( 99 ) 
and that the mean Force of Gravity on the Surface 
will be to the Excefs of the Gravity at the Pole 
above that at F, as the mean Diameter multiplied 
into the Square of the Radius is to one fifth of the 
Difference of the longeft and fhorteft Diameters 
multiplied into the Square of the Co-fine of Lati- 
tude at F. 
2. The Decrement of Gravity from the Pole to 
the Equator is proportional to the Square of the 
Co-fine of Latitude; or, which comes to the fame, 
the Increment of Gravity from the Equator to the 
Pole is proportional to the Sine of Latitude. Hither- 
to I have confider’d the Variation of Gravity which 
arifes from the fpheroidical Figure, while it does not 
turn round its Axis ; but if it doth, the Direction 
of Gravity will be in the Line F G, perpendicular 
to the Surface ; and its Variation now arifing from 
both the Figure and centrifugal Force, will be five 
times greater than what arifes from the Figure alone ; 
as will appear from the Proportion of the Lines F H 
and F G, the former being to the latter, as the whole 
Force of Gravity at F, while the Speroid is at reft, 
to the Force with which a Body defcends at F, while 
it turns round its Axis. 
3. From this laft Article it appears, that one fifth 
of the Variation of Gravity is occafion’d by the 
Figure of the Spheroid, and the remaining four 
fifths by the centrifugal Force. And whereas the 
Earth could not be of an oblate fpheroidical Figure, 
unlefs it turned round its Axis ; nor could it turn 
round its Axis, without putting on that Figure : I 
fay, that the Diminution of Gravity towards the 
Equator, known by the Experiments with Pendu- 
1 Ium $ 5 
