STAR-GROUPING, STAR-DRIFT, AND STAR-MIST. 137 



Ae heavens, he counted the stars seen in the field of view. 

 Assuming that the telescope really reached the limits of the 

 sidereal system, it is clear that the number of stars seen 

 in any direction affords a means of estimating the relative 

 extension of the system in that direction, provided always 

 that the stars are really distributed throughout the system 

 with a certain approach to uniformity. Where many stars 

 are seen, there the system has its greatest extension ; where 

 few, there the limits of the system must be nearest to us. 



Sir Wm. Herschel was led by this process of star-group- 

 ing to the conclusion that the sidereal system has the figure 

 of a cloven disc. The stars visible to the naked eye lie far 

 within the limits of this disc. Stars outside the relatively 

 narrow limits of the sphere including all the visible stars, are 

 separately invisible. But where the system has its greatest 

 extension these orbs produce collectively the diffused light 

 which forms the Milky Way. 



Sir John Herschel, applying a similar series of researches 

 to the southern heavens, was led to a very similar conclusion. 

 His view of the sidereal system differs chiefly in this respect 

 from his father's, that he considered the stars within certain 

 limits of distance from the sun to be spread less richly 

 through space than those whose united lustre produces 

 the milky light of the galaxy. 



Now it is clear that if the supposition on which these 

 views are based is just, the three following results are to be 

 looked for. 



In the first place, the stars visible to the naked eye would 

 be distributed with a certain general uniformity over the 

 celestial sphere ; so that if on the contrary we find certain 

 extensive regions over which such stars are strewn much 

 more richly than over the rest of the heavens, we must 

 abandon Sir Wm. Herschel's fundamental hypothesis and all 

 the conclusions which have been based upon it 



In the second place, we ought to find no signs of the 

 aggregation of lucid stars into streams or clustering groups. 

 If we should find such associated groups, we must abandon 



