FORCE 39 



ous ether has gravity has not been answered. We 

 have no knowledge that the luminiferous ether is 

 attracted by gravity; it is sometimes called impon- 

 derable because some people vainly -imagine that it 

 has no weight. I call it matter with the same kind 

 of rigidity that this elastic jelly has."* 



"The luminiferous ether is an elastic solid for 

 which the nearest analogy I can give you is this jelly 

 which you see."t 



"Now what is the luminiferous ether? It is mat- 

 ter prodigiously less dense than air — millions and 

 millions and millions of times less dense than air. 

 We can form some sort of idea of its limitations. 

 We believe it is a real thing, with great rigidity in 

 comparison with its density; it may be made to 

 vibrate 400 million, million times per second; and yet 

 be of such density as not to produce the slightest 

 resistance to any body going through it." J 



He has also assigned to it a density which makes 

 one cubic centimeter weigh .000,000,000,000,000,- 

 000,936 grain. "This density, although about the 

 same as that of the atmosphere at the height of 340 

 kilometers, is yet enormously great as compared 

 with that which air would assume in interstellar 

 space. ' The rigidity of the ether, according to the 

 same authority, is approximately one thousand-mill- 

 ionth of that of steel ; so that masses of ordinary mat- 

 ter can pass through it readily. "§ 



Lodge speaks of it as "a perfectly continuous, sub- 

 tle, incompressible substance pervading all space and 

 penetrating between the molecules of all ordinary 

 matter which are imbedded in it and connected with 

 one another by its means. And we must regard it as 

 the one universal medium by which all actions be- 



* Popular Lectures and Addresses, by Sir W. Thomson, pp, 328, 329. 

 t Ibid, p. 327. X Ibid, 347. § Barker's Physics, p. 366. 



