1 6 DeWitt B. Brace. 



Thus the variation in intensity with distance becomes 



— ^= , approxmiately, (20) 



y- y- 



when y is taken as the dimension of the visible universe. 

 In order that the effect of absorption might equal that due 

 to the variation in distance, we should have to take a distance 

 ny, such that 



{nyy 

 or (21) 



(.9)-' = 



if the diminution in amplitude from absorption were ten per 

 cent for a distance j. Thus n would have to be very great, 

 and the system would be of dimensions n times as great as 

 those of our own stellar system. To a close approximation, 

 the system should have the same appearance whether absorp- 

 tion were present or not. The apparent finiteness of the 

 stellar universe cannot thus be due to absorption, as Struve 

 supposed, his assumption of uniform distribution requiring a 

 loss of as much as one-third the light of stars of the ninth 

 magnitude. 



Either, then, the universe must be finite, or, if infinite in 

 extent, the average density of distribution of self-luminous 

 bodies outside our own system must be exceedingly small, as 

 otherwise the sky would appear of a uniform brightness, 

 approximating that of the sun. 



16 



