C 35 8 ] 
fame manner. The Nature of the Line that among 
nil thofc of the fame Perimeter is deferibed in the 
lead Time, is difeovered with great Facility, by de- 
termining from the former Cafe the Property of the 
Figure when the Sum or Difference of the Time in 
which it is deferibed by the defeending Body, and of 
the Time in which it would be deferibed by any 
given uniform Motion, is a Minimum ; for the latter 
Time being the fame in all Curves of the fame 
Length, it follows that the Figure, which has this Pro- 
perty, muft be deferibed in lefs Time than any other 
of an equal Perimeter. The general Ifoperime- 
trical Problems are refolved, and the Solutions are 
rendered more general, with like Facility by the 
lame Method j which is alfo applied for determining 
the Property of the Solid of leaft Refiftance, and 
ferves for refolving the Problem, when Limitations 
are added concerning the Capacity of the Solid, or 
the Surface that bounds it. 
The laft Chapter of the Firft Book treats chiefly of 
Gravitation towards Spheroids, of the Figure of the 
Planets, and of the Tides. The Author, having Oc- 
cafion in thofe Inquiries for feveral new Properties 
of the Ellipfe, begins this Chapter by deriving its 
Properties from thofe of the Circle, by confidering it 
as the oblique Section of a Cylinder, or as the Pro- 
jection of the Circle by parallel Rays upon a Plane 
oblique to the Circle. In this manner the Properties 
are briefly transferred from the one to the other, be- 
caufe by this Projection the Centre of the Circle gives 
the Centre of the Ellipfe 5 Diameters perpendicular to 
each other in the Circle with their Ordinates, and the 
circumfcribedcSquare, give conjugate Diameters of 
