THE MILKY WAY. 269 



stars that compose it arrived at the same time at the 

 adult period, a period which lasts for so short a time ? 

 Or do they all reach it successively, and are those that 

 we see only a small minority as compared with those 

 that are extinct or will become luminous some day? 

 But how can we reconcile this with what has been said 

 above about the absence of dark matter in any con- 

 siderable proportion ? Must we abandon one of the 

 two hypotheses, and, if so, which? I content myself 

 with noting the difficulty, without pretending to solve 

 it, and so I end with a great mark of interrogation. 

 Still, it is interesting to state problems even though 

 their solution seems very remote. 



