MR. HENNESSY’S RESEARCHES IN TERRESTRIAL PHYSICS. 547 
siderable amount of friction and pressure should necessarily exist. From physical 
reasons, there is also a great probability of the truth of this proposition. The highly 
crystalline structure whieh must necessarily be assigned to the shell’s inner surface, 
combined with the viscidity of the strata of the nucleus in immediate contact with it, 
would evidently, if suffieiently great, tend constantly to equalize the motions of both 
shell and nucleus, and to cause the whole to rotate as one mass. Of the truth of the 
fundamental assumption in artiele 1, I may therefore venture to hope no reasonable 
doubt can exist. 
(6.) The Amount of Elastic Gases given off at the Surface of the Nucleus during 
different Geological Epochs. 
28. If, in the strata of the nucleus, elastic gases were confined by the compression 
of the superior strata, it must follow from Section III. that during the solidification 
of the upper parts of the fluid the rest will tend to expand, and consequently to set 
free the confined gases. If the amount of elastic gases in a cubic unit of any stratum 
be proportional to the pressure to which that stratum is subjected, it must follow 
that the quantity evolved on the solidification of the surface stratum must be pro- 
portional to the amount of contraction of that stratum in solidifying. The expansion 
of the other strata, yet in a fluid state, would also tend to produce an evolution of 
such gases. The evolution of gases from the solidifying stratum would evidently be 
proportional to {\—h)a\, and from any other stratum with the radius a^, proportional 
to the density f of that stratum. But it has been shown in Section III. that in 
general § and (1—^) decrease as a^ decreases; hence we may conclude that the 
amount of elastic gases given off from the surface of the nucleus rapidly decreases 
as the thickness of the shell increases. 
(7.) The Distribution of the Waters on the Surface of the Globe. 
29. The expressions for the variation of gravity obtained in Section II., show that 
if the angular velocity of rotation of the earth remained unchanged, the waters on 
its surface would tend to accumulate towards the equator, by the gradual thickening 
of the shell and the consequent change in the direction of gravity. 
