18 Temfperature of the Terrestrial Globe. 



and heat from innumerable stars, in the midst of which is placed the 

 solar system. These are three general causes which determine the 

 temperature of the earth. The third, that is, the influence of the 

 stars, is equivalent to the presence of an immense hollow sphere, 

 with the earth in the center, the constant temperature of which 

 should be a little below what would be observed in the polar regions. 



We might, doubtless, suppose radiating heat to possess properties 

 hitherto unknown, which might, in some way, take the place of this 

 fundamental temperature, which we attribute to space. But in the 

 present state of physical science, all known facts are naturally ex- 

 plained without having recourse to other properties than those deri- 

 ved from actual observation. It is sufficient t^ represent the plane- 

 tary bodies as occupying a space, the temperature of which is 

 constant. We have endeavored, therefore, to ascertain what this 

 temperature ought to be, in order that the effects on the thermome- 

 ter should be what we now observe. Now they would be entirely 

 different if we were to admit an absolute cold in space: but if we 

 progressively increase the common temperature of the girdle or hol- 

 low sphere which encloses this space, we should see effects produced 

 similar to what we now witness. We can, therefore, affirm, that the 

 actual phenomena are such as would be produced if radiation from 

 the stars was giving this temperature to all points of the planetary 

 space. The primitive internal heat which is not yet dissipated, pro- 

 duces now but a very slight effect upon the surface of the earth : it 

 manifests itself by an increase of temperature at great depths. At 

 still greater distances from the surface it may exceed the highest 

 temperatures which have ever been measured. 



The effect of the solar rays is periodical in the superficial strata 

 of the terrestrial crust. It is fixed in all points of great depths. 

 This fixed temperature of the internal parts is not the same for all 

 points. It depends principally upon the latitude of the place. 



The solar heat has accumulated in the interior of the globe, the 

 state of which has become unchangeable. That which penetrates 

 in the equatorial regions is exactly balanced by that which escapes 

 at the parts around the poles. Thus the earth gives out to celestial 

 space all the heat which it receives from the sun, and adds a part of 

 what is peculiar to itself. 



All the terrestrial effects of solar heat are modified by the inter- 

 position of the atmosphere and the presence of water. The great 

 motions of these fluids render the distribution more uniform. The 



