[ W 1 
Motion continually incrcafes, but by a Mean between 
thefe Spaces. 
When the Sides of a Redangle increafe or decreafe 
with uniform Motions, it may be always confldered 
as the Sum or Difference of a Triangle and Trape- 
zium \ and its Fluxion is derived from the laft Pro- 
portion. If the Sides increafe with uniform Mo- 
tions, the Redangle increafes with an accelerated 
Motion ; and in meafuring this Motion at any Term 
of the Time, a Part of the Increment of the Rectangle, 
that is here determined, is reje&ed, as generated in 
confequence of the Acceleration of that Motion. 
The Fluxions of a curvilineal Area (whether it be 
generated by an Ordinate moving parallel to itfelf, 
or by a Ray revolving about a given Centre) and of 
the Solid, generated by the Area revolving about the 
Bale, are determined by Demonftrations of the fame 
kind and when the Ordinates of the Figure increafe, 
the Increment of the Area is refolved in like man- 
ner into Two Parts, one of which is only to be re- 
tained in meafuring the Fluxion of the Area, the 
other being rejected as generated in confequence of 
the Acceleration of the Motion with which the 
Figure flows. An Uluflration of Second and Third 
Fluxions is given by refolving the Increment of a 
Pyramid or Cone into the feveral refpeddve Parts 
that are conceived to be generated in confequence of 
the Fii TF, Second, and Third Fluxions of the Solid, 
when the Axis is fuppofed to flow uniformly. 
In Chap. V. a Series of Lines in Geometrical Pro- 
greflion are reprefented by an cafy Conftru&ion. 
The Firft Term being fuppofed invariable, and the 
Second to increafe uniformly, all the fubfequent 
Terms 
