RELATIVE AND ABSOLUTE QUANTITIES 25 



the FitzGerald contraction is infinite, the metre rods 

 contract to nothing, and so it takes an infinite number 

 of them to fill up the interval from crest to crest of the 

 waves. 



My supplementary rule was in a way quite a good 

 rule; it would always give something absolute — some- 

 thing on which they would necessarily agree. Only 

 unfortunately it would not give the length or distance. 

 When we ask whether distance is absolute or relative, 

 we must not first make up our minds that it ought to 

 be absolute and then change the current significance of 

 the term to make it so. 



Nor can we altogether blame our predecessors for 

 having stupidly made the word "distance" mean some- 

 thing relative when they might have applied it to a 

 result of spatial measurement which was absolute and 

 unambiguous. The suggested supplementary rule has 

 one drawback. We often have to consider a system 

 containing a number of bodies with different motions; 

 it would be inconvenient to have to measure each body 

 with apparatus in a different state of motion, and we 

 should get into a terrible muddle in trying to fit the 

 different measures together. Our predecessors were 

 wise in referring all distances to a single frame of space, 

 even though their expectation that such distances would 

 be absolute has not been fulfilled. 



As for the absolute quantity given by the proposed 

 supplementary rule, we may set it alongside distances 

 relative to the earth and distances relative to Betelgeuse, 

 etc., as a quantity of some interest to study. It is called 

 "proper-distance". Perhaps you feel a relief at getting 

 hold of something absolute and would wish to follow 

 it up. Excellent. But remember this will lead you away 

 from the classical scheme of physics which has chosen 



