MOTION THROUGH ETHER 247 



unlikely ? According to the doctrine of relativity, as held by 

 a school of theorists who deny the existence of an ether, we 

 ought not to be able to say anything about it : we ought 

 not to be able to deny that we were travelling a million 

 times faster than light, except that both assertion and denial 

 would be considered meaningless. 



Of a revolving body we can assert that it is not spinning 

 very fast, we can even say at what absolute rate it is spinning, 

 because that kind of motion involves acceleration — centripetal 

 acceleration ; and no one appears to doubt that acceleration 

 can be observed. So it is possible to observe and measure 

 what may be called absolute rotation. For instance, the 

 period of rotation of the earth or of Jupiter can be deduced 

 from its shape. But then rotation of a piece of matter involves 

 relative or differential motion of its parts, and the question of 

 absolute motion does not really arise. But with pure translation, 

 we have no criterion that the speed is not infinite, save and 

 except the theoretical deduction — not accepted by relativity 

 theorists — that if a piece of matter moves in a quite isolated 

 manner and obedient to the first law of motion, then the fact 

 or the supposition that it is moving through a stagnant medium, 

 the ether, compels certain imaginable even if not readily 

 observable consequences to arise. Yet these may in due time 

 be looked for. 



It is becoming known that the Principle of Relativity is 

 acquiring merit and establishing its position by some brilliant 

 deductions made by Professor Einstein. 



One relates to the influence of a gravitational field upon 

 a ray of light. No such effect is yet known, but if it can be 

 observed, and if in amount it agrees with the calculated value, 

 it will be a splendid triumph. Exactly how much of the theory 

 will by that possible discovery really be established will then 

 have to be considered. Meanwhile we can await the result of 

 the proposed astronomical observations in May 191 9. 



The other deduction is an explanation of the outstanding 

 discrepancy between gravitational theory and observation in 

 the progression of the perihelion of the planet Mercury, its 

 amount being 43 seconds of arc per century. Now, this 

 progression is undoubtedly real, and it behoves us to consider 

 what are the physical facts upon which its supposed recent 

 explanation is really and solidly based. 



