THE ETHER OF SPACE AND THE 

 PRINCIPLE OF RELATIVITY 



By SIR OLIVER LODGE, F.R.S. 



Is space filled with a continuous medium or is it occupied only 

 by segregated masses of matter ? 



Does continuity reign supreme or is discontinuity the 

 fundamental fact of the physical universe ? 



These and like questions, in many different forms, have 

 been asked throughout human history, yet no fixed and 

 universally accepted answers have been given. 



To Newton, to Huyghens, to Young — yes, to Faraday 

 also and Clerk Maxwell — the existence of a universally con- 

 necting continuous medium was more than a working 

 hypothesis ; it seemed to be a necessary conception ingrained 

 in the texture of their minds. To them pre-eminently, physical 

 action at a distance, in the technical sense, was unthinkable. 



But it has not been so with all great minds. To some — 

 to Lord Kelvin for instance, not to mention the living — it 

 appeared to be merely a question of evidence ; the fact of 

 inconceivability, if it were a fact, was not regarded as an 

 invincible barrier to the truth of a given proposition. 



To these physicists, apparently, cohesion seemed a variety 

 of gravitation and gravitation might extend across empty 

 space. Atoms need not be joined up by any intervening 

 medium ; there may be absolute void between them and yet 

 they might still gravitate and cohere. 



But how can they radiate ? how can the quiver of one excite 

 corresponding tremor in another? By bombardment of cor- 

 puscles it could be done — by some form of return to the 

 corpuscular theory of light. Periodic, truly, such bombard- 

 ment must be; "fits of easy reflection and transmission" are 

 wanted, for periodic in space and time radiation certainly 

 is ; but the term " wave " may be too pictorial — it is easy to 

 write down equations for undulatory light without conceiving 

 any continuous etherial medium in which the waves exist. 



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