80 HISTORY OF GEOLOGY AND PALEONTOLOGY. 



another ; the equilibrium of matter was in a highly fickle and 

 unstable condition. The denser particles of matter tended, by 

 reason of their attractive force, to unite into a central body. 

 At the impact the particles were diverted by the disturbing 

 action of the attractive and repulsive forces ; there arose 

 numerous whirls of movement crossing one another. The 

 particles in these whirls or vortices originally moved in all 

 directions, and were constantly coming into conflict with one 

 another, but finally the movements became uniform in direc- 

 tion, and the particles revolved almost in one heavenly plane, 

 and without mutual disturbance in concentric circles round the 

 sun. Within each individual ring the attraction of the particles 

 again came into play, aggregates of the denser particles attracted 

 the lighter particles in the same ring until a planetary body 

 formed, revolving round the sun along its particular path. In 

 this way the whole planetary system, including moons and 

 comets, was thought by Kant to have taken origin in order 

 according to the distance of the path of revolution from the 

 sun ; first, the planets next the sun, then those more remote 

 from the sun. 



While Kant's mechanical theory of the universe explains the 

 origin of all the bodies in the solar system upon the same 

 fundamental principle, it yields no exact information regarding 

 the constitution and the temperature of the sun and the planets. 

 The nebular theory of Laplace, which was founded quite inde- 

 pendently of Kant, goes further in this respect, and has therefore 

 come into closer relationship with geology. 



Laplace shows that all the planets in the solar system move 

 round the sun from west to east in almost the same plane, that 

 all moons move in similar direction round their planets, and 

 that the sun rotates, so far as is known, in the same direction 

 round its own axis. In the opinion of the great mathematician, 

 a phenomenon so remarkable cannot be mere chance, but 

 indicates some general cause or combination of causes that 

 has determined all those movements. Clearly, there was a 

 time when the planetary spaces now empty were uniformly 

 filled with matter at a high temperature, representing the sub- 

 stances of the planets and moons in the finest state of 

 rarefaction, and having a rotating movement from west to 

 east. A central body, the sun, massed itself in the midst of 

 this vaporous material. 



The finely divided mass behaved like a gigantic atmosphere, 



