88 Prof. Leslie on tlie Theory of Compression applied fo 



expressed by 764 with 1 6G cyphers annexed, while Water would 

 be condensed 3009000 times, and Marble acquire the density of 

 119. 



Such are the prodigious results deduced from the law of gra- 

 vitation, even supposing the structure of the globe were uni- 

 form. But if we take into the estimate the augmented power 

 from condensation, the numbers would become still more stu- 

 pendous. It follows, therefore, that if the great body of our 

 earth consisted of any such materials as we are acquainted with, 

 its mean density would very far surpass the limits assigned by 

 the most accurate investigations. The astronomical observa- 

 tion by Dr Maskelyne on the deflection of a pendulum, caused 

 by the attraction of the sides of Mount Schehallien, and the nice 

 experiments made with the Balance of Torsion by Mr Caven- 

 dish, on the mutual action of ponderous balls of lead, — nearly 

 concur in representing the mean density of the globe as only about 

 Jive times greater than that of water. It seems, therefore, to 

 follow conclusively, that our planet must have a very widely 

 cavernous structure, and that we tread on a crust or shell whose 

 thickness bears but a very small proportion to the diameter of 

 its sphere. Physical science can extend her prospects to the 

 farthest verge of possibilities ; but Chemistry, even in its pre- 

 sent advanced stage, fails altogether in aiding inquiry ; and the 

 various hypotheses framed by geologists are built with such 

 scanty and slender materials, as to furnish no safe guidance 

 through those boundless speculations. 



It is evident, that immense compression would totally derange 

 the powers of elective attraction, and change the whole form 

 ^nd constitution of bodies. When air becomes denser than gold, 

 it is hard to conjecture what transmutations this plastic fluid 

 must undergo, The bowels of the earth may contain substances 

 thus transformed, bearing no longer any resemblance to their 

 aspect on its surface. 



But since an absolute void is inadmissible, the vast subter- 

 ranean cavity must be filled with some very diff*usive medium, 

 of astonishing elasticity, or internal repulsion among its mole- 

 cules. The only fluid we know possessing that character is 

 Light itself, which, when embodied, constitutes Elemental Heat 

 ' or Fire. It is elicited from every substance by percussion or 



