STELLAR ASTRONOMY 419 



A somewhat different consideration, though also not quite rigorous, 

 may help to make the character of the phenomenon still more evident. 

 The separate figures for the several areas of Fig. 3 show that the 

 symmetry line of the direct motions (calling direct the motions 

 away from the Apex) does not generally coincide with that of the 

 retrograde motions. 



The symmetry lines of the direct motions can evidently be de- 

 termined with considerable precision. It appears that they con- 

 verge very nearly to a single point of the sphere. This point is some 

 20 degrees away from the Antapex. The symmetry lines of the 

 retrograde motions cannot be determined with the same accuracy. 

 Still these too converge with some approximation towards a single 

 point, some 75 degrees away from the Apex. 



From Fig. 3 may be judged with what approximation the sym- 

 metry lines converge to the same points. The open arrowheads on 

 the side of the direct motions all point to absolutely the same point 

 of the sphere. Similarly the arrowheads on the side of the retro- 

 grade motions. These arrowheads would completely coincide with 

 the lines of symmetry if these indeed accurately intersected in one 

 point of the sphere. 



The divergence is quite small for the direct motions, and satisfac- 

 tory for the retrograde ones. 



We thus in reality have determined the Apex of the solar motion 

 separately from the stars having direct motion and from those 

 having retrograde motion. Instead of finding the same point (or 

 opposite points), we find two points lying about 125 apart. 



We will conclude that there are two sets of stars. The motion of 

 the sun relative to the mean (the centre of gravity) of the one set 

 differs from that relative to the other set. 



It follows that the one set of the stars must have a systematic 

 motion relative to the other. 



Owing to the not rigorous character of the methods, the two points 

 of convergence found in the two ways just described differ not in- 

 considerably. The mean of the two determinations gives for the 

 position of the one a point 7 degrees south of a Orionis, for the other 

 a point a couple of degrees south of y Sagittarii. We may accept 

 the directions towards these points as a first approximation for the 

 direction of the two star-streams. That they may be found to be still 

 considerably in error matters little. 



But it is important to note that the directions are only apparent 

 directions, that is, directions of the motions relative to the solar sys- 

 tem. 



If it is true that two directions of motion predominate in the 

 stellar world, then, if we refer all our motions to the centre of gravity 

 of the system, these two main directions of motion must be in reality 



