1382 .] 
On the “ Rigid Earth ” Paradox . 651 
form of the sea-surface would not vary. If the bodily tide 
(which is high under the moon) and the sea tide (which is 
low under the moon) were equal , it is plain that no spot of 
sea-surface would be a foot nearer the Earth’s centre at one 
hour than at another. But as we neither do nor can mea- 
sure our high and low waters from the Earth’s centre, but 
only from their own bed, the observable tides would be just 
the same as if the ground had none ; and whether bodily 
tides be greater or less than the oceanic, and synchronous or 
not, the latter will appear the same. Yet both Professors 
repeatedly say (as in “ Phil. Trans.,” 1879, p. 2), “ The only 
terrestrial evidence of the existence of a bodily tide in the 
Earth would be that the ocean tides would be less in height 
than is indicated by theory,” and (p. 30), “ it is only possible 
to judge of the amount of bodily tide by the reduction of the 
ocean tide.” I submit that the detection has never been 
possible this way. The only terrestrial evidence I can see 
possible is in volcanic observations like those of Palmieri. 
But Prof. Darwin, in the only place where he reasons from 
a measured fact, namely, the unexplained residuum of the 
Moon’s acceleration (“ Phil. Trans.,” 1880, p. 481), gets an 
equation (63), of which he says, “ there are obviously two 
solutions ; one of which represents that the Earth is very 
nearly fluid, and the other that it is very nearly rigid. In the 
first case, that of approximate fluidity, . . . the semi-diurnal 
tide [bodily] only lags by the small angle 14'. But this is 
not the solution which is interesting in the case of the 
Earth, for we know that the Earth does not behave ap- 
proximately as a fluid body.” (!) Exactly like Hampden, 
the earth-flattener, with anything he considers to have one 
solution on the theory of roundness. This is not the solu- 
tion for us, says he, for we know the Earth is not round ! 
The remark I should have thought the only natural one 
would be— This exactly agrees with what is found at Vesu- 
vius, high-lava but a minute after the Moon’s transits ; and 
is the only solution interesting us, as we know the Earth 
never has behaved approximately as a rigid body ; and see, 
alike by pendulum experiments, by dislocating dykes, and by 
the almost weekly local earthquakes, — narrowly local 
(by all these far more cogently than by any eruptions), — 
that she behaves in all points as a very nearly perfe< 5 t fluid, 
covered with a scum, and this partly with sea. 
The term “ crust,” applied to the small solid portion, 
is very misleading, and should be scum ; a crust conveying 
inevitably the ideas both of tenacity and some ability of 
dome-like self-support, which are both practically absent. 
2 U 2 
