AT THE EARTH'S SURFACE. 431 



may be equal to that received. And even if it were to rise 

 higher than this, still, from gradual changes in the laws of or- 

 ganised matter, or in the species of living beings, not greater 

 than what seem to have occurred in the past revolutions of the 

 globe, the existing temperature might be sufficiently compa- 

 tible with the continuance of animated existence, and with 

 an order not very different even from that which now pre- 

 vails. 



Different views have been presented of the relation of the 

 temperature of the globe to solar heat. Some have imagined, 

 that the earth is in a state of progressive refrigeration ; and 

 while it was believed that the atmosphere could convey heat 

 onwards without limitation, this conclusion might be drawn. 

 Others, from considering merely the constant communication 

 of solar heat, have drawn the opposite conclusion, that its tem- 

 perature must increase, and this indefinitely. While a more 

 probable opinion than either, founded on the apparent unifor- 

 mity of natural operations in those past periods to which any 

 records reach, is that, the temperature has always been the 

 same, or nearly the same, as that which now prevails. The 

 view which follows from the preceding observations, is differ- 

 ent from all these, and presents a more perfect arrangement. 

 The temperature of the globe must, from the mode in which 

 heat is communicated to it, rise, and at the same time, as it 

 advances, must become more equal over the whole surface. 

 And this rise has its limits ; there cannot be either unlimited 

 increase of heat, or indefinite refrigeration; but the final result 

 will be a state of permanence and uniformity, the continuance of 

 which is secured by the very circumstance, that if it is deviated 

 from, the deviation must check itself. 



No view has been presented in physical science of equal 

 grandeur with that established from astronomical observations 



3 H 2 that 



