H. A. Bumstead — Lor entz-Fitz Gerald Hypothesis. 493 



Art. XL "VI. — Applications of the Lor entz-Fitz Ger add Hypoth- 

 esis to Dynamical and Gravitational Problems / by H. A. 

 Bumstead. 



There is at the present time a general consensus of opinion, 

 among those best qualified to judge, that the fundamental facts 

 of optics and electro-dynamics require us to assume that the 

 ether does not partake (to any sensible extent) in the motion 

 of material bodies which pass through it. The aberration of 

 light is perhaps the most conspicuous of those phenomena 

 which it has hitherto been found impossible to account for on 

 any other hypothesis without becoming involved in serious 

 difficulties.* All the phenomena in which there is relative 

 motion of the source of light with respect to the observer, or 

 of a material medium (through which light is propagated) with 

 respect to source and observer, appear to require the above 

 assumption, even those which at first seemed to lead to a con- 

 clusion somewhat different in form. Thus the experiment of 

 Fizeau. in which he compared the velocities of. light when 

 going with, and against, a stream of water, was interpreted by 

 Fresnel as indicating a certain entrainment of the ether. This 

 interpretation was based on FresnePs theory of refraction, which 

 assumed that the etherial density was increased in material 

 media ; and it is only the excess ether which must be carried 

 by the matter. On the electron theory, however (and indeed on 

 any resonance theory of dispersion and refraction) there is no 

 excess density of the ether in ponderable bodies ; and it is not 

 difficult to see that Fizeau's experiment requires a stationary 

 ether. f A result which leads to the same view has been 

 obtained in electro-dynamics by H. A. Wilson £ in measur- 

 ing the electric force produced by moving an insulator in a 

 magnetic field. All such experiments upon the effects of rela- 

 tive motion, so far as I know, give positive results which may be 

 predicted from the hypothesis of a fixed ether, and the magni- 

 tude of the effects observed is in general of the same order as 



v 

 the fraction =, where v is the relative velocity involved, and 



Y the velocity of light. 



The theory of a stagnant ether leads us, however, in a no less 

 direct manner to expect certain modifications in the phenomena 

 of light and electricity when there is no relative motion of 



* Larmor, Aether and Matter, p. 37. Lorentz, Amst. Proc, p. 443. 1899 ; 

 Abhandlungen, I, p. 454. 



f See Lorentz. Yersuch einer Theorie der Elektrischen und Optischen 

 Erscheinungen, in Bewegten Korpern, § 68. 



X Proc. Roy. Soc, lxxiii, p. 490, 1904. 



