414 The Theory of Aether and Electrons in the 



zodiac, it should therefore be possible to determine the sun's 

 velocity relative to the aether, or at least that component of it 

 which lies in the ecliptic. 



The same principles may be applied to the discussion of 

 other astronomical phenomena. Thus the minimum of a 

 variable star of the Algol type will be retarded or accelerated 

 by an interval of time which is found by dividing the projection 

 of the radius from the sun to the earth on the direction from 

 the sun to the Algol variable by the velocity, relative to the 

 solar system, of propagation of light from the variable ; and thus 

 the latter quantity may be deduced from observations of the 

 retardation.* 



Another instance in which the time taken by light to cross 

 an orbit influences an observable quantity is afforded by the 

 astronomy of double stars. Savaryf long ago remarked that 

 when the plane of the orbit of a double star is not at right 

 angles to the line of sight, an inequality in the apparent motion 

 must be caused by the circumstance that the light from the 

 remoter star has the longer journey to make. Yvon VillarceauJ 

 showed that the effect might be represented by a constant 

 alteration of the elliptic elements of the orbit (which alteration 

 is of course beyond detection), together with a periodic 

 inequality, which may be completely specified by the following 

 statement : the apparent coordinates of one star relative to the 

 other have the values which in the absence of this effect they 

 would have at an earlier or later instant, differing from the 

 actual time by the amount 



m, - >)i z z 

 m } + m z ' c' 



where m l and m 2 denote the masses of the stars, c the velocity 

 of light, and z the actual distance of the two stars from each 



* The velocity of light was found from observations of Algol, by C. V. L. 

 Charlier, Of versigt af K. Vet.-Ak. Forhandl. xivi (1889), p. 523. 



t Conn, des Temps, 1830. 



J Additions a la Connaissance des Temps, 1878 : an improved deduction was 

 given by H. Seeliger, Sitzungsberichte d. K. Ak. zu Miinchen, xix (1889), p. 19. 



