MR. HENNESSY’S RESEARCHES IN TERRESTRIAL PHYSICS. 
507 
fectly cooled solidified matter there, as the matter formerly ejected did when the 
solid surface was itself at a very high temperature. From the foregoing considera- 
tions, it appears that a value of less than the present semipolar axis of the earth 
would be at least as much in accordance with observed geological phenomena as a 
value greater than that semiaxis. The protrusion of the primary and igneous rocks 
through the strata composing the external crust of the earth, would be in some 
measure a necessary consequence of the smaller value of a, ; and it would not follow 
that the surface of the earth should necessarily undergo any great contortions. 
In either of the cases which have been just examined, the arrangement of the 
molecules constituting the fluid globe should be different from their present arrange- 
ment. Their arrangement may or may not be different, if the value of coincided 
with the present semipolar axis of the earth, in so far as the value of a, would have 
any influence upon that arrangement. 
If the dimensions of the globe had been increasing in the manner which should 
happen if had at first a small value, the rate of that increase could be determined 
by finding the areas of the fissures through which the fused matter may have been 
ejected during the progress of the different geological formations. The geometrical 
relations between the surface of the spheroid and its axes would evidently be of some 
assistance in the course of such an investigation. If the sum of the areas of these 
fissures was small, compared with that of the surface of the earth, then it may be 
generally concluded that could not be much less than the present semipolar axis of 
the terrestrial spheroid. 
The three following general conclusions may be now stated as deductions from the 
foregoing remarks : — 
1. If «i were greater than the present semipolar axis of the earth, the difference 
should be small. 
2. If a, were less than that semiaxis, it becomes more difficult to assign a limit to 
their difference, but it appears probable that this difference would be greater than 
what it would be in the foregoing case. 
3. The value of a, may be identical with that of the present semipolar axis without 
contradicting any properties of the primitive fluid mass of which we may be aware, 
or without discordance with geological phenomena. 
In order that the value of Ui should be greater than the present semipolar axis, it is 
evident that the fluid should have either a low density or a small compressibility. If 
«! were, on the contrary, much less than that semiaxis, the specific gravity of the fluid 
should be high or its compressibility should be great. If were equal to the semi- 
polar axis, the fluid’s compressibility should still be small compared with those of all 
the fluids, except mercury, upon which experiments have been made, unless its density 
were much less than the mean density of the present external crust of the earth. 
The above considerations, in addition to what have been previously presented, appear 
to prove that a, could not much exceed the present semipolar axis of the earth, and 
