PROPER MOTION OF THE STARS. 251 



Homer's observations with more recent ones." The proper 

 motion of the stars was in some degree recognized as a general 

 fact, even in the middle of the last century ; but for the more 

 precise and numerical determination of this class of pheno- 

 mena we are indebted to the great work of William Herschel 

 in 1783, founded on the observations of Flamstead, 4 and still 

 more to Bessel and Argelander's successful comparison of 

 Bradley's "Positions of the Stars for 1755" with recent 

 catalogues. 



The discovery of the proper motion of the fixed stars has 

 proved of so much the greater importance to physical astro- 

 nomy, as it has led to a knowledge of the motion of our own 

 solar system through the star-filled realms of space, and, 

 indeed, to an accurate knowledge of the direction of this 

 motion. We should never have become acquainted with this 

 fact, if the proper progressive motion of the fixed stars were 

 so small as to elude all our measurements. The zealous 

 attempts to investigate this motion, both in its quantity and 

 its direction, to determine the parallax of the fixed stars, 

 and their distances, have, by leading to the improvement and 

 perfection of arc -graduation and optical instruments in 

 connexion with micrometric appliances, contributed more 

 than anything else to raise the science of observation to the 

 height which, by the ingenious employment of great meridian- 

 circles, refractors, and heliometers, it has attained, especially 

 since the year 1 830. 



The quantity of tli2 measured proper motions of the stars 

 varies, as we intimated at the commencement of the pre- 

 sent section, from the twentielh part of a second almost to 

 eight seconds. The more luminous stars have in general 

 a slower motion than stars from the 5th to the 6th and 



* Delambre, Hist, de I'Astron. moderns, t. ii. p. 668. 

 Also in Hist, de I'Astron. au ISeme siecle, p. 448. 

 4 Philos. Transact., vol. Ixxiii. p. 138. 



