CHAPTER XI 



NEBULA 



Of late years the nebulae have been studied with 

 particular care ; and though their dynamics are not 

 yet fully understood, and though, as we have said, 

 no nebular hypothesis is quite satisfactory and 

 consistent, yet " there is good reason to believe 

 that they are really the material out of which stars 

 are made, and that in their forms, aggregations, 

 and condensations we can trace the very process 

 of evolution of stars and suns." 



Nebulae are nearly all invisible to the naked 

 eye. Seen through the telescope, they appear like 

 faint luminous clouds, but, unlike clouds, they do 

 not change their shape, and they are many millions 

 of miles away, and of tremendous size. The 

 smallest nebulae we know are much larger than the 

 sun, while some of the largest are so huge as to 

 stagger imagination. " The earth," says Sir Robert 

 Ball, " sweeps around the sun in a mighty path, 

 whose diameter is not less than 185,400,000 miles. 



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