CHAPTERS ON THE STARS. 389 



Here it is to be remarked that under magnitude 6 are included many 

 other than the lucid stars, namely, all down to magnitude 6.4. The 

 last column gives the entire number of stars down to each order of mag- 

 nitude. 



It will be remarked that the number of stars of each order is rather 

 more than three times that of the order next higher. How far does this 

 law extend? Argelander's 'Durchmusterung,' which is supposed to in- 

 clude all stars to magnitude 9.5, gives 315,039 stars for the northern 

 hemisphere, from which it would be inferred that the whole sky con- 

 tains 630,000 stars to the ninth magnitude. Comparing this with the 

 number 7,647 of stars to the magnitude 6.5, we see that it is forty-fold, 

 so that it would require a ratio of about 3.5 from each magnitude to the 

 next lower. But it is now found that Argelander's list contains, in the 

 greater part of the heavens, all the stars to the tenth magnitude. 



On the other hand, Thome's Cordoba 'Durchmusterung' gives 340,- 

 380 stars between the parallels —22° and —42°. This is 0.14725 of the 

 whole sky, so that, on Thome's scale of magnitude, there are about 

 2,311,000 stars to the tenth magnitude in the sky. This is more than 

 three times the Argelander number to the ninth magnitude. 



It would, therefore, seem that the ratio of number for each magni- 

 tude must exceed 3, even up to the tenth. If a ratio of only 3 extends 

 four steps farther, the whole number of stars in the sky down to mag- 

 nitude 14.5 inclusive must approach 200 millions. Until the interna- 

 tional photographic chart of the sky is subjected to a detailed examina- 

 tion, it is impossible to make an estimation with any approach to 

 certainty. 



