178 SPECIAL EESULTS IN THE URANOLOGICAL PORTION 



V. 



PROPER MOTION OF THE FIXED STARS. PROBLEMATICAL 



EXISTENCE OF DARK BODIES. PARALLAX. MEASURED 



DISTANCE OF SOME FIXED STARS. DOUBTS CONCERNING 



THE ASSUMPTION OF A CENTRAL BODY FOR THE WHOLE 

 SIDEREAL HEAVENS. 



BESIDES variations of luminous intensity, the heaven of the 

 fixed Stars, in contradiction to its name, also undergoes 

 variation from the perpetually progressive motion of the 

 several stars. It has already been recalled how, without 

 the general equilibrium of the sidereal system being dis- 

 turbed thereby, no point in the entire heavens has remained 

 fixed, how, of the bright stars observed by the most 

 ancient of the Greek astronomers, none has maintained its 

 position in space unaltered. In two thousand years, the 

 change of place, by the accumulated effects of annual proper 

 motion, has amounted in Arcturus, /j. Cassiopeise, arid a 

 double star in Cygnus to spaces corresponding to 2, 3J, 

 and 6 diameters of the moon. At the end of three 

 thousand years, about 20 fixed stars will have altered their 

 place 1 arid upwards. ( e9 ) As the proper motions of fixed 

 stars which have been measured vary from ^th or '05 of a 

 second to 7 '7 seconds, (differing, therefore, at least in the 



