CHAPTERS ON THE STARS. 515 



From all these results it would seem that the most likely apex of the 

 solar motion is toward the point in 



Eight Ascension, 280° 

 Declination, 38° north. 



This point is situated in the constellation Lyra, about 2° from the 

 first magnitude star Vega. The uncertainty of the result is more than 

 this difference, four or five degrees at least. We may therefore state the 

 conclusion in this form: 



The apex of the solar motion is in the general direction of the constella- 

 tion Lyra, and probably very near the star Vega, the brightest of that con- 

 stellation. 



It must be admitted that the wide difference between the position 

 of the apex from large and from small proper motions, as found by 

 Porter, Boss and Stumpe, require explanation. Since the apparent 

 motions of the stars are less the greater their distance, these results, if 

 accepted as real, would lead to the conclusion that the position of the 

 solar apex derived from stars near to us was much further south than 

 when derived from more distant stars. This again would indicate that 

 our sun is one of a cluster or group of stars, having, in the general 

 average, a different proper motion from the more distant stars. But 

 this conclusion is not to be accepted as real until the subject has been 

 more exhaustively investigated. The result may depend on the selec- 

 tion of the stars; and there is, as yet, no general agreement among 

 investigators as to the best way of making the determination. 



The next question which arises is that of the velocity of the solar 

 motion. The data for this determination are more meagre and doubtful 

 than those for the direction of the motion. The most obvious and 

 direct method is to determine the parallactic motion of the stars of 

 known parallax. Eegarding any star 90° from the apex of the solar 

 motion as in a state of absolute rest, we have the obvious rule that the 

 quotient of its parallactic motion during any period, say a century, 

 divided by its parallax, gives the solar motion during that period, in 

 units of the earth's distance from the sun. In fact, by a motion of the 

 sun through one such unit, the star would have an apparent motion in 

 the opposite direction equal to its annual parallax. If the star were not 

 90° from the apex we can easily reduce its observed parallactic motion 

 by dividing it by the sign of its actual distance from the apex. 



Since every star has, presumably, a proper motion of its own, we can 

 draw no conclusion from the apparent motion of any one star, owing to 

 the impossibility of distinguishing its actual from its parallactic motion. 

 We should, therefore, base our conclusion on the mean result from a 

 great number of stars, whose average position or center of mass we 

 might assume to be at rest. Here we meet the difficulty that there are 



