124 SCIENCE AND IMMORTALITY 



Let us imagine a sphere so mighty that the circle 

 would form just a girdle round its equator, and 

 let this gigantic globe be the measure wherewith 

 to compare the bulk of the vast nebula of Orion. 

 It can be demonstrated that a million of these 

 mighty globes rolled into one would not equal the 

 great nebula in bulk, though how much greater 

 than this the nebula may really be we have no 

 means of ascertaining." And yet such a nebula is 

 little more than a shred of the great nebular 

 system of the Milky Way, from which probably 

 it sprung. 



Some of the nebulae consist entirely of gases ; 

 others seem to consist entirely of clusters of minute 

 stellar points ; others, again, of gases and stars. 

 The spectrum of a gaseous nebula is composed 

 of seven bright lines : three of these indicate 

 hydrogen ; the other four lines correspond with 

 no gas we yet know. The spectrum of a stellar 

 nebula is the ordinary continuous band of colour 

 crossed with dark lines, and such a nebula, accord- 

 ingly, is often known as white nebula. There are 

 scores of gaseous nebulae, but the white number 

 tens of thousands. 



It is generally thought that the gaseous nebulae 

 are the earlier stages of the white, and that the 

 general tendency of nebulae is to end in star- 

 clusters ; but this is not certain, and the relation- 



