THE DOCTRINE OF EVOLUTION. 587 



this process has advanced much further in some places than in 

 others. The general process may be roughly described as concen- 

 tration of cosmical matter, with dissipation of heat. Along with 

 this go sundry attendant or derivative chemical changes. We find 

 gaseous nebulae ; stars ranked in different classes by their colors, 

 perhaps indicating different stages of progress toward consolida- 

 tion ; then planets, first huge ones, like Saturn and Jupiter, with 

 small density, tremendous atmospherical disturbances, and prob- 

 ably some remains of self-luminosity ; then such as Mars, Earth, 

 and Venus, with cool, vapor-laden atmospheres and conditions fa- 

 vorable to organic life ; then smaller, quickly cooled and solidified 

 globes like our barren moon ; then cosmic rubbish like the aste- 

 roids and cosmic dust like the meteors. All, of course, are losing 

 heat. Some have cooled too quickly to allow the development of 

 life upon their surfaces ; others are still too hot, but while in this 

 stage can perhaps supply radiant heat and actinism for the sup- 

 port of life upon their neighbors. Obviously the gaseous nebula, 

 being a body in an earlier stage of consolidation and containing 

 a maximum of internal motion, is to be regarded as something 

 like what suns and their planets were in a former stage of de- 

 velopment. 



Long before all these fruits of modern astronomical observa- 

 tion had been gathered, the contemplation of our sun as a consoli- 

 dating and radiating body had suggested to one of the most pro- 

 found thinkers that ever lived the famous nebular hypothesis as 

 an account of the mode of development of our planetary system. 

 The nebular hypothesis, set forth by Immanuel Kant in 1755, was 

 the first constructive work toward a definite doctrine of evolu- 

 tion. The theory was restated in 1796 by Laplace, whose line of 

 argument was very similar to Kant's. "Within recent years it has 

 received emendations and qualifications, but the fundamental con- 

 ception of the nebulous mass acquiring spheroidal shape through 

 rotation, and increasing in oblateness until at some stage in its 

 shrinkage a portion of the equatorial surface is detached as a 

 ring of fragments which ultimately coalesce into a satellite globe 

 this fundamental conception still remains as a good working hy- 

 pothesis. 



As we now look back over the illustrations here cited and they 

 are, of course, scanty enough in comparison with what might be 

 adduced it appears that about half a century ago the foremost 

 minds of the world, with whatever group of phenomena they were 

 occupied, had fallen and were more and more falling into a habit 

 of regarding things not as having originated in the shape in which 

 we now find them, but as having been slowly metamorphosed from 

 some other shape through the agency of forces similar in nature to 

 forces now at work. Whether planets, or mountains, or mollusks, 



