156 COSMOS. 



by a careful comparison of the different aspects of the heavens 

 with those stars which have been noted as fixed points, we 

 may be enabled to discover all moving celestial bodies, whose 

 change of position can scarcely, owing to the faintness of their 

 light, be noted by the unaided eye, and that we may in this 

 manner complete our knowledge of the solar system. While 

 Harding' s admirable atlas gives a perfect representation of 

 the starry heavens as far as Lalande's Histoire Celeste, on 

 which it is founded, was capable of affording such a picture 

 Bessel, in 1824, after the completion of the first main section 

 of his zones, sketched a plan for grounding on this basis a 

 more special representation of the starry firmament, his 

 object being not simply to exhibit what had been already 

 observed, but likewise to enable astronomers by the complete- 

 ness of his tables at once to recognize every new celestial 

 phenomenon. Although the star maps of the Berlin Aca- 

 demy of Sciences, sketched in accordance with Bessel's plan, 

 may not have wholly completed the first proposed cycle, 

 they have nevertheless contributed in a remarkable degree 

 to the discovery of new planets, since they have been the prin- 

 cipal if not the sole means to which, at the present time (1850), 

 we owe the recognition of seven new planetary bodies." 23 Of 

 the twenty-four maps designed to represent that portion of 

 the heavens which extends 15 on either side of the equator, 

 our Academy has already contributed sixteen. These contain, 

 as far as possible, all stars down to the 9th magnitude and 

 many of the 10th. 



The present would seem a fitting place to refer to the 

 .-average estimates which have been hazarded on the number 

 of stars throughout the whole heavens, visible to us by the 

 aid of our colossal space-penetrating telescopes. Struvc 

 assumes for Herschel's twenty-feet reflector, which was em- 



23 Encke, Gcdiichtnissrede auf Bcssel, s. 13. 



