46 LIGHT SCIENCE FOR LEISURE HOURS. 



was turned directly upon them they vanished, insomuch 

 that, he says, ' the idea of illusion has repeatedly arisen 

 subsequently,' yet when he came to map down the 

 places where these phantom star-streams had been 

 detected, he found that they formed regular branches 

 of the galactic system. 



Now these outlying star-streams prove first of all 

 that the star-system is not disc-shaped, but spiral in 

 figure. Between the stars which form the ordinary 

 streams of the Milky Way, and those which form the 

 phantom streams, there must lie regions in which stars 

 are either altogether wanting or strewn with much 

 less profusion than in either the nearer or the farther 

 stream. 



But this is not the only nor the chief conclusion 

 which may be drawn from the existence of the almost 

 evanescent star-streams. According to Herschel's views 

 the stars which compose those streams are only faint 

 through enormity of distance. They may be as large 

 as our sun, many of them perhaps far larger. And 

 between them there may yawn distances as large as 

 those which separate us from Arcturus or Aldebaran. 

 Now, this being so the outlying parts of our own 

 sidereal system being removed so far from us as to be 

 all but evanescent in Herschel's splendid reflector 

 how much greater ought to be the faintness of the 

 sidereal systems which lie outside ours ! If the nebulae 

 are really such systems, and made up of suns like our 

 own, then not only ought Herschel's great reflector to 

 fail in rendering them visible, but even Lord Eosse's 



