( ) 
in Iflands, than they are found in fad. The Lon- 
don Pendulum ihould be longer when compared to 
the Tarts one, than it really is : The Jamaica 
Pendulum, when compared to the London one, 
which vibrates in a greater Ifland, Ihould be longer 
than is found by Experience \ and the Pendulum in 
Cayenne (a fmaller Ifland than Jamaica') ihould 
Hill be longer. This Defed of Gravity in Iflands 
is very probably occafioned by the Vicinity of 
a great Quantity of W ater, which being fpecifically 
lighter than Land, attrads lefs in Proportion to its 
Bulk. And I find by Computation, that the Odds 
in the Pendulums betwixt Theory and Pradice is 
not greater than what may be accounted for on that 
Suppofition. I lhall alio obferve, that although 
the Matter of the Earth were entirely uniform, yet 
the Hypothefis of its being a true Spheroid is not 
near enough the Truth to give the Number of Vi- 
brations which a Pendulum makes in twenty-four 
Hours. And fnppofe the true Figure were known, 
the Inequalities of Mountains and Vallies, Land 
and Water, Heat and Cold, would never allow 
Theory and Experiments to agree. But after the 
French Gentlemen who are now about meafuring 
a Degree, and making Experiments with Pendulums 
in the North and South, fliall have finiihed their 
Defign, we may exped new Light in this Matter. 
O 2 
III. Filer! 
