18 Geological Effects of a Varying Rotation of the Earth. | January, 
To illustrate the efficiency of these different forces, we may re- 
fer briefly to the following calculations: The sinking of the 
equator 110 feet would shorten the time of rotation of the earth 
one minute, or if it was retarded one minute per day, it would 
produce eventually a depression of the equator 110 feet.’ Erich- 
son estimated that if the center of the Mississippi basin were 45° 
55’, and its mouth 29° 8’, the sediment brought down by it 
would retard the earth .00036 of a second in a century. Fer- 
rel, in 1853, assuming that the tide caused by the moon in the 
open sea is two feet in height, and that it is highest two hours 
after the culmination of the moon, showed that it would retard 
the earth at the equator fifty miles in a century.” For the retard- 
ing effect of the sun and moon on a viscous earth, see reference 
above to Darwin’s paper. 
2. A Theoretical View of the Action of these Forces—-We may 
conceive, therefore, the earth rotating in unstable equilibrium 
between these sets of forces. As will be seen presently, any 
change produces effects which tend to counteract the forces 
causing it. If the earth were wholly fluid, only two of the influ- 
ences enumerated would remain, and they are those conceived to 
‘be most efficient now, viz., contraction from loss of heat, and dis- 
‘turbance from the effect of the moon and sun. A varying ellip- 
-ticity would exist, because of the varying distances of the sun and 
moon on the one hand, and the cooling on the other, and there 
would be more or less regularity in this variation of ellipticity as _ 
‘the earth approached or receded from the sun or moon, in the 
movements of revolution. As soon, however, as the earth be- 
came a’solid and rigid mass, as at present, either a decrease Of 
increase of ellipticity would first show itself in the shifting of the 
waters of the ocean, so that the sea-level only would describe the 7 
resulting figure. 
That is, if the earth were nearly perfectly rigid, and the rota- 
tion diminished continually, the sea-level would be continually 
lowering at the equator, and rising at the poles. If, on the other 
hand, by some cause the velocity of rotation were accelerated, the 
waters would rise at the equator and sink at the poles. By a lit 
tle calculation, it will be found that the regions where the sea- 
1 Compare Am, Four. of Sci. (111), XII, p. 353- 
2Newcomb, Reduction and Di:cussions of Observations on the Moon before ns. 
p Il. ae 
