[435 3 
ceffive degrees, by which knowledge has been aug- 
mented to that pitch, in which we now behold it. 
The antients were well acquainted with the ro- 
tundity of the earth, and were fatisfied, that heavy 
bodies, in every place, had a tendency to its center : 
but they had never any fufpicion, that the force of 
their tendency to the center was greater in one 
country than another, or that, when dropped from 
any hight, they fell fafter in one latitude than another. 
The great Huygens, who fir ft fet the do&rine of 
centrifugal forces in a clearer light, law plainly, that 
the weight of bodies muft naturally be lefs at the 
equator, than at the poles ; their great velocity there 
round the earth’s axis taking off part of the weight, 
which they acquire by their gravitation towards the 
center of the earth. And, though he was not quite 
exadt in fettling the true proportion of the force of 
gravity in different latitudes; yet we owe this obli- 
gation to him, of having made the firft difcovery of 
a thing, which hath fince been the ground of fo 
many theories and experiments. 
Mr. Richer, when he went to the ifland of Cayenne, 
made the firft experimental proof of the decreafe of 
gravity, in approaching the equator, though he was 
not led thereto by Huygens’s theory, which was then 
but lately publilhed, and not fo generally known ; 
but, from finding his clock, which he had brought 
with him, go confiderably flower than it had gone 
in France. 
But Sir Ifaac Newton, firft of all, (hewed, how the 
variation of gravity in different latitudes depended not 
only upon the centrifugal force, but alfo upon the 
figure of the .earth, which he likewife determined, as 
well 
i 
