LAWS OF HEAT. THE EARTH. 79 



One of the results of the laws of heat as they 

 exist in the globe, is, that, by their action, the 

 thermal state tends to a limited condition, which, 

 once reached, remains constant and steady, as it 

 now is. The oscillations or excursions from the 

 mean condition, produced by any temporary 

 cause, are rapidly suppressed ; the deviations of 

 seasons from their usual standard produce only a 

 small and transient effect. The impression of an 

 extremely hot day upon the ground melts almost 

 immediately into the average internal heat. The 

 effect of a hot summer, in like manner, is soon 

 lost in its progress through the globe. If this 

 were otherwise, if the inequalities and oscillations 

 of heat went on, through the interior of the earth, 

 retaining the same value, or becoming larger 

 and larger, we might have the extreme heats or 

 colds of one place making their appearance at 

 another place after a long interval ; like a con- 

 flagration which creeps along a street and bursts 

 out at a point remote from its origin. 



It appears, therefore, that both the present 

 differences of climate, and the steadiness of the 

 average at each place, depend upon the form of 

 the present laws of heat, and on the arbitrary 

 magnitudes which determine the rate of conduc- 

 tion and radiation. The laws are such as to 

 secure us from increasing and destructive in- 

 equalities of heat ; the arbitrary magnitudes are 

 data to which the organic world is adjusted. 



