RECENT COSMOGONIES 215 



etesimal impacts upon the nucleating bodies probably 

 gave rise to the direct rotations, and, furthermore, doubt- 

 less generated such retrograde rotations as are known to 

 exist within the system. 



Doctor Chamberlin seeks to explain the recurrence 

 of ice ages in the long past, not by variations in the solar 

 temperature, but by the periodicity of terrestrial crustal 

 convulsions. For this he prepares the ground by deny- 

 ing the sufficiency of the impact hypothesis to explain any 

 part of the earth 's present internal heat, and, instead, de- 

 rives this heat partly from the bodily contraction of the 

 planet and partly from radio-activity. He argues, that 

 during periods of quiescence this internal heat accumu- 

 lates and, finally, having gained sufficient strength, forces 

 an outlet for itself, upheaving the crust into mountain 

 ranges and loading the atmosphere with immense quanti- 

 ties of carbonic dioxide. Now, carbon dioxide is an effi- 

 cient absorber of heat, hence, in the periods when the at- 

 mosphere was rich with it that is to say, during the in- 

 terims between the mountain-making cataclysms the 

 earth experienced her genial climates. On the other 

 hand, however, from the moment of the subsiding of these 

 convulsive movements, the carbon dioxide began to be 

 gradually extracted from the atmosphere, by plants to 

 form coals and other carbonaceous deposits, and by pre- 

 cipitation in the rains and subsequent absorption in the 

 rocks ; a process which eventually brought about periods 

 of low temperature immediately preceding the upheaval 

 next in order of events. But let me quote from his own 

 words (Origin of the Earth, p. 103 et seq.) : 



In the sun, there is a persistent eruptive tendency of great 

 power. At short intervals, great bolts of sun-substance are shot 

 forth at high velocities. This takes place without any obvious 

 outside stimulus; or, if there be such stimulus, it is not declared. 

 Beyond question if suitable strong stimulus from without were 

 brought to bear on the sun, such as the differential attraction of 

 a passing star, it would respond with eruptions of much greater 

 intensity and mass. 



It thus appears that from so simple a cause as the differential 

 gravity called into action by the close approach of one massive 

 body to another, there may arise a graded series of eruption^ 



