118 Frof. E. Grant on the Prober Motions of the Stars. [May 5, 



The last four proper motions have been recently detected at the 

 Glasgow Obserratory, where a system of star observing has been pro- 

 secuted since the year 1S60. 



It must strike every one who inspects the foregoing list that the 

 proper motion of a star has no relation whatever to the apparent magni- 

 tude of the star. Thus Eigel, one of the most brilliant stars in the 

 heavens, has a proper motion of only 20" in a thousand years. On 

 the other hand, the star 1830 Groombridge, which has a proper motion 

 of 7106" in a thousand years, is a star of only the seventh magnitude. 

 The same remark obviously applies to the other stars in the list. 

 And yet one would have thought that the brighter stars, being pre- 

 sumablv nearer to us than the fainter stars, would for that reason 

 have a larger proper motion. With respect to a Centauri and 

 61 Cvffni. which we know, from the researches of astronomers on 

 their parallax, to be the two nearest stars, it turns out conformably 

 to what one might expect, that they have also large proper motions ; 

 but what are we to think of 1830 Groombridge, which, although a star 

 of only the seventh magnitude, and one which hardly indicates any 

 sensible parallax, exhibits notwithstanding the largest proper motion 

 of any star in the heavens ? These anomalies are doubtless attribu- 

 table to differences in the absolute magnitude and intrinsic splendour 

 of the stars, and fui-thermore to the fact that the proper motions as 

 revealed by the telescope are only the motions which are resolved at 

 right angles to the line of sight. 



Heretofore the proper motion of a star has been found to take 

 place constantly in the same direction, and as the angular amount of 

 proper motion is in all cases exceedingly small, the same result will 

 probably continue to manifest itself for ages to come. The mean 

 apparent diameter of the sun amounts to 194^", consequently Arcturus 

 would require nearly a thousand years to describe, in virtue of his 

 proper motion, an arc of a great circle of the celestial sphere, equal 

 to the mean apparent diameter of the sun. 



The lecturer next adverted to the interesting spectroscopic re- 

 searches of Huggins, and Christie the present Astronomer Eoyal. on 

 the proper motions of the stars in the direction of the line of sight, 

 and he concluded with some remarks on the great problem of the 

 motion of the solar system in space. 



[E. G] 



