58 



SCIENCE 



[N. S. Vol. XL VII. No. 1203 



did not at first sight appear to be helped 

 very much by FitzGerald's suggestion, 

 contained in a memoir by Lodge" "that 

 the cohesive force between molecules, and, 

 therefore, the size of bodies, may be a 

 function of their direction of motion 

 through the ether; and accordingly that 

 the length and breadth of Michelson 's stone- 

 supporting block were differently affected, 

 in what happened to be, either accidentally 

 or for some unknown reason, a compensa- 

 tory manner. This seemed a rather des- 

 perate dodge; and the impression was not 

 removed until Lorentz (who had independ- 

 ently made the same suggestion) showed' 

 that just the right alteration of dimensions 

 would take place if the intermolecular 

 forces were of electrical origin. Later the 

 experimental results of Rayleigh and of 

 Brace forced him to the conclusion that the 

 electron itself must be similarly contracted, 

 and one of the consequences of his hy- 

 pothesis was brilliantly verified by Bueh- 

 erer. 



Upon one who had followed step by step 

 this slow and laborious, but highly inter 

 esting, course of development, with its con- 

 stant action and reaction of theory and ex- 

 periment upon each other, the impression 

 of directness and simplicity made by Ein- 

 stein's papers of 1905 can scarcely be ex- 

 aggerated. The difficult and (at first 

 sight) irreconcilable results of experiment, 

 which the older theory had conscientiously 

 "explained," were taken by Einstein as 

 his postulates. There remained only to 

 describe the world as it appears to an ob- 

 server limited by these restrictive postu- 

 lates; this proved to be (for Einstein) an 

 apparently easy task and resulted in the 

 Lorentz equations for bodies in motion, 

 slightly improved, in that some relations 

 which Lorentz had obtained only approxi- 



iPhil. Trans. B. S., 184, p. 749 (1893). 

 7 ' ' Versueh einer Theorie, ' ' etc., § 92. 



mately were now exact. Since description 

 and not mechanism is the essence of the 

 method, it is unnecessary to postulate an 

 ether; and since an observer at rest with 

 reference to the ether would have no de- 

 tectable advantage over one who was in 

 motion, the assmnption of an ether was 

 not only useless, but actually in the way of 

 clear description. This rejection of the 

 ether has made Einstein's theory unpala- 

 table to many physicists, while others (as 

 well as many mathematicians) have been 

 so carried away with its beauty and el- 

 egance that the use of the word ether is to 

 them distinctly offensive. A simple rule, 

 however, enables one to converse peaceably 

 with either group separately; the same 

 statements and arguments may be addressed 

 to both, provided the word "observer" is 

 substituted for "ether," or vice versa. 



If we consider Einstein's theory from the 

 pragmatic point of view we cannot fail to 

 recognize that no new discoveries m elec- 

 trodynamics have resulted from its sug- 

 gestions. In this fact there appears to be 

 support for the opinion that a theory of 

 this type is not valuable as an instrument 

 of research, but finds its proper place as a 

 succinct summary of a body of knowledge 

 after that knowledge has been acquired by 

 other means. There are a number of con- 

 siderations, however, which serve as a 

 warning against this generalization, of 

 which I will mention but two. 



I would first call your attention to the 

 fact that the development of thermody- 

 namics, as based upon the two empirical 

 laws, exemplifies a method which is very 

 similar to that of Einstein; and we must 

 all recognize its enormous services in the 

 advancement of science. It has constantly 

 served as the guide in important experi- 

 mental investigations, and has predicted 

 results which could scarcely have been 

 foreseen on the basis of the more detailed 



