40 THE FITNESS OF THE ENVIRONMENT 



theory of the solar system. Finally, ever 

 more accurate observations and the marvel- 

 ous fertility of spectroscopical investigations 

 have brought the stars within our reach. 



The whole universe now appears to be not 

 unlike our part of it, both chemically and 

 physically. The same forms of matter, the 

 same material aggregates, the same manifes- 

 tations of energy, and similar movements are 

 everywhere present. The stars are no longer 

 changeless, but violently active bodies ; they 

 are no longer permanent, but evolving sys- 

 tems ; they are born, they grow, age, and 

 die; and throughout their evolution they 

 obey laws, which, though as yet imperfectly 

 known, appear to be common to all. Mean- 

 time the study of nebulae, comets, and meteor- 

 ites has kept pace with other departments of 

 the science, and our interpretation of the re- 

 sults of stellar astronomy * constantly gains 

 from ever increasing knowledge of the physical 

 and chemical processes in the sun. 



The universe which thus gradually has been 

 revealed to the astronomer is made up of a 

 relatively small number of types of material 



1 A description of such facts from the physico-chemical 

 point of view may be found in Arrhenius's "Lehrbuch der 

 kosmichen Physik." Leipzig, 1903. A brief popular account 

 of some of the facts in the same author's "Worlds in the Mak- 

 ing," translated by Boms. New York and London, 1908. 



