DUMBER OF THE 1 TXED STA.RS. 141 



d;s nordlichen Himmels (Survey of the Northern Heavens] to 

 sibinit the previous results of Star - catalogues to a new 

 and careful examination. In the lowest class of stars visible 

 to the naked eye, much uncertainty arises from organic differ- 

 ence in individual observations ; stars between the 6th and 

 7th magnitude being frequently confounded with those strictly 

 belonging to the former class. We obtain, by numerous 

 combinations, from 5000 to 5800, as the mean number of the 

 stars throughout the whole heavens visible to the unaided eye. 

 Argelander 4 determines the distribution of the fixed stars ac- 



4 I cannot attempt to include in a note all the grounds on 

 which Argelander's views are based. It will suffice if I 

 extract the following remarks from his own letters to me : 

 "Some years since (1843,) you recommended Captain Schwink 

 to estimate from his Mappa Coelestis, the total number of stars 

 from the 1 st to the 7th magnitude inclusive, which the heavens 

 appeared to contain ; his calculations give 12148 stars for the 

 space between 30 south and 90 north declination; and conse- 

 quently, if we conjecture that the proportion of stars is the same 

 from 30 S. D. to the South Pole, we should have 16200 stars of 

 the above-named magnitudes throughout the whole firmanent. 

 This estimate seems to me to approximate very nearly to the 

 truth. It is well known, that on considering the whole mass, 

 we find each class contains about three times as many star? 

 as the one preceding. (Struve, Catalogus Sieilarwndupliciuni, 

 p. xxxiv ; Argelander, Banner Zonen, s. xxvi.) I have given 

 in my Uranometria, 1441 stars of the 6th magnitude, north of 

 the equator, whence we should obtain about 3000 for the 

 whole heavens ; this estimate does not, however include the 

 stars of the 6*7 mag., which would be reckoned among those 

 of the 6th, if only entire classes were admitted into the cal- 

 culation. I think the number of the last-named stars might 

 be assumed at 1000, according to the above rule, which would 

 give 4000 stars for the 6th, and 12000 for the 7th, or 18000 

 for the 1st to the 7th inclusive. From other considerations 

 on the number of the stars of the 7th magnitude, as given, in 

 my zones, namely 2257, (p. xxvi.) and allowing for those 

 have been twice or oftener observed, and for thosa 



