] 16 ==^TERRESTRIAL PHENOMENA. 



physical philosopher, engaged in tracing a general picture of 

 nature, from noticing the connection and co-extensive domi- 

 nion of similar forces. A minute fraction of the Earth's 

 heat belongs to the part of space through which our pla- 

 netary system is moving, the temperature of which is 

 supposed to be nearly equal to the mean temperature of the 

 poles of the Earth, and is regarded by Fourier as the product 

 of calorific radiation from all the bodies of the universe. 

 Par more powerful undoubtedly are the effects of the Sun's 

 rays on the atmosphere and on the upper strata of our 

 globe, in the electric and magnetic currents occasioned by 

 his heat-producing powers ; and in the magical and beneficent 

 influence which awakens and nourishes the germs of life in 

 the organic forms on the surface of the Earth, which will 

 be considered in a subsequent part of the volume. 



In now turning our attention exclusively to the telluric 

 sphere of nature, we will first consider the relative extent of 

 liquid and solid surface of the Earth ; its figure ; its mean 

 density, and the partial distribution of this density in the in- 

 terior of the planet; its temperature, and electro-magnetic 

 tension. These relations and forces will lead us to consider 

 the reaction of the interior of our globe on its exterior; 

 the special agency of subterranean heat, producing the 

 phenomena of earthquakes in districts of varying extent ; 

 the breaking forth of hot springs, and the more powerful 

 action of volcanic forces. Movements in the crust of the Earth, 

 sometimes sudden and in shocks, sometimes continuous and 

 almost imperceptible, alter in the course of centuries the 

 relative elevation of the land and sea, and the configuration 

 of the land beneath the ocean; while, at the same time, 

 communications are formed between the interior of the 



