with respect to Inanimate Matter. 29 



by either paroxysmal or gradual and uniform action of the forces 

 which have modified the earth's surface. By non-progression I 

 understand, not the absence of periodically recurring changes, but 

 of that permanent change above mentioned. The periodical changes 

 in this case, equally with the permanent changes of the former 

 case, may have been produced or accompanied by either paroxys- 

 mal or uniform action. The theory of non-progression is essen- 

 tially different from the theory of uniformity ; and thus while we 

 might allow the justice of the appeal to the Alps, made by my 

 distinguished predecessor in this chair, in proof of non-progression 

 as indicated by an apparent equality of intensity in the more recent 

 and the more remote geological action, we might reject the appeal 

 if made to prove that the forces which elevated the Alps were of 

 no greater intensity than those which have been in action during 

 the historic period. 



It is not then, I conceive, to the phenomena of elevation, or of 

 denudation and deposition, as indicating more or less of paroxys- 

 mal or tranquil action, that we must look for any demonstrative 

 evidence to decide the question before us. But there is one most 

 important agent which has doubtless been most active, not only in 

 producing the phenomena of elevation, but also in modifying the 

 characters of the inorganic matter composing the crust of the globe, 

 and it is extremely difficult to conceive how the activity of that 

 agent can have consisted with non-progression. The agent I speak 

 of is heat. I assume the truth of the simple proposition, that if 

 a mass of matter, such, for instance, as the earth with its waters 

 and its atmosphere, be placed in space of which the temperature is 

 lower than its own, it will necessarily lose a portion of its heat by 

 radiation, until its temperature ultimately approximates to that of 

 the circumambient space, unless this reduction of temperature be 

 prevented by the continued generation of heat. If there be any 

 propositions in experimental science which may be deemed incon- 

 trovertible, this, I conceive, is one of them. Now we know that 

 the interior temperature of the earth is higher than that of its 

 surface ; and, in order that this state of terrestrial temperature 

 may be consistent with non-progression, it must either be a per- 

 manent one, or must belong to a series of changes recurring perio- 

 dically, but producing no permanent change or progression from 

 a higher primitive to a lower ultimate temperature. If the present 

 temperature be permanent, it must be maintained by some cause 

 constantly acting within the earth, and generating a quantity of 

 heat exactly equal to that which is lost by radiation into surround- 

 ing space. No external cause, such as solar or stellar radiation, 

 could produce an absolutely constant, stationary temperature, 

 which should increase in descending beneath the earth's surface. 

 Chemical action might produce this effect, possibly, for a finite 

 time, but philosophers, I imagine, would no more believe that or 



