PreceJJion of the Equinoxes. 507 
communicate a motion to its parts. Suppofe we knew 
the precife difturbing force of the Sun upon any one 
particle of this ring according to its fituation ; in that cafe 
we could eatily find the velocity which would be com- 
municated to fuch a particle in any given time ; but the 
mutual actions of the fluid particles upon each other 
could never be exactly eftimated, much lefs their efiedts 
in endeavouring to turn the whole earth round its cen- 
ter. However, it is eafy to fee, that in the cafe of a hard 
ring of matter cohering clofe with the furface of the 
earth at the equator,, both the law by which the particles 
adt on each other, and on the whole mafs of the earth,, 
will be widely different from the cafe of fluidity, and the 
effedts much greater in altering the pofition of the axis 
of rotation. 
To explain this by an eafy example (fig- 1,) let a, r, 
and c, reprefent three fmall bodies in the fame horizon- 
tal line ae. Suppofe a to defcend by any accelerating 
force as gravity ; b to defcend by the fame force, a lefs or a 
greater; and c not to be adted upon at all: in every one 
of thefe cafes the bodies a and b will defcend with their 
refpedtive velocities, and the body c will preferve its 
fituation. If a and b are fmall particles of fluid of any 
form* and c a hard one, and if the particle a be placed 
3. in, 
