PRESSURE AND VOLUME. 365 



gravity than any with which we are acquainted. Indeed, the interior 

 pressures increase so rapidly with depth that rearrangement might occur 

 again and again. Therefore, even if the average chemical composition be 

 the same deep within the earth as at the surface, in the centrosphere, in 

 consequence of high pressure, there may be a set of silicate minerals which 

 have as high a specific gravity as the average density of the earth, viz, 

 5.67. If the accepted theory as to the distance between molecules be cor- 

 rect, viz, that molecules of ordinary liquids at the surface of the earth do not 

 occupy more than one-third of the total volume,™ there is ample room 

 between them for the condensed rearrangement suggested. From the fore- 

 going it appears that we do not necessarily appeal to a great preponderance 

 of heavy metals deep within the earth to explain its average high specific 

 gravity. It may be very largely explained by the condensation of the 

 material due to pressure. If, as suggested by Chamberlin, the average 

 specific gravity of the material of the earth be that of meteoric falls, the 

 average change in specific gravity would be from 3.69 to 5.67 as a result of 

 pressure. The great increase in the average specific gravity of minerals 

 with increase of pressure in the crust of the earth would seem to make the 

 estimate of the change in average specific gravity of the minerals from 3.69 

 to 5.67, as a result of the very great pressures deep within the earth, a very 

 modest one. 



While I have no doubt that the condensation of the earth material into 

 heavier compounds as a result of pressure is a partial explanation of the 

 high specific gravity of the earth, I by no means urge this as the sole cause. 

 Indeed, it is probable that the segregation of heavy material toward the 

 center and lighter material toward the surface has steadily continued 

 throughout geological time, and therefore the difference in composition is a 

 very important factor in the difference in density at the surface and the 

 center. But I do not venture even a guess as to the relative importance of 

 the two factors of condensed compounds and segregation of material in 

 explaining the increase in density of the material of the earth with increase 

 of depth. 



«Nernst, W., Theoretical chemistry, trans, by 0. S. Palmer, Macmillan & Co., London, 1895, 

 p. 196. 



