44 LIGHT SCIENCE FOR LEISURE HOURS. 



bling a cloven disc in figure. When we look along 

 the thickness of the disc we see the enormous beds of 

 stars, which lie round us in that direction as a cloud 

 of milky light, which so comes to form a cloven ring 

 round the heavens. But when we look out towards 

 the sides of the disc, where the stars are less profusely 

 scattered, we see between them the black background 

 of the sky. 



Then Herschel extended his researches to those 

 strange objects called the nebulae. He showed that 

 where astronomers had reckoned tens of these objects 

 there were in reality thousands. And he found that a 

 large proportion of the nebulae can be resolved into 

 stars. He held that these, therefore, may be looked 

 upon as external universes, resembling that great system 

 of stars of which our sun is a member. We need not, 

 at this point, dwell upon the distinction which Herschel 

 drew between nebulas of this sort, and those objects 

 which he held (and as we now know, justly) to be true 

 clouds, formed of some vaporous substance, of the 

 actual nature of which he forbore to express an opinion. 

 Let it suffice to remark that in whatever mode those 

 vaporous nebulae might be supposed to be formed, it 

 was clear to Herschel that they cannot be held to lie 

 necessarily beyond the system of the fixed stars, as he 

 held to be certainly the case with the stellar nebulae. 



Since Herschel's day a multitude of important dis- 

 coveries have been made. His son, the present Sir 

 John Herschel, carried the system of star-gaugings over 

 the southern heavens, having first trained himself for 



