( 10O ) 
lams, prove both the Rotation and oblate fpheroi- 
dieal Figure of the Earth. 
4. The mean Force of Gravity on the Surface 
is to the centrifugal Force at any Point F, as a 
Rediangle under the Radius and mean Diameter to 
a Rediangle under the Co-fine of Latitude, and four 
fifths of the Difference of the longefi and ihorteft 
Diameters. And at the Equator, where the Co-fine 
of Latitude becomes equal to the Radius, the mean 
Force of Gravity is to the centrifugal Force, as the 
mean Diameter to four fifths of the longefi and 
Ihorteft Diameters. This Article is found from the 
Proportion cf the Lines F H and G H ; the former 
being to the latter as the Force of Gravity to the 
centrifugal Force. 
5*. The Proportion of the Diameters of the 
Earth will be found in the following manner : The 
Moon revolves about the Earth in 27 d , 7 h , 43', or 
in 39343 Minutes : And her mean Diftance is a- 
bout 5*9 \ Semidiameters of the Earth, according to 
La Hire's and Flamfl cad's Tables ; but near 60 i 
by Halley's Tables. I fliall therefore take 60 for 
the mean Diftance, till it be better known : Then 
according to the Nature of Gravity, as the Cube 
of the Moon’s Diftance to the Semidiameter of the 
Earth, or as 2x6000 to Unity, fo is 15*47870000 the 
Square of the periodick Time of the Moon to 7166, 
the Square of the Number of Minutes in which ano- 
ther Moon would revolve about the Earth at the 
Diftance of its Semidiameter. And as this laft 
Number to 2062096, the Square of 1436, the Num- 
ber of Minutes in a Sydereal Day, fo is Unity to 
x8 77 ; which would flievv the Proportion of the 
' centri- 
