OF THE COSMOS. PROPER MOTION OF STARS. 179 



proportion of ] : 154), it follows that the relative distances 

 of the fixed stars, inter se, and the configuration of the con- 

 stellations does not remain the same for long periods. The 

 Southern Cross will not always shine in the heavens in the 

 same form which that constellation now presents, as the four 

 stars of which it is composed move with unequal velocities 

 in different paths. How many thousand years may be re- 

 quired for the entire dissolution of the constellation is not 

 to be calculated. In relations of space and time, there is 

 no absolute great or small. If we would embrace in a 

 general view the changes which take place in the heavens, 

 modifying in the course of ages the " physionomic character" 

 of the celestial canopy, or the aspect of the firmament as 

 seen at a determinate point of the earth's surface, we must 

 enumerate, as efficient causes of such alteration, (1) the 

 precession of the equinoxes and the nutation of the earth's 

 axis, by the joint influence of which new stars arise above 

 the horizon, and others become invisible ; (2) the periodic 

 and non-periodic variations of luminous intensity in many 

 fixed stars \ (3) the shining forth of new stars, some few 

 of which have remained ; (4) the revolution of telescopic 

 double stars round a common centre of gravity. Amongst 

 these so-called fixed stars, which vary slowly and unequally 

 in intensity of light and in position, 20 planets, and 20 

 satellites belonging to five of these planets, complete their 

 more rapid course. Thus, besides the countless hosts of 

 (also, without doubt, revolving) fixed stars, there are dis- 

 covered up to the present time (October 1850), 40 planetary 

 bodies. In the time of Copernicus, and of the great improver 

 of the art of observation, Tycho Brahe, only 7 were known. 

 We might also have named here as planetary bodies almost 



