Scr. X. INTERNAL DENSITY OF THE EARTH. 73 



strated that the strata containing marine diluvia which 

 are in lofty situations, must have been formed at the 

 bottom of the ocean and afterward upheaved by the 

 action of subterraneous fires. Besides, it is clear from 

 the mensuration of the arcs of the meridian and the 

 length of the seconds' pendulum, as well as from the 

 lunar theory, that the internal strata and also the exter- 

 nal outline of the globe are elliptical, their centers being 

 coincident and their axes identical with that of the sur- 

 face a state of things which, according to the distin- 

 guished author lately quoted, is incompatible with a 

 subsequent accommodation of the surface to a new and 

 different state of rotation from that which determined 

 the original distribution of the component matter. Thus 

 amid the mighty revolutions which have swept innumer- 

 able races of organized beings from the earth, which 

 have elevated plains and buried mountains in the ocean, 

 the rotation of the earth and the position of the axis on 

 its surface have undergone but slight variations. 



The strata of the terrestrial spheroid are not only 

 concentric and elliptical, but the lunar inequalities show 

 that they increase in density from the surface of the 

 earth to its center. This would certainly have happened 

 if the earth had originally been fluid, for the denser parts 

 must have subsided toward the center as it approached 

 a state of equilibrium. But the enormous pressure of 

 the superincumbent mass is a sufficient cause for the 

 phenomenon. Professor Leslie observes that air com- 

 pressed into the fiftieth part of its volume has its elas- 

 ticity fifty times augmented. If it continues to contract 

 at that rate, it would, from its own incumbent weight, 

 acquire the density of water at the depth of thirty-four 

 miles. But water itself would have its density doubled 

 at the depth of ninety-three miles, and would even at- 

 tain the density of quicksilver at a depth of 362 miles. 

 Descending therefore toward the center through nearly 

 4000 miles, the condensation of ordinary substances 

 would surpass the utmost powers of conception. Dr. 

 Young says that steel would be compressed into one- 

 fourth and stone into one-eighth of its bjilk at the earth's 

 center. However, we are yet ignorant of the laws of 

 compression of solid bodies beyond a Certain limit ; from 

 G 



