VOL. XXXIII.] I'HILOSOPHICAL TRANSACTIONS. 67 



going from the poles to the equator, in such a figure of the earth, with the 

 lengths that pendulums must have to swing seconds in several latitudes; from 

 a comparison of the lengths of pendulums, observed by different persons to be 

 shorter towards the equator than in greater latitudes, when they swing seconds, 

 he shows that the earth must be 31-iV miles higher at the equator than at the 

 poles; and therefore that it must be denser towards the central than the superficial 

 parts, to produce a flatted spheroid, where the equatorial diameter must exceed 

 the axis so much more; that is, be longer something more than —^^ part. 



Lastly, let us suppose the earth, at its first creation, to have been made of 

 land and water, the first as solid, and the last as fluid as it is now, but of M. 

 Cassini's figure, and examine the consequence. Since in that figure the axis is 

 -jij- part longer than the equatorial diameter; the gravity will be so much greater 

 at the equator than at the poles, that the waters will all flow to the equatorial, 

 and leave the polar regions; which will happen still more by the centrifugal 

 force, which the earth in its diurnal motion will give to the fluid; and therefore 

 the sea would be 43-fi-f^ miles higher at the equator than at the poles, which 

 must overflow all the torrid zone, and leave the polar regions dry. 



Now if we suppose the same figure of the earth, but the land, at its first 

 creation, as firm as it is now, it will in that case follow from M. Mairan's prin- 

 ciples, that the sea must rise and overflow all the equatorial regions, though 

 the earth had no diurnal revolution; and much more so, when the centrifugal 

 force, arising from the diurnal motion, helps to carry the water the same way. 



Having shown that M. Mairan's account of the action of gravity, on several 

 places upon the earth's surface, can be of no service for reconciling the experi- 

 ments made on pendulums, with the figure of the earth deduced from M. Cas- 

 sini's measures; Dr. D. proceeds to show that his demonstrations are founded 

 on wrong principles. And flrst, in regard to gravity. 



This gentleman has followed Sir Isaac Newton, in saying, that gravity in- 

 creases in a duplicate reciprocal proportion of the diminished distance from the 

 centre of the force, and so vice versa ; but he has followed Sir Isaac Newton no 

 farther than served his present purpose; otherwise he would have known, that 

 in respect to a central body, as a planet, towards which otlrers are urged by 

 gravity, this law obtains only, as bodies attracted are removed from the surface 

 of the planet to greater distances from the centre compared with that distance, 

 or as from greater distances they approach nearer to the planet; that the greatest 

 action of gravity is at the surface of the planet ; that afterwards in advancing 

 towards the centre, the force of gravity on the body attracted continually grows 

 less, decreasing directly as the distance; and that this holds true in a spheroid 

 as welt as a sphere; that on different parts of the surface of the earth, the 



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