16 Temperature of the Terrestrial Globe. 



years must elapse before it would be reduced to half its present 

 value. 



Respecting the excess of temperature at the surface, it varies ac- 

 cording to the same law. The quantity by which it diminishes each 

 century, is equal to the present value divided by double the number 

 of centuries which have elapsed since the cooling process commen- 

 ced : and since the limit of this number is given by historical monu- 

 ments, we conclude that, from the Greek school at Alexandria, till 

 the present time, the temperature of the surface has not diminished, 

 on this account, the three hundredth part of a degree, (6lo° Fah- 

 renheit.) Here again we find that stability which the great phe- 

 nomena of the universe every where present. This stability, fur- 

 thermore, is a necessary result, and independent of the primitive 

 state, since the present excess of temperature is extremely small, 

 and will diminish for an infinite length of time. 



The effect of the primitive heat which our globe still preserves, 

 has become nearly insensible at the surface of the crust ; but it be- 

 comes more sensible at accessible depths, since the temperature 

 augments with the distance from the surface. This augmentation, 

 considered by unity of measure, would not have the same value for 

 depths very much greater. It diminishes with this depth ; but the 

 same theory shows that the excess of temperature, which is almost 

 nothing at the surface, can become enormous at a distance of some 

 thousands of metres, so that the heat of the intermediate strata would 

 exceed by far that of substances heated to whiteness. 



The course of centuries will produce great changes in these in- 

 ternal temperatures ; but at the surface these changes are at an end, 

 and the continual loss of internal heat cannot hereafter occasion any 

 cooling of climate. 



It is important to remark, that the mean temperature of any place 

 may undergo, from other accessory causes, variations more sensible 

 by far than those which are produced by the continued cooling of 

 the globe. 



The establishment and progress of human society, and the action 

 of natural powers, may, in extensive regions, produce remarkable 

 changes in the state of the surface, the distribution of the waters, 

 and the great movements of the air. Such effects, in the course of 

 some centuries, must produce variations in the mean temperature for 

 such places ; for the analytical expressions contain coefficients which 

 are related to the state of the surface, and have a great influence on 

 the temperature. 



