TERRESTRIAL PHENOMENA. 168 



ulcus rings, the same connection with this contiguous Sun, as 

 well as with all the remote suns that shine in the firmament, 

 is still revealed through the phenomena of light and radiating 

 heat. The difference in the degree of these actions must not 

 lead the physicist, in his delineation of nature, to forget the 

 connection and the common empire of similar forces in the 

 universe. A small fraction of telluric heat is derived from 

 the regions of universal space in which our planetary system 

 is moving, whose temperature (which, according to Fourier, 

 is almost equal to our mean icy polar heat) is the result of the 

 combined radiation of all the stars. The causes that more pow- 

 erfully excite the light of the Sun in the atmosphere and in the 

 upper strata of our aii that give rise to heat-engendering elec- 

 tric and magnetic currents, and awaken and genially vivify 

 the vital spark, in organic structures on the earth's surface, 

 must be reserved for the subject of our future consideration. 



As we purpose for the present to confine ourselves exclusive- 

 ly within the telluric sphere of nature, it will be expedient to 

 cast a preliminary glance over the relations in space of solids 

 and fluids, the form of the Earth, its mean density, and the 

 partial distribution of this density in the interior of our planet, 

 its temperature and its electro-magnetic tension. From the 

 consideration of these relations in space, and of the forces in- 

 herent in matter, we shall pass to the reaction of the interior 

 on the exterior of our globe ; and to the special consideration 

 of a universally distributed natural power — subterranean heat ; 

 to the phenomena of earthquakes, exhibited in unequally ex- 

 panded circles of commotion, which are not referable to the 

 action of dynamic laws alone ; to the springing forth of hot 

 wells ; and, lastly, to the more powerful actions of volcanic 

 processes. The crust of the Earth, which may scarcely have 

 been perceptibly elevated by the sudden and repeated, or al- 

 most uninterrupted shocks by which it has been moved from 

 below, undergoes, nevertheless, great changes in the course ot 

 centuries in the relations of the elevation of solid portions, 

 when compared with the surface of the liquid parts, and even 

 in the form of the bottom of the sea. In this manner si- 

 multaneous temporary or permanent fissures are opened, by 

 which the interior of the Earth is brought in contact with 

 the external atmosphere. Molten masses, rising from an un- 

 known depth, flow in narrow streams along the declivity of 

 mountains, rushing impetuously onward, or moving slowly 

 and gently, until the fiery source is quenched in the midst of 

 exhalations, and the lava becomes incrusted, as it were, by 



