The Primary Planets. 311 



year 1771. The tables of Berlin estimate them 

 at 700 ; and some have even supposed that there 

 are millions. They differ greatly in size : some 

 are so small as to appear like the fixed stars, 

 others not larger than Venus; while Hevelius 

 observed one in 1651, which was equal in ap- 

 parent magnitude to the full moon ; its light was, 

 however, much more pale and dim, and its as- 

 pect, on the whole, dismal. The nucleus of the 

 planet which appeared in the year 1807 was very 

 large; while the comet of 1811 had scarcely any 

 perceptible solid nucleus. The beautiful comet 

 of the summer of 1819 had a very evident nu- 

 cleus : its tail, also, was for a few evenings very 

 splendid. 



