304 



NO SENSIBLE CONTRACTION OF GLOBE. 



[Ch. XIII. 



The gradual diminution of the supposed primitive heat of 



the 



principal cause of alterations of climate. 



globe has been resorted to by many 



matter 



planet is imagined, in accordance with the conjectures of 

 Leibnitz, to have been originally in an intensely heated state, 

 and to have been parting ever since with portions of its heat, 

 and at the same time contracting its dimensions. There are. 

 undoubtedly, good 



from 



tion and experiment, that the temperature of the earth 

 increases as we descend from the surface to that slight depth 



man 



of a secular decrease of internal heat accompanied by con- 

 traction. On the contrary, Laplace has shown, by reference 

 to astronomical observations made in the time of Hipparchus, 

 that in the last two thousand years at least there has been 

 no sensible contraction of the globe by cooling ; for had this 

 been the case, even to an extremely small amount, the day 

 would have been shortened, whereas its length has certainly 

 not diminished during that period by 



3 



th of a second. 



I shall allude in the 

 lich may be urged ags 



volume to many objections 



of the earth's central nucleus, and shall then enquire how far 



the 



mentation of temperatur 

 may be referable to oth 



causes uncon- 



nected with the supposed pristine fluidity of the entire globe. 



In the same 



shifting of the position of the earth's axis of rotation and 

 of its centre of gravity; also of the supposed sliding of a 

 rigid crust over an internal fluid nucleus, recently advanced 

 by Mr. Evans to explain the altered climates of the habitable 

 surface in certain latitudes. 



