( i8 6 ) 
I do not doubt but Monf. Mairan will be of this 
Opinion, when he has carefully and impartially examin’d 
the ixth and 13th Sections of the Firft Book of Sir /- 
faac Newton'* Trincipia,\n& the 1 8 th, 19 th, and 20th 
Trof. of the Third Book. And if he will be at the 
Pains to compare the 38th and 39th Tropoftion of the 
Third Book with the 66th of the Firft, he will hnd 
that the Preceflion of the ./Equinoxes is owing to the 
broad fpheroidical Figure of the Earth ; and that if it 
had Monf. Caffini's Figure, the .Equinodial Points wou’d 
move in Confequentia fafter than they do now in An- 
tecedents. 
Further, Monf. Mairan demonftrates, that in an ob- 
long Spheroid, the Diminution of Gravity, by the Cen- 
trifugal Force, encreafes fafter in going from the Poles 
to the ./Equator, than it wou’d do in a Sphere, and fafter 
in a Sphere than it wou’d do in a broad Spheroid ; and 
therefore wou’d fhew, w That notwithftanding the Sur- 
“ face of the Earth is nearer to the Center in Mov\[.Caf 
“ Jini's Figure than in Sir I faac Newton' s, yet the 
“ Centrifugal Force will dimimfh the Gravity fo faftin 
u going from Tar is to the ./Equator, that the fhortening 
“ of Pendulums, to make them fwing Seconds at the 
<• ./Equator, may very well be accounted for that Way.” 
Now let us examine into this Matter, to fee whether 
the Caufe is adequate to the Effe<ft. 
If the Diftance from the Surface of the Earth at the 
Pole to the Center be 96, and the Diftance of the Sur- 
face at the .Equator be 95*, the Diftance of the Surface 
at Taris , in the Latitude of 48° 5c/, will be 95-, 562, &c. 
by the Property of the. EllipFe. Now lince the Force 
of Gravity, in different Places on the Earth’s Surface, is 
reciprocally as the Diftance from the Center, and the 
Lengths of Pendulums, that perform their Vibrations in 
the fame Time, are diredly as the Force of Gravity ; 
therefore 
