[ 549 3 
cOnd Fluxion of the Diftance of the Moon from that 
Plane, the Second and Third meafure the Second 
Fluxions of her Diftances from the Line of the Qua- 
dratures, and from the Line of the Syzigies , refpec- 
tively. Hence a Conftruttion is derived of the Tra- 
jedfory which would be deferibed by the Moon about 
the Earth, in confequence of their unequal Gravita- 
tion towards the Sun, if the Gravity of the Moon 
towards the Earth was as her Diftance from it. From 
this a Computation is deduced of the Motion of the 
Nodes of the Moon, and of the Variation of the in- 
clination of the Plane of her Orbit, which we cannot 
deferibe here. It is fufficient to obferve, that thefe 
Motions are found to agree nearly with thofe which 
have been deduced from other Theories, and from 
Agronomical Obfervations. 
A Fluid being fuppofed to gravitate towards two 
given Centres with equal and invariable Forces, it is 
fhewn, that the Figure of the Fluid mud be that of an 
oblong Spheroid, and that thofe two Centres muft 
be the Foci of the generating Ellipfe. The Nature 
of the Figure is alfo fhewn, when the Fluid gravitates 
towards feveral Centres, or when it revolves on its 
Axis; but thefe are mentioned briefly, becaufe fucii 
Theories are of little or no U.fe for difeovering the 
Figures of the Planets. 
In the 1 2th Chapter, the Author proceeds to con- 
fider the more concife Methods, by which the Fluxions 
of Quantities are ufually determined, and to deduce 
general Theorems more immediately applicable to 
the Refolution of Geometrical and Philofophicai 
Problems. In the Method of Inhnitefimals, the Ele- 
ment, by which any Quantity increafcs or decreafes, 
Y y 2 is 
