344 On the Michelson-Morley jffither Experiment. 



azimuths might possibly have a neglected neutralizing influ- 

 ence ; but the wave has no such inclination, it strikes absolutely 

 plumb (I. c. p. 791). The discrepancy between this and 

 other experiments, which show definitely that the aether is 

 )wt carried along by moving bodies (Phil. Trans, vol. 189, 

 p. 149, and the Fizeau experiment also when properly inter- 

 preted, e. g. 1893, p. 751), is to be sought, I conjecture, in 

 that new and important though minute hypothetical residual 

 phenomenon first suggested by FitzGerald, and then again 

 indicated with more elaboration by H. A. Lorentz, viz. a 

 probable modification (diminution) in cohesive force due to 

 aether motion across the line of particles ; or, as Larmor ex- 

 presses it on his theory, a shrinkage in the dimension of bodies 

 along the line of their motion, of amount 1 — ^v 2 /Y 2 (Phil. 

 Trans. 1897, p. 229) ; in other words, a slight distortion in 

 the stone slab supporting Michelson's optical apparatus, exactly 

 sufficient to undo or compensate the optical influence of the 

 real (relative) aether-drift past the moving earth. 



Parenthetically I may say that the whole of this subject 

 indicates that the aether is a physical standard of rest ; and 

 that motion relative to it, which is becoming cognisable by 

 us, is in that sense an ascertained absolute motion. Every- 

 body has always had an instinctive feeling that absolute 

 motion was somehow a reality, else would there be no difference 

 between Copernicus and Ptolemy; Galileo was in some sort a 

 martyr to faith in the reality of absolute motion ; and although 

 a scientific agnostic occasionally says that we do not know 

 whether the visible system is or is not flying bodily through 

 space at a prodigious pace, he forgets that in that case every 

 electric charge would be likewise an electric current. 



Nevertheless even in that case only second- order effects of 

 those currents could be observed. They could attract or repel 

 each other, to the order of v 2 /Y 2 , but they could not deflect a 

 compass-needle, because of the compensating induced charges. 

 Any experiment made with the object of observing galvano- 

 metric action (*. e. compass-needle deflexion) in the dielectric 

 of a condenser is therefore illusory : its result is not so much 

 negative as null. It would be worth while to look for the 

 second-order electro-dynamometric effect of the earth's occa- 

 sional 28 miles a second, but it might quite possibly be com- 

 pensated by an influence to be expected on the balancing 

 elasticity. If so, these numerous compensations would be in 

 favour of an " electron " theory of matter. I see no reason, 

 however, to expect an influence on a balancing iveight. 



Yours faithfully, 



Oliver Lodge. 

 4th August, 1898. 



