Over the ellipsoid, p denoting the length of the perpendicular from the centre on a tangent plane, px _ **pv** _ _ pz 1= a2+X' b +A' n c2+A p2x2 + p2y2 p2z2 I (a2 - + X)2 (b 2 +x)2 + (0+X)2, p 2 = (a2+A)12+(b2+X)m2+(c2+X)n2, = a 2 1 2 +b 2 m 2 +c 2 n 2 +X, 2p d = ds; (8) Thence d?

Ramsay and Shields suggested that there exists an equation for the surface energy of liquids, analogous to the volume-energy equation of gases, **PV** = RT.

Since dE=dH - pdv, we have evidently for the variation of the total heat from the second expression (8), dF=d(E + **pv**) =dH+vdp=Sde - (Odv/de - v)dp .

In thiscase the ratio of the specific heats is constant as well as the difference, and the adiabatic equation takes the simple form, **pv** v = constant, which is at once obtained by integrating the equation for the adiabatic elasticity, - v(dp/dv) =yp.

The most natural method of procedure is to observe the deviations from Boyle's law by measuring the changes of **pv** at various constant temperatures.