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MR. HENNESSY’S RESEARCHES IN TERRESTRIAL PHYSICS. 
different at first, it seems probable that the influence of frietion, and of the cohesion 
of their surfaces of contact, would at length establish an uniform motion for the whole 
mass. The direct influence which the rotatory motion of the shell and nucleus may 
exercise upon geological phenomena, will not require therefore the motions of both 
to be separately considered. 
The examination of the motions of the shell and nucleus, and of their mutual 
actions, whether directly, or from the influence of exterior disturbing causes, may 
therefore be comprehended under the following divisions : — 
1. The phenomena attending the rotation of the entire mass during the gradual 
solidification of the shell. 
2. The pressures exerted by the fluid upon the interior surface of the shell, whether 
from molecular action, the agency of the heavenly bodies, or from centrifugal force. 
3. The influence of the changes of temperature which may occur during the soli- 
dification of the shell in contracting or expanding its parts, and in producing physical 
changes in its interior structure. 
From the intimate connexion between the first and second of the above divisions, 
it would be impossible to examine one of them in a perfectly general manner without 
introducing the consideration of the other. The complete consideration of both could 
with great advantage be treated in another memoir than in the present, and 1 hope 
soon to have it in my power to complete all the necessary investigations. It will be 
enough for the present to indicate the importance of the first division in a geological 
point of view, by referring to one of the phenomena comprehended under it. If from 
the formation of the solid shell, and from the gradual diminution in the mass of 
the fluid nucleus, any change should be produced in the moment of inertia of the 
whole mass with respect to its axis of rotation, the angular velocity of the globe 
about its axis would be changed. The manner in whieh the solidification of the 
mass may take place, and the probable constitution of the fluid, will determine how 
far such a change may extend. If such a change should be great, it would exert an 
important influence upon the motions of the liquids or gases surrounding the earth, 
and upon a multitude of organic phenomena which its surface may have presented 
at different times. 
