265] Motion of the Sun in Space 345 



depending on the rapidity of the sun's motion and on 

 the nearness of the stars in question. The effect is exactly 

 of the same nature as that produced when, on looking 

 along a street at night, two lamps on opposite sides of the 

 street at some distance from us appear close together, but 

 as we walk down the street towards them they appear to 

 become more and more separated from one another. In 

 the figure, for example, L and L' as seen from B appear 

 farther apart than when seen from A. 



L 



FIG. 84. Illustrating the effect of the sun's motion in space. 



If the observed proper motions of stars examined are not 

 of this character, they cannot be explained as due merely to 

 the motion of the sun ; but if they shew some tendency 

 to move in this way, then the observations can be most 

 simply explained by regarding the sun as in motion, and 

 by assuming that the discrepancies between the effects 

 resulting from the assumed motion of the sun and the 

 observed proper motions are due to the motions in space 

 of the several stars. 



From the few proper motions which Mayer had at his 

 command he was, however, unable to derive any indication 

 of a motion of the sun. 



Herschel used the proper motions, published by Maskelyne 

 and Lalande, of 14 stars (13 if the double star Castor be 

 counted as only one), and with extraordinary insight detected 

 in them a certain uniformity of motion of the kind already 

 described, such as would result from a motion of the sun. 

 The point on the celestial sphere towards which the sun 

 was assumed to be moving, the apex as he called it, was 

 taken to be the point marked by the star X in the constella- 



