ON THE STRUCTURE OF THE UNIVERSE 9 



of stars of different magnitudes recently made by Messrs. 

 Chapman and Melotte. The results of this count are shown in 

 the annexed table, in which the second column gives the total 

 number of stars down to the limit of magnitude (photographic) 

 in the first column. 



Table IV 



It will be seen from this table that after the 15th magnitude, 

 the ratio of the number of stars of any given magnitude to the 

 number of the next brighter magnitude is less than two. By 

 extrapolation from these results Chapman and Melotte estimate 

 that the number of stars down to a magnitude of about 22*0 is 

 half the total number of stars, which, they conclude, " is not 

 less than one hundred thousand millions, and cannot much 

 exceed twice this amount." This result is dependent upon the 

 assumption that there is no scattering nor absorption of light 

 in space ; but although there is considerable evidence that such 

 an absorption does occur, the most reliable estimates of its 

 magnitude indicate that its amount is so slight that it cannot 

 very greatly modify the general conclusion. It follows that we 

 must regard our stellar universe as finite in extent — although 

 its dimensions are so vast as to stagger the mind— and contem- 

 plate the possibility of the existence of other, and independent 

 universes, outside it. 



It has been shown above that our universe consists of a 

 central mass more or less globular in shape, and that outside 

 this lies the Milky Way, stretching out to immense distances 

 and containing a large proportion of faint stars. This has 

 suggested that the system may really be a spiral nebula, and 



1 These are extrapolations. 



