532 
MR. G. H. DARWIN ON THE PRECESSION OF A VISCOUS SPHEROID, 
that a long time ago it was perhaps a degree greater than at present, and that it was 
then nearly stationary for another long time, and that in still earlier times it was 
considerably less. “ 
The violent changes which some geologists seem to require in geologically recent 
times would still, I think, not follow from the theory of the earth’s viscosity. 
According to the present hypothesis (and for the moment looking forward in time), 
the moon-earth system is, from a dynamical point of view T , continually losing energy 
from the internal tidal friction. One part of this energy turns into potential energy 
of the moon’s position relatively to the earth, and the rest developes heat in the 
interior of the earth. Section 1(3 contains the investigation of the amount which has 
turned to heat between any two epochs. The heat is estimated by the number of 
degrees Fahrenheit, which the lost energy would be sufficient to raise the temperature 
of the whole earth’s mass, if it were all applied at once, and if the earth had the specific 
heat of iron. 
The last column of Table IV., Section 15, gives the numerical results, and it appears 
therefrom that, during the 57 million years embraced by the solution, the energy lost 
suffices to heat the whole earth’s mass 1760° Falrr. 
It would appear at first sight that this large amount of heat, generated internally, 
must seriously interfere with the accuracy of Sir William Thomson’s investigation 
of the secular cooling of the earth ;t but a further consideration of the subject in the 
next paper will show that this cannot be the case. 
There are other consequences of interest to geologists which flow from the present 
hypothesis. As we look at the whole series of changes from the remote past, the 
ellipticity of figure of the earth must have been continually diminishing, and thus the 
polar regions must have been ever rising and the equatorial ones falling; but, as the 
ocean always followed these changes, they might quite well have left no geological 
traces. 
The tides must have been very much more frequent and larger, and accordingly the 
rate of oceanic denudation much accelerated. 
The more rapid alternations of day and night j would probably lead to more sudden 
and violent storms, and the increased rotation of the earth would augment the violence 
of the trade winds, which in their turn would affect oceanic currents. 
Thus there would result an acceleration of geological action. 
The problem, of which the solution has just been discussed, deals with a spheroid.of 
* In my paper “ On the Effects of Geological Changes on the Earth’s Axis,” Phil. Trans. 1877, p. 271, 
I arrived at the conclusion that the obliquity had been unchanged throughout geological history. That 
result was obtained on the hypothesis of the earth’s rigidity, except as regards geological upheavals. The 
result at which 1 now arrive affords a warning that every conclusion must always be read along with the 
postulates on which it is based. 
I ‘ Nat. Phil.,’ Appendix. 
J At the point where the solution stojis there are just 1,300 of the sidereal days of that time in the 
year, instead of 36G as at present. 
