1882.] Prof. B. Grant on the Proper Motions of the Stars. 115 



WEEKLY EVENING MEETING, 

 Friday, May 5, 1882. 



Warren De La Rue, Esq. M.A. D.C.L. F.R.S. Vice-President, 



in the Chair. 



Professor R. Grant, M.A. LL.D. F.R.S. 



The Proper Motions of the Stars. 



The spectacle presented by the stellar heavens as viewed by ordinary 

 observers is characterised by two remarkable features, the absence of 

 uniformity in the brightness, and the absence of uniformity in the 

 distribution of the stars. Certain of the stars soon came to be 

 recognisable by their superior lustre, and certain groups of stars 

 became familiarly known as so many landmarks in the stellar firma- 

 ment. The way was thus prepared for an important discovery. It 

 w'as ascertained respecting a limited number of the stars that their 

 places in the heavens relatively to the general multitude of the stars 

 were continually changing. They consequently received the appella- 

 tion of planets, or wandering stars, while, on the other hand, the 

 stars in general, in consequence of their always maintaining the same 

 relative position, were denominated fixed stars. Ptolemy, in his 

 great w^ork upon the astronomy of the ancients, places the earth in 

 the centre of the universe, and assumes the sun, moon, and planets to 

 be revolving in orbits around it, while beyond all was the sphere of 

 the fixed stars, which revolved with a uniform motion around the 

 earth, effecting a complete revolution once in every twenty-four 

 houi's. No opinion is expressed respecting the natui'e of the stars, 

 nor is any allusion made to the possibility of the stars being endued 

 with a proj)er motion. 



When Copernicus propounded the true system of the universe, he 

 made the earth a planet revolving like the other planets round the 

 sun, and he explained the phenomenon of the diurnal revolution of 

 the starry sphere by the revolution of the earth upon a fixed axis in 

 the opposite direction. No opinion was expressed by him respecting 

 the physical nature of the celestial bodies, or their having any pro- 

 bable community with the earth in this respect. Indeed, it could 

 hardly be said that any new light was thrown upon the physics of 

 astronomy by the theory of Copernicus. As a mathematical exposi- 

 tion of the movements of the celestial bodies it was eminently 

 successful. Indeed, it wanted only the discoveries of Kepler re- 

 specting the elliptical movements of the planets to make it perfect 

 in this respect. But it must be acknowledged that in the system 



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