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Ch. XXXII,] SUPPOSED CENTEAL FLUIDITY OF THE EAPTH. 199 



from volcanic vents liave been observed to bave tbeir tem- 

 perature suddenly raised or lowered^ and tlie volume of tbeir 

 water increased or lessened, by subterranean movements. 



All these appearances are evidently more or less connected 

 with the passage of beat from the interior of the earth to 

 the surface; and where there are active volcanos, there 

 must exists at some unknown depth below, enormous masses 

 of matter intensely heated, and, in many instances, in a 

 constant state of fusion. We have first, then, to enquire, 

 whence is this heat derived ? 



It 



has long been 



Supposed central fluidity of the earth.— 

 a favourite conjecture, that the whole of our planet was 

 originally in a state of igneous fusion, and that the central 



parts still retain a great portion of their primitive heat. 



Some have imagined, with the late Sir W. Herschel, that the 

 elementary matter of the earth may have been first in a 

 gaseous fetate, resembling those nebulae which we behold in 

 the heavens, and which are of dimensions so vast, that some 

 of them w^ould fill the orbits of the remotest planets of our 

 system. The increased power of the telescope has of late 

 years resolved the greater number of these nebulous ap- 

 pearances into clusters of stars ; but so long as they were 

 confidently supposed to consist of aeriform matter, it was a 

 favourite conjecture that they might, if concentrated^ form 

 solid spheres ; and it was also imagined that the evolution 

 of heat, attendant on condensation, might retain the ma- 

 terials of the new globes in a state of igneous fusion. 



Without dwelling on such speculations, which can only 

 have a distant bearing on geology, we may consider how far 

 the spheroidal form of the earth affords sufiicient ground 

 for presuming that its primitive condition was one of universal 

 fluidity. The discussion of this question would be superfluous, 

 were the doctrine of original fluidity less popular; for it 

 may well be asked, why the globe should be supposed to 

 have had a pristine shape difl^erent from the present one ? 

 why the terrestrial materials, when first called into existence, 

 or assembled together in one place, should not have been 

 subject to rotation, so as to assume at once that form 



