446 The Doctrine of Evolution. 



of modern historical methods. Formerly the historian told 

 anecdotes or discussed particular lines of policy; now he 

 can do that as much as ever, but he can also study nation- 

 building and discern some features of the general drift of 

 events from the earliest to the most recent times. 



If we leave the earth and its inhabitants and turn our 

 attention to the starry heavens, we find plenty of subjects 

 for comparison indicating that there is a general process 

 going on, and that this process has advanced much further 

 in some places than in others. The general process may be 

 roughly described as concentration 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 consolidation ; 

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

 small density, tremendous atmospherical disturbances, and 

 probably some remains of self -luminosity ; then such as 

 Mars, Earth, and Venus, with cool, vapor-laden atmospheres 

 and conditions favorable to organic life; then smaller, 

 quickly cooled and solidified globes like our barren moon ; 

 then cosmic rubbish like the asteroids, 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 

 support 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 development. 



Long before all these fruits of modern astronomical ob- 

 servation had been gathered, the contemplation of our sun 

 as a consolidating and radiating body had suggested to one 

 of the most profound thinkers that ever lived the famous 

 nebular hypothesis as an account of the mode of develop- 

 ment of our planetary system. The nebular hypothesis, set 

 forth by Immanuel Kant in 1755, was the first" constructive 

 work toward a definite doctrine of evolution. 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 funda- 

 mental conception of the nebulous mass acquiring spheroidal 

 shape through rotation, and increasing in oblateness until at 



