PORTION OF THE COSMOS. ASTROGNOSY. 27 



includes Astrognosy, or the heaven of the fixed stars ; and 

 the other, our solar and planetary system. The imperfect 

 and unsatisfactory character of this nomenclature and these 

 definitions need not be again dwelt on here. Names were 

 introduced into the natural sciences before the true dif- 

 ferences and distinctions between objects were sufficiently 

 known. ( 48 ) Such questions are, however, of less importance 

 than the connection of ideas, and the order in which the 

 objects are to be treated ; whilst novelties in the names of 

 groups, and the diversion of names in frequent use from the 

 signification they have hitherto borne, are objectionable, as 

 tending to perplexity and confusion. 



a. Astrognosy (heaven of the fixed stars). 



Nothing in space is in repose ; not even what are called 

 the fixed stars, as Halley( 49 ) first attempted to shew in the 

 case of Sirius, Arcturus, and Aldebaran, and as has been 

 proved incontestably in modern times in the case of many 

 other stars. In the course of 2100 years of observation 

 (since Aristillus and Hipparchus), the bright star Arcturus 

 has altered its place, relatively to the neighbouring fainter 

 stars, as much as two and a half times the diameter of the 

 moon. Encke remarks that the star p in Cassiopea would 

 appear to have moved three and a half times, and the star 61 

 Cygni six times, the diameter of the moon from their respec- 

 tive places, if we regard the old observations as sufficiently 

 exact to justify the conclusion. Inferences based on analogies 

 support the conjecture that progressive, and probably also 

 rotatory, motion exists everywhere. The name " fixed star" 

 leads to erroneous suppositions ; whether it be taken in its 



