would bethe confequenc6 ofarefiftence from ^Medium, 
either in the fimple or duplicate of the Velocity, or 
^Ife between both; and tocompleat this Argument is laid 
down a general Method of determining the denfity of tiie 
Medmm in all places,, which, with a uniform Gravity ten- 
ding perpendieukrly to the plain of die Hor^zo^, fliall 
make a Project move in any curve Line affigned ; which 
is thQ loth. Prop. Lib. II. Then the circular Motion of 
Bodies in refiftmg Media is deternimed, and 'tis fliown 
under what Laws of decreafe of Denfity, the Circle will 
become a proportional Spiral. Next the denfity and com- 
preflion of Fluids is confidered, and the DoStrine of H}* 
drofiatkks demonftrated ; and here 'tis propofed to the 
Contemplation of Natural Pliilofbphers, whether the fur- 
prizing Phenomena of the Elafticity of the Air and fomeo- 
ther Fluids may not arife from thek being compofed of 
Particles which flie each other ; which being rather a 
Ehyfieal thaa Mathematical Inquiry, our Author forbears 
to Difcufs. 
Next the Oppofition of the Medium and its EflPecls on 
the Vibrations of the Pendulum is confidered, which is 
followed by an Inquiry into the Rules of the Oppofition 
to Bodies, as their Bulk, Shape, or Denfity may be vary- 
ed : Here with great exa£tnefs is an Account given of fe- 
veral Experiments tried with PenduU^moK^tx to verify the 
aforegoing Speculation, and to determine the quantity 
of the Airs Oppofition to Bodies moving in it. 
From hence is proceeded to the undulation of Fluids, 
the Laws whereof are here laid down, and by them the 
Motion and Propagation of Light and Sound are explai- 
ned. The lart Section of this Book is concerning the Cir- 
cular Motion of Fluids, wherein the Nature of their F^^r- 
jT/W Motions is confidered, and from thence the Cartejian 
Doftrine of tliQ Fortices of the Celefl:ial Matter carrying 
with them the Planets about the Sm^ is proved to be 
alltogether impoflible. 
