34 



On the Density and 



a column of about ten million feet in height ; nor has any solid 

 been observed, except ice, in which it stands so low as five 

 million. But ten million feet is nearly half the length of the 

 earth's axis ; so that one millionth of the axis would be two 

 millionths of this modulus ; and the pressure of such a column 

 would consequently produce a variation of two millionths in the 

 density of a solid, or at most of 3 or 4 in the most compressible, 

 and In none so much as 5 or 5|. It must therefore be allowed, 

 that this part of the hypothesis is inconsistent with direct 

 observation. 



There is the less occasion for encountering any of these diffi- 

 culties, as we shall find that the theory of compressibility, in its 

 original form, is abundantly capable of representing the most 

 probable results of all the observations, which it is intended to 

 connect. The truth of this assertion will appear from the in- 

 spection of a table, which shows the compressibility and ellip- 

 ticity corresponding to different suppositions respecting the spe- 

 cific gravity of the earth's surface, taking 5.4, as sufficiently 

 demonstrated, for the mean density. 



From this table we may easily deduce the intermediate re- 

 sults by interpolation : thus, if the ellipticity were found exactly 

 3-ig^, we should have for the superficial density 2.73, or 2', and 

 for the height of the modulus 9 650 000 feet. 



In these calculations, it has not been necessary to have re- 



