AN EVOLVING UNIVERSE 



By Sir James Jeans 



Former Secretary of the Royal Society of London; Research Associate, Carnegie 

 Institution of Washington 



[With 5 plates] 



When we look upwards in a clear night, we see a sky spangled 

 with stars ; we can see between two and three thousand with our un- 



3iL.Y. 



Figure 1. — Diagram pho\\iiig all stars whose distances are less than 33 light- 

 years. The size of the dots indicates their relative luminosity 



aided eyes. Some appear very bright and some very faint; astro- 

 nomical investigation shows that this results in large part from their 

 being at very different distances. The stars which look brightest are 



1 Lecture delivered before Carnegie Institution of Washington, May 18, 1931. Printed 

 by permission of Carnegie Institution. All photographs of nebulae used herein were taken 

 at the Mount Wilson Observatory except as otherwise noted. 



229 



