September 19, 1913] 



SCIENCE 



393 



from a distant terrestrial source may be 

 telegraphed to us, either with a wire or 

 without ; but it is the ether that conveys the 

 message in either case, so again there will 

 be compensation. Electricity, magnetism 

 and light are all effects of the ether. 



Use cohesion, then ; have a rod stretching 

 from one place to another, and measure 

 that. But cohesion is transmitted by the 

 ether too, if, as believed, it is the universal 

 binding medium. Compensation is likely; 

 compensation can, on the electrical theory 

 of matter, be predicted. 



Use some action not dependent on ether, 

 then. Very well, where shall we find it? 



To illustrate the difficulty I will quote a 

 sentence from Sir Joseph Larmor's paper 

 before the International Congress of Math- 

 ematicians at Cambridge last year: 



If it is correct to say with Maxwell that all 

 radiation is an electrodynamie phenomenon, it is 

 equally correct to say with him that all electro- 

 dynamic relations between material bodies are 

 established by the operation, on the molecules of 

 those bodies, of fields of force which are propa- 

 gated in free space as radiation and in accordance 

 with the laws of radiation, from one body to the 

 other. 



The fact is we are living in an epoch of 

 some very comprehensive generalizations. 

 The physical discovery of the twentieth 

 century, so far, is the electrical theory of 

 matter. This is the great new theory of 

 our time; it was referred to, in its philo- 

 sophical aspect, by Mr. Balfour in his 

 presidential address at Cambridge in 1904. 

 "We are too near it to be able to contem- 

 plate it properly; it has still to establish 

 itself and to develop in detail, but I antici- 

 pate that in some form or other it will 

 prove true.* 



Here is a briefest possible summary of 

 * For a general introductory account of the elec- 

 trical theory of matter my Eomanes lecture for 

 1903 (Clarendon Press), may be referred to. 



the first chapter (so to speak) of the elec- 

 trical theory of matter. 



1. Atoms of matter are composed of elec- 

 trons — of positive and negative electric 

 charges. 



2. Atoms are bound together into mole- 

 cules by chemical affinity, which is intense 

 electrical attraction at ultra-minute dis- 

 tances. 



3. Molecules are held together by cohe- 

 sion, which I for one regard as residual or 

 differential chemical affinity over molecular 

 distances. 



4. Magnetism is due to the locomotion of 

 electrons. There is no magnetism without 

 an electric current, atomic or otherwise. 

 There is no electric current without a 

 moving electron. 



5. Radiation is generated by every accel- 

 erated electron, in amount proportional to 

 the square of its acceleration ; and there is 

 no other kind of radiation, except indeed a 

 corpuscular kind; but this depends on the 

 velocity of electrons and therefore again 

 can only be generated by their acceleration. 



The theory is bound to have curious con- 

 sequences; and already it has contributed 

 to some of the uprooting and uncertainty 

 that I speak of. For, if it be true, every 

 material interaction will be electrical, i. e., 

 etherial; and hence arises our difficulty. 

 Every kind of force is transmitted by the 

 ether, and hence, so long as all our appa- 

 ratus is traveling together at one and the 

 same pace, we have no chance of detecting 

 the motion. That is the strength of the 

 principle of relativity. The changes are 

 not zero, but they cancel each other out of 

 observation. 



Many forms of statement of the famous 

 Michelson-Morley experiment are mislead- 

 ing. It is said to prove that the time taken 

 by light to go with the ether stream is the 

 same as that taken to go against or across 

 it. It does not show that. What it shows 



