116 COSMOS. 



I can not, I think, make mc^e honorable mention of the 

 great work of the star maps of the Berlin Academy than by 

 quoting the words used by Encke in reference to this un- 

 dertaking, in his oration to the memory of Bessel : " With 

 the completeness of catalogues is connected the hope that, 

 by a careful comparison of the different aspects of the heav- 

 ens 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 faint- 

 ness of their light, be noted by the unaided eye, and that 

 we may in this manner complete our knowledge of the so- 

 lar system. While Harding's admirable atlas gives a per- 

 fect representation of the starry heavens as far as Lalande's 

 Histoire Celeste, on which it is founded, was capable of af- 

 fording such a picture Bessel, in 1824, after the comple- 

 tion 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 as- 

 tronomers, by the completeness of his tables, at once to rec- 

 ognize every new celestial phenomenon. Although the star 

 maps of the Berlin Academy of Sciences, sketched in ac- 

 cordance 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 principal, if not the sole means, to which, 

 at the present time (1850), we owe the recognition of seven 

 new planetary bodies."* 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 con- 

 tributed sixteen. These contain, as far as possible, all stars 

 down to the ninth magnitude, and many of the tenth. 



The present would seem a fitting place to refer to the 

 average estimates which have been hazarded on the num- 

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

 the aid of our colossal space-penetrating telescopes. Struve 

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

 ployed in making the celebrated star-gauges or sweeps, that 

 a magnifying power of 180 would give D.bOO.000 for the 

 number of stars lying within the zones extending 30 on ei- 

 ther side of the equator, and 20,374,000 for the wUoie heav- 

 ens. Sir William Herschel conjectured that eighteen fuill- 



* Encke, Gedachtnissrede auf Bessel, s. 13. 



