253 
force which is a function of the distance; and in the case of 
erystalline structure, also of the direction of the line joining 
the molecules. 
The general equation of equilibrium of a system is, 
(SS(x0 + von + 202) dm = \dvdadydz. (1) 
Mr. Haughton shows from the definition of the medium, that 
vV=V+%), 
where vp is a homogeneous function of the first Marie of 
the six quantities, 
d—& dyn df dyn , dt df , de dé . dy 
ye te ay Ete’ at a 
and v, a homogeneous function of the second order of the same 
quantities. The function vy is zero in a solid body, and not in 
a fluid ; which is equivalent to saying that in a solid body the 
molecular forces equilibrate each other without the aid of ex- 
ternal forces, but that in fluids this is not the case, and that 
consequently a fluid left to itself would be dissipated by the 
action of its own molecular forces ; this Mr. Haughton con- 
ceives to be true of all fluids, whether gaseous or liquid. It 
should be understood that the mutual gravitations of the par- 
ticles are not included among the molecular forces, but among 
the external forces. 
The values of v, and v, are shewn to be finally 
w=e(Gt ets) 2) 
2y,;= (2) + “(ze =z) a (2) + Le? + Mv? + Nw? 
LL RR 
+2(1t. EM dada de dy 
a (aati A "@) +0o(at+B *dy tye) 
ae 
shag (at a4 pa rm vq) } 
a) + 2(ayvw + Bouw + y,uv) 
