30 RELATIVITY 



seek a new way of unravelling the complexity of natural 

 phenomena. 



Velocity through the Aether. The theory of relativity is 

 evidently bound up with the impossibility of detecting 

 absolute velocity; if in our quarrel with the nebular 

 physicists one of us had been able to claim to be 

 absolutely at rest, that would be sufficient reason for 

 preferring the corresponding frame. This has some- 

 thing in common with the well-known philosophic belief 

 that motion must necessarily be relative. Motion is 

 change of position relative to something-, if we try to 

 think of change of position relative to nothing the whole 

 conception fades away. But this does not completely 

 settle the physical problem. In physics we should not 

 be quite so scrupulous as to the use of the word absolute. 

 Motion with respect to aether or to any universally sig- 

 nificant frame would be called absolute. 



No aethereal frame has been found. We can only 

 discover motion relative to the material landmarks 

 scattered casually about the world; motion with respect 

 to the universal ocean of aether eludes us. We say, 

 "Let V be the velocity of a body through the aether", 

 and form the various electromagnetic equations in which 

 V is scattered liberally. Then we insert the observed 

 values, and try to eliminate everything that is unknown 

 except V. The solution goes on famously; but just as 

 we have got rid of the other unknowns, behold! V dis- 

 appears as well, and we are left with the indisputable 

 but irritating conclusion — 



This is a favourite device that mathematical equations 

 resort to, when we propound stupid questions. If we 

 tried to find the latitude and longitude of a point north- 



