12 Evolution 



came to the aid of the telescope, and the camera brought 

 further aid, the real nebulae were sorted out, and were 

 found to run into hundreds of thousands. Further, they 

 were found to be in every stage of evolution, from vast 

 even stretches of smoke-like matter to objects that stand 

 out like gigantic " catherine-wheels " on the inky back- 

 ground, and on to nebulae that have all but finished their 

 condensation into stars. Then we find clusters of stars 

 (like the Pleiades) that reveal on the photographic plate 

 faint wisps and patches of nebula lingering amongst 

 them, telling of the birth of the cluster aeons ago from a 

 vast cloud of gas. Finally, the stars themselves turn 

 out to be of different ages. Some are rising with titanic 

 energy from their nebula-cradles ; some are pouring the 

 fiery energy of full development over incalculable reaches 

 of space; some are sinking slowly to the blood-red that 

 tells of old age ; and some are dead, dark bodies whose 

 long life-history is over. 



This is the peculiar value of the facts of astronomy 

 for the student of evolution. All the chief stages of the 

 story are illustrated in the heavens, and can be verified 

 night after night. A close examination of even a 

 single district in the sky — say the district of Perseus 

 and Auriga — will reveal all the links in the chain of 

 astronomical evolution. The immeasurable vastness of 

 space compensates for the flow of time. Our telescope 

 sweeps across a field of at least 4,000 billion miles, and 

 none can say how much more, from horizon to horizon. 

 The past lives in that incalculable present. The hundred 

 million inhabitants of our stellar universe exhibit to us 

 the phases through which the star passes from the faint 

 luminosity of the nebula to the solid dark extinct sun. 



Hence we quite confidently begin the story of the 

 development of our sun and its planets from a nebula. 

 The M nebular hypothesis/' as it is still called, is an 



