1919] on Ether and Matter 455 



But we have no sense of straightforward locomotion, and not the 

 slightest clue to either the magnitude or direction of our motion 

 through space. We can ascertain approximately how the sun is 

 moving with reference to our system or cosmos of stars, but we do 

 not know at what rate that system is itself moving. For all we know 

 it may be moving very fast : hundreds of miles per second. 



We have a sense of acceleration however ; we experience it in a 

 lift as it begins to descend ; and if the sensation is repeated often 

 enough, as on a rough sea, the result is unpleasant. We have also a 

 sense of rotation ; we can tell when our vehicle — say a Tube train — 

 turns a corner in the dark. Most animals appear to have a sense of 

 rotation, apparently located in the ear. But we have no sense of 

 direct translation; and we have so far failed to devise any 

 instrumental means for detecting our motion through the ether of 

 space. 



The failure is not for lack of trying. Many experiments have 

 been tried, but there is always some compensating efifect ; so we get 

 no answer to the question — at what rate and in what direction are we 

 moving ? The best known experiment is that of Michelson and 

 Morley, the result of which seems to assert that the ether clings to 

 the earth, or that the earth is not moving through any kind of 

 substance. But Fitzeau's classical experiment showed that a trans- 

 parent body carried with it none of the internal ether of space ; and 

 experiments made by myself * at Liverpool in the nineties of last 

 century show that a rapidly moving opaque body carries no external 

 ether with it, that there is no perceptible viscous drag or cling between 

 matter and ether, and accordingly demonstrates that stagnation or 

 absence of relative ether drift past the earth is not a reasonable 

 explanation of Michel son's negative result. 



The two experiments together, in fact, ought to be taken as 

 establisliing the reality of the most interesting of all the compensa- 

 ting effects yet discovered, viz. the FitzGerald-Lorentz contraction 

 of all matter in motion, which the electrical theory of cohesion 

 renders so extremely probable. It only amounts to a 3-inch shrinkage 

 in the whole diameter of the earth in the direciion of motion ; but it 

 is enough. This slight contraction or change of shape in moving 

 bodies I regard as the definite and interesting compensating effect in 

 this case. Incidentally, moreover, it establishes the electrical, i.e. the 

 chemical, nature of cohesion. For given that cohesion is a residual 

 chemical affinity — due to the outstanding attraction of molecules 

 composed of neutral groups of equal opposite electric charges, brought 

 so near together that the attraction between molecules is no longer 

 averaged to zerof — then, on orthodox MaxwelUan electric theory, a 



* See Phil. Trans., vol. clxxxiv. (1913), pp. 727-804, and vol. clxxxix. (1897), 

 pp. 149-166. 



t See for instance my book on Electrons, chap. xvi. 



YoL. XXII. (No. 113) 2 I 



