly have been re- 

 garded in his day, ivas based on a single known circum- 

 stance and was conceived many decades in advance of a 

 detailed knowledge of the observational data by which 

 alone it can be established or disproved. These data 

 may now be regarded as practically complete, after many 

 decades of arduous and painstaking research, but unfor- 

 tunately for the hypothesis the result is unequivocally 

 adverse. Two of the most eminent scientists of recent 

 years, Lord Kelvin and Sir George H. Darwin, collabor- 

 ated for many years on this subject and the results of 

 their inquiries are embodied in the latter 's work, The 



