MOTION THROUGH ETHER 249 



plane or a progression of the apses. And this without any 

 reference to the theory of relativity. 



To summarise briefly the result of the calculation referred 

 to : — 



If the sun's proper motion through the ether is taken as 

 about two-thirds that of the earth in its orbit and as directed 

 to an apex whose latitude or inclination to the ecliptic is about 

 6o° (somewhere near Vega), i.e. if the cosmic star group con- 

 taining the Sun is regarded as fixed, then the apse progression 

 of Mercury comes out only 2 ""4 per century ; which though not 

 hopelessly of the wrong order of magnitude is much too small. 

 But if the whole system were advancing in a certain direction, 

 viz. towards longitude 294 , with three times the earth's 

 orbital velocity, as one of Kapteyn's star-groups, then, while 

 there would be nothing excessive in the apsidal progressions of 

 other bodies in the solar system — for the components acting 

 on the earth and Venus would be small — the revolution of the 

 orbits both of Mercury and Mars would come out in accordance 

 with observation. 



