188 Mr. N. Campbell on the JEther. 



terrestrial sources are considered. Our observations prove, 

 as the consideration of the simple facts of electrostatics 

 suggested a priori, that the effective velocity in electro- 

 magnetic phenomena is the relative velocity between the 

 acting and ,; observing " systems ; the words u fixed in the 

 aether }> mean, for any given observer, " fixed in the system 

 the action of which he is observing/' Even if we start from 

 the standpoint of the " aetherialist," observation forces us to 

 accept the principle of relativity. 



§ 10. But believers in the aether refused to accept the logic 

 of their conclusions ; they were so obsessed by ideas derived 

 from their constant use of the word, that they would not 

 accept the idea that an observer could have at the same time 

 several different velocities relative to the aether. They 

 talked of " reconciling " the results of aberration and of the 

 Michelson experiment; but there was no "reconciliation" 

 needed. The results formed a perfectly logical whole without 

 any trace of contradiction. It is true that, if velocity is defined 

 as for a solid material body, a conclusion that one body has 

 several different velocities relative to another does prove that 

 there has been some fallacy in the argument ; but they had 

 defined velocity in a perfectly different way, and there was 

 no reason to suppose that the new definition of velocity 

 would have the same limitations as the old. As well might 

 a mathematician, previously acquainted only with real quan- 

 tities, who had established a system for the solution of 

 quadratic equations, think there was need for " reconciliation" 

 when first he encountered an imaginary root. 



The " reconciliation " which was effected was in truth a 

 revolution and a most disastrous revolution. The " aethe- 

 rialists" declared that they were going to throw over their 

 old definition and substitute a new one ; that this decision 

 was wise everyone will agree, but there will not be agreement 

 as to the wisdom of their new choice. It was now said that 

 the difference between the velocities relative to the aether of 

 any two bodies was equal to their relative velocity, but that 

 the velocity relative to the aether of any body was uncertain 

 to the extent of a constant. They then proceeded to show 

 with great care that no experiment which we could possibly 

 hope to perform, until our appliances attain a perfection of a 

 different order,, could give us any information as to the 

 value of that constant ; but that if such experiments ever 

 could be performed, there was no reason for supposing 

 that the quantity which was assumed to be constant would 

 actually be found to be constant. And then they settled 

 down with a sigh of satisfaction in the happy conviction 

 that a solution of all the difficulties connected with the 



