NATURAL HISTORY OF CREATION. 39 



sun's rays ceases. Then, however, commences a tem- 

 perature from an entirely different cause, one which 

 evidently has its source in the interior of the earth, and 

 wliich regularly increases as we descend to gi-eater and 

 greater depths, the rate of increment being about one 

 degree Fahi-enheit for every sixty feet ; and of this high 

 temperature there are other evidences, in the phenomena 

 of volcanoes and thermal springs, as well as in what is 

 ascertained with regard to the density of the entire mass 

 of the earth. This, it will be remembered, is four and a 

 half times the weight of water ; but the actual weight of 

 the principal solid substances composing the outer crust 

 is as two and a half times the weight of water ; and this, 

 we know, if the globe were solid and cold, should 

 increase vastly towards the centre, water acquiring the 

 density of quicksilver at 362 miles below the surface, 

 and other things in proportion, and these densities 

 becoming much greater at greater depths ; so that the 

 entire mass of a cool globe should be of a gravity 

 infinitely exceeding four and a half times the weight of 

 water. The only alternative supposition is, that the 

 central materials are greatly expanded or diffused by 

 some means ; and by what means could they be so 

 expanded but by heat? Indeed, the existence of this 

 central heat, a residuum of that which kept all matter in 

 a vaporiform chaos at first, is amongst the most solid 

 discoveries of modern science,*' and the support which it 

 gives to ' Herschel's explanation of the formation of 

 worlds is highly important. AVe shall hereafter see 

 what appear to be traces of an operation of this heat 



- The researches on this subject were conducted chiefly by the late 

 Laron Fourier, perpetual secretary to the Academy of Sciences of 

 I';u'i.«. .Sec his TliCorlc AnaJytlque de la ChaUur. 1822. 



