126 THE LIMITATIONS OF SCIENCE 



properties ascribed to this ether to find that it operated 

 equally well if it had a density indefinitely great or one 

 indefinitely small; if it were rigid or if it were col- 

 lapsible, etc. As certainly as one physicist endowed it 

 with a property, another arose who showed that just 

 the opposite property was equally efficient. Yet we 

 might still be staggering along with the conviction that 

 somehow this supposititious stuff was of use to us; at 

 least it gave us a set of words conveying some meaning. 

 But when Maxwell proved mathematically that a third 

 kind of radiant energy of an electrical type should be 

 looked for, and when Hertz demonstrated its existence, 

 no elastic solid would serve for all three kinds ; and so, 

 for a time, we were taught simultaneously the proper- 

 ties of two coexistent ethers. An elastic solid and a 

 so-called electro-magnetic ether in a single space were 

 impossible, and the former soon collapsed since it was 

 more concrete and thus more vulnerable to criticism. 

 Maxwell's idea produced a revolution in the theory 

 of physics; heat and light remained no longer a form 

 of mechanical waves but became electro-magnetic 

 waves of a special periodicity. By a progressive sub- 

 tilization we have now arrived at Sir J. Larmor's cele- 

 brated definition of a medium which will satisfy all 

 forms of radiant energy. The ether is " a plenum with 

 uniform properties throughout all extension, but per- 

 meated by intrinsic singular points, each of which 

 determines and, so to speak, locks up permanently a 



