546 
MR. HENNESSY’S RESEARCHES IN TERRESTRIAL PHYSICS. 
The value of the earth’s moment of inertia used in these calculations, was deduced 
by using- the value of p found in Section IX., and that of X found from the lunar 
inequalities. If the value of the latter quantity, found in the section referred to, 
were used, the resulting values of E would all be a little smaller ; it may therefore be 
concluded, that the earth's primitive ellipticity was less than its present ellipticity, 
although the difference between them may he neglected. 
(4.) The Direction of great Lines of Elevation on the Surface of the Earth. 
26. If a zone of least disturbance existed near the parallel of mean pressure, the 
directions of great lines of elevation should be nearly parallel or perpendicular 
to the equator. Its non-existence there, which observation seems to show, proves at 
least that the variable pressure did not predominate over the constant pressure. 
As yet, observation seems to prove that such a zone does not exist on the earth’s 
surface ; and hence from Section VIII. we must provisionally conclude that the con- 
stant pressure greatly predominated over the variable pressure, and consequently 
that the directions of lines of elevation must be comparatively arbitrary. Geological 
and geographical observations present results which are generally in accordance with 
these views. 
(5.) The Existence of great Friction and Pressure at the Surface of Contact of the 
Nucleus and Shell. 
27 . The conclusions arrived at in Section IV., combined with the important result 
obtained by Mr. Hopkins in his second memoir on Physical Geology*, show that 
great friction and pressure must exist between the shell and fluid nucleus. The 
result alluded to, as quoted in Mr. Hopkins’s third memoir, is 
where P denotes the precession of a solid homogeneous spheroid of which the ellipti- 
city=Si, that of the earth’s exterior surface, and P' the precession of the earth, sup- 
posed to consist of a heterogeneous fluid nucleus contained in a heterogeneous sphe- 
roidal shell, of which the interior and exterior ellipticities are respectively s and Si, the 
transition being immediate from the entire solidity of the shell to the perfect fluidity 
of the mass.” This result was found on the hypothesis of the non-existence of friction 
and pressure from molecular causes at the surface of contact of the shell and nucleus ; 
if this hypothesis were true, we should have in general, from articles 12 and 13, 
V’ Z Pj, or at least, we could not have P '7 Pj. This result is so different from that 
obtained by this observation, that we are entitled to assume that the motion of rota- 
tion of both shell and nucleus takes place nearly as if the mass were entirely solid. 
It must evidently result, that at the surface of contact of the solid and fluid, a con- 
* Philosophical Transactions, 1840, p. 207. 
