TRANSACTIONS OF THE SECTIONS. 25 
covers three-fourths of the entire spheroid, gravity would be perpendicular to it at 
every point. If, however, the earth were stripped of all its seas and oceans, the 
surface would present considerable inequalities. From what is now known regard- 
ing the depth of the ocean, the continents would appear as plateaus elevated above 
the oceanic depressions to an amount which, although small compared to the earth’s 
radius, would be considerable when compared to its outswelling at the equator, 
and its flattening towards the poles. The surface thus presented would be the 
true surface of the earth, and would not be perpendicular to gravity. If a mean 
surface be conceived intersecting this, so as to leave equal volumes above of eleva- 
tions, and of depressions below it, it is not allowable to assume that such a surface 
is perpendicular to gravity. The mean surface of the solid crust of the earth would 
not be perpendicular to gravity, if, after the process of solidification had commenced, 
any extensive changes in the distribution of matter in the earth’s interior could take 
place. If the fluid matter in solidifying underwent no change of volume, the forms 
of the strata of equal density within the earth would be the same as those of the 
primitive fluid mass, and would continue to be the same at every stage of its solidi- 
fication. But if, as observation indicates, such fused matter, on passing to the solid 
crystalline state, should diminish in volume, the pressure on the remaining strata of 
the fluid would be relieved, and they would tend to assume a greater ellipticity than 
they had when existing under a greater pressure. The general result of this action 
would manifestly be to produce a change in the direction of the attractive forces at 
the outer surface of the solid crust. The direction of a plumb-line would be altered 
so as to slightly increase the apparent latitudes of places over a zone intermediate 
between the equator and poles. 
On the Solidification of Fluids by Pressure. 
By Professor Hrnnessy, MRA. 
The views put forward were deduced from some propositions in the dynamical 
theory of heat contained in the writings of Prof. W. Thomson and Prof. Clausius. 
The general result arrived at regarding the influence of pressure on a fluid so cir- 
cumstanced as to lose no part of the heat acquired by condensation, would be, that 
so long as the matter continued in a fluid condition, the resistance to compression 
from this cause would be very small. If, however, the fluid were on the point of 
changing its state to that of solidity, the effect of the latent heat of fusion, which by 
hypothesis could not be emitted, would interpose a resistance of great magnitude 
compared to that resulting from simple compression. The fused matter of which 
the interior of the earth most probably consists, would be under conditions similar 
to those mentioned, from the slow conducting power of the materials composing 
the earth, and from the pressure of all the outermost strata of equilibrium of the 
fluid upon those néar the centre; and thus the influence of pressure in promoting 
solidification would be less than at its surface. 
On the relative Accuracy of the different Methods of determining 
Geographical Longitude. By Professor Loomis. 
The author first gave a rapid sketch of the several methods of determining differ- 
ences of longitude adopted by astronomers and geographers, and pointed out the 
degree of accuracy that might be expected from each; and drew, as the conclusion of 
this branch of his subject, the importance of obtaining a method far more accurate 
than any of the preceding, and in which the personal equations of the observers 
would either be eliminated or greatly reduced; and such a desideratum he considered 
was afforded by the electric telegraph. He then explained at length the various 
methods resorted to by Dr. Bache, Prof. Morse, himself, and other American philo- 
sophers, the chief peculiarity of which was using either a sidereal and mean-time 
clock at the recording-station ; the beats of these, coinciding every six minutes, gave 
well-marked equidistant points of time to which to refer the signals received every 
second from the observing end or station; or by using a sidereal clock and chrono= 
meter, beating twice each second, intervals of three minutes became similarly marked 
out. Then, by alternating the stations at which the observations were made and 
