of a homogeneous fluid mass that revolves upon an axis. 115 
fluid below it in one body are in the same proportion to one 
another, as the pressures of the stratum upon the fluid below 
it in the other body. But in the body in equilibrio, the pres- 
sures at all points are equal ; wherefore, in the other body, a 
stratum likewise presses equably upon the fluid below it. 
And what is true of each individual stratum, must be true 
of the accumulated pressure of any number of superincum- 
bent strata. 
Thus, in the two bodies, every thing is similar. The forces 
which urge the particles of one, are, in the case of the other, 
all increased, or all diminished, in the same proportion, while 
they act in like directions. If, in the one, the gravity be 
every where perpendicular to the level surfaces ; the like 
force is perpendicular to the surfaces similarly traced in the 
other : and if, in the first, all the level strata press equably 
upon the fluid below them ; the same thing is true of the 
strata into which the second is divided. Wherefore, the 
equilibrium of one body is a necessary consequence of the 
equilibrium of the other, 
Proposition II. 
If a homogeneous fluid mass revolve about an axis, and be 
in equilibrio by the attraction of its particles in the inverse 
proportion of the square of the distance ; all the level surfaces 
will be similar to the outer one : and any stratum of the fluid 
contained between two level surfaces will attract particles in 
the inside with equal force in opposite directions. 
Suppose that the homogeneous fluid body R S T, revolving 
about the axis A B, is in equilibrio by the centrifugal force, 
and the attraction of its particles in the inverse proportion of 
