74 Prof. D. B. Brace on Negative Results of 



greatest axes of the ellipsoidal electrons of the equivalent 

 system at rest. Otherwise the effect would be masked in 

 using natural light, since, with this type of interferometer, 

 the above components may be as low as 25 per cent, of the 

 total interfering light, as Mills has shown*. 



The remaining second order tests first proposed by 

 FitzGeraldf and developed and carried out by TroutonJ, 

 by examining the couple on a suspended condenser, gave 

 negative results, This is completely explained on the 

 assumption of a shrinkage. 



Direct experiments on the entrainment of the aether have 

 also given negative results. Thus Lodge § sent two inter- 

 fering rays in opposite directions several times around a 

 rectangle between two rotating steel disks, without being- 

 able to detect any displacement of the interference-bands. 

 He estimates that if the disks had communicated one eight- 

 hundredth part of their velocity to the aether, he would have 

 been able to detect it. 



ZehnderU, using a different method, attempted to detect 

 any dragging of the aether by a metal plug moving within a 

 cylinder whose ends were circuited together by parallel 

 branching tubes through which two interfering rays could be 

 sent in opposite directions. If the aether had moved entirely 

 with the plug, the effect w r ould have been a thousand times 

 larger than this sensibility. Fizeau's well-known experiment 

 on the entrainment of the aether, repeated by Michelson and 

 Morley ^f, showed no effect after allowing for the reaction of 

 the moving water itself upon the interfering waves. Had 

 the aether been carried along completely, the displacement 

 would have been nearly two and a half bands, instead of 

 approximately the single band actually observed, due to the 

 reaction of the water alone. We may conclude from these 

 experiments that the aether was not entrained in any way in 

 the experiments of Morley and Miller, and that their results 

 are therefore valid, although performed within an enclosure. 



Nordmeyer **, carrying out the experiment first proposed 

 by Fizeau f t on the change in intensity of a radiant due to the 

 earth's motion, found that this variation could not have been 



* Annalen, Band xiii. p. 854. 



f ' Scientific Writings,' p. 557. 



% Trouton & Noble, Roy. Soc. Trans. A. 202. p. 165 (1903). 



§ Lodge, Roy. Soc. Trans. A. 184. p. 727 (1898). 



|| Wied. Ann. Band lv. p. 65. 



^[ Amer. Journ. Sci. (3) vol. xxxi. p. 377. 

 ** Annalen, Baud xi. p. 284. 

 ft l J ogg. Ann. Band xcii. p. 052. 



