SEQUEL TO THE EPOCH OF NEWTON. 251 



Ellipticity, by which the effect is produced. But it 

 is found, upon calculation, that we cannot obtain 

 this determination without assuming some law of 

 density in the homogeneous strata of which we 

 suppose the earth to consist 39 . The density will 

 certainly increase in proceeding towards the center, 

 and there is a simple and probable law of this 

 increase, which will give 1 -300th for the Ellipticity, 

 from the amount of two lunar Inequalities, (one in 

 latitude and one in longitude,) which are produced 

 by the earth's oblateness. Nearly the same result 

 follows from the quantity of Nutation. Thus every- 

 things tends to convince us that the ellipticity can- 

 not deviate much from this fraction (Q). 



Sect. 7. Confirmation of the Newtonian Theory 

 by Experiments on Attraction. 



THE attraction of all the parts of the earth to one 

 another was thus proved by experiments, in which 

 the whole mass of the earth is concerned. But 

 attempts have also been made to measure the 

 attraction of smaller portions; as mountains, or 

 artificial masses. This is an experiment of great 

 difficulty; for the attraction of such masses must 

 be compared with that of the earth, of which it is a 

 scarcely-perceptible fraction ; and, moreover, in the 

 case of mountains, the effect of the mountain will 

 be modified or disguised by unknown or unappre- 



39 Airy. Fig. Earth, p. 235. 



