154 WRITINGS OF JOSEPH HENRY. [1855- 



dred volcanoes, which occasionally emit heated materials, 

 and in some cases incandescent lava. 



Seventh. The oblate form of the earth is on an average 

 that which would be due to the rotation of a liquid mass. 



From all these facts we may now safely admit as a definite 

 theory, the hypothesis which was at first a mere antecedent 

 probability, namely, that the earth was at one time in a 

 highly heated state, and that its interior, even at the present 

 moment, is still at a very elevated temperature. If we apply 

 this hypothesis to the facts of geology as they are generalized 

 and arranged at the present day, we have a complete ex- 

 planation of the whole; or if there be any outstanding 

 phenomena not yet included in this generalization, their 

 number is so small in comparison to those included in it, 

 that they may reasonably be left for the present until further 

 discovery shall throw more light upon their character. The 

 great principle of universal gravitation was not abandoned 

 though at one time several facts in regard to the motion of 

 the moon could not be referred to it. The same considera- 

 tion applies to moral subjects as well as to those of science. 



Equilibrium of the Atmosphere. 



The aerial covering which surrounds our earth may be 

 compared to an ocean, of which the bottom is composed of 

 land and water, which has a definite surface above, probably 

 agitated by tidal waves of great extent and magnitude. 

 Although nearly eight hundred times lighter than water at 

 the surface of the earth, yet it possesses a very appreciable 

 weight, since a cubic yard of it weighs about two pounds, 

 and consequently when moving with high velocities it pro- 

 duces great mechanical effects upon bodies subjected to its 

 momentum. 



This ocean, unlike the aqueous ones belonging to our earth, 

 diminishes in density very rapidly as we ascend, and finds 

 its limit at that elevation at which the repulsion of the last 

 layer of atoms added to the centrifugal force of the earth's 

 rotation is just balanced by the attraction of gravitation. 



