243 



V. 



PROPER MOTION Of THE FIXED STARS. PROBLEMATICAL 



EXISTENCE OF DARK COSMICAL BODIES. PARALLAX. 



MEASURED DISTANCES OF SOME OF THE FIXED STARS. 



DOUBTS AS TO THE ASSUMPTION OF A CENTRAL BODY 



FOR THE WHOLE SIDEREAL HEAVENS. 



THE heaven of the fixed stars, in contradiction to its very 

 name, exhibits, not only changes in the intensity of light, 

 but also further variation -from the perpetual motion of the 

 individual stars. Allusion has already been made to the 

 fact that, without disturbing the equilibrium of the star- 

 systems, no fixed point is to be found in the whole heavens, 

 and that of all the bright stars observed by the earliest of the 

 Greek astronomers, not one has kept its place unchanged. In 

 the case of Arcturus, of p Cassiopeia, and of a double star in 

 Cygnus, this change of position has, by the accumulation 

 of their annual proper motion during 2000 years, amounted 

 respectively to 2^, 3J, and 6 moon's diameters. In the 

 course of 3000 years about twenty fixed stars will have 

 changed their places by 1 and upwards. 1 Since the proper 

 motions of the fixed stars rise from -^th of a second to 

 7' 7 seconds (and consequently differ, at the least, in the 

 ratio of 1: 154), the relative distances also of the fixed stars 



1 Encke, Betrachtungen uber die Anordnung des Stern- 

 systems^ s. 12. Vide supra, p. 30. Madler, Astr., s. 445. 



