2 COSMOS. 



seemed especially requisite where, in addition to the dynamic 

 action of moving forces, the powerful influence of a specific 

 difference of matter manifests itself in the terrestrial por- 

 tion of the universe. The problems presented to us in the 

 sidereal, or uranological, sphere of the Cosmos, are, consi- 

 dering their nature, in as far as they admit of being ob- 

 served, of extraordinary simplicity, and capable, by means 

 of the attractive force of matter and the quantity of its mass, 

 of being submitted to exact calculation in accordance with the 

 theory of motion. If, as I believe, we are justified in regard- 

 ing the revolving meteor-asteroids (aerolites) as portions of our 

 planetary system, their fall upon the earth constitutes the sole 

 means by which we are brought in contact with cosmical sub- 

 stances of a recognisable heterogeneity. 1 I here refer to the 

 cause which has hitherto rendered terrestrial phenomena 

 less amenable to the rules of mathematical deduction than 

 those mutually disturbing and re-adjusting movements of the 

 cosmical bodies, in which the fundamental force of homo- 

 geneous matter is alone manifested. 



I have endeavoured, in my delineation of the earth, to arrange 

 natural phenomena in such a manner as to indicate their causal 

 connexion. In describing our terrestrial sphere, I have consi- 

 dered its form, mean density, electro-magnetic currents, the 

 processes of polar light, and the gradations according to which 

 heat increases with the increase of depth. The reaction of 

 the planet's interior on its outer crust implies the existence of 

 volcanic activity ; of more or less contracted circles of waves of 

 commotion (earthquake waves), and their effects, which are not 

 always purely dynamic; and of the eruptions of gas, of mud, 

 and of thermal springs. The upheaval of fire-erupting moun- 

 tains must be regarded as the highest demonstration of the 

 inner terrestrial forces. We have therefore depicted volcanoes, 

 both central and chain formations, as generative no less than as 



1 Cosmos, vol. i. pp. 45-47, 125. 



