30 Doctrine of Progression 



any other internal cause capable of producing such an effect for 

 an infinite time, than they would believe in perpetual motion, in 

 the ordinary sense of the expression. I cannot conceive, there- 

 fore, the present state of terrestrial temperature to be a permanent 

 state. Can it belong to a perpetually recurring series of changes \ 

 I would reply, that no internal cause could account for any such 

 infinite recurrence, more than for unlimited permanence of tem- 

 perature. Such infinite recurrence could only be attributed to the 

 external causes — solar and stellar radiation. If to the former, the 

 quantity of heat radiating from the sun must be subject to enormous 

 periodical changes, but still without permanent diminution ; if to the 

 latter, it might be attributed either to similar periodical changes 

 in the radiation of the stars, or more probably to a change in the 

 position of the solar system with reference to them, as I have ex- 

 plained in my paper on Terrestrial Temperature. But we shall 

 probably all agree in regarding such hypotheses as extremely un- 

 satisfactory, and utterly unfit to be made the foundation on which 

 a great speculative theory may rest. But however unsatisfactory 

 they may be, I repeat that we have no other alternative but that 

 of adopting one of them, consistent with the most fundamental 

 properties of heat, if we maintain the theory of non-progression in 

 the strict sense in which I have used the term. And, having 

 placed the theory in this point of view, I might leave it there with- 

 out venturing into those speculations which assume the properties 

 of the matter constituting the stellar universe to be the same as 

 those which characterise the matter of our planet. Views founded 

 on such assumptions ought to be advanced with diffidence, and 

 held with cautious reserve ; but if, with such reservation, we as- 

 sume the sun and the stars to have the same properties as our own 

 planet, with respect to the generation and emission of heat, we 

 must conclude that those bodies must be subject to permanent 

 changes of temperature, as well as the earth itself, from the effect 

 of radiation. In such case even solar and stellar radiation must 

 necessarily fail to preserve the earth from that permanent change of 

 temperature which would constitute essentially a state of progres- 

 sion. In fact, adopting the assumption just stated respecting the 

 nature of the sun and stars, and reasoning from all we know of the 

 properties of matter and of heat, I am unable in any manner to 

 recognise the seal and impress of eternity stamped on the physical 

 universe, regarded as subjected to those laws alone by which we 

 conceive it at present to be governed. 



The rejection of the doctrine of progression, both with respect 

 to animate beings and inanimate matter, would seem to lead almost 

 necessarily to the opinion, that the sequence of periodical changes, 

 similar to those which have happened within the period of which 

 we can trace the geological history, has been of infinite duration. 

 It would appear to involve the rejection of the notion of a begirt" 



