[ *9* 3 
XIX. Let us now fuppofe, that 
jfafiv Vh a e n Axes°!f the centrifugal Force at the Equa- 
te spheroid, the tor is known by Obfervation, as 
Variation of the a [f Q within the Earth, &c. and that 
Densities of the 
Strata being taken 
at pleafure. 
it is a certain Part - of the Gravity ; 
by Articles XIV. and XVI. we fhall 
have this Equation : 
r I 4-p ~ 
2 C fe ' • 
2 D' 
3 + P 
“ r I+P I+q 
2Cfe ' r et | 2 C g C 1 n 
2_q 
2 c 2 e 
t + q, 
3 + P*5 + P 
_ 8cf m e 
3 + q 
8c mge 
o .. 
! + q. 
+ q x 5+q 3 + pxj+p 3 + qM+q 
From hence it will be eafy to derive the Value of x, 
becaufe f,g,p,q, will be given, from the Hypothefis 
that will be chofen, for the Variation of the Denfity 
in the internal Parts of the Spheroid. 
XX. And if on the contrary a. be given, that is, if 
we know by Obfervation the Ratio of the Axes of 
the Planet concern’d; then by the foregoing Equation 
we may perceive, whether we have afl'umcd an agree- 
able Hypothefis For the Variation of the Denfities : 
But we cannot precifely determine what this Hypo- 
thefis muft be, becaufe there is but one Equation, in 
which four indeterminate Quantities f, g, p, q, are in- 
volved* And indeed there might be many more than 
four indeterminate Quantities, if we Ihould aflume 
more than two Terms in the general Equation of the 
Denfities D=fr p -Jrgr <1 -j-hr s , &c. 
XXI. In order to apply the foregoing Theory to the 
Earth, it might feem at firft Sight, that by the Afllft- 
ance of Obfervations made for meafuring the Length 
of 
