WILLIAM G. STEVENSON. 201 
are produced which render the earth. unstable—it is said 
that such evisceration causes earthquakes from the 
collapse of the large hollows thus produced. 
Observation, however, does not find the evidence 
which supports this theory to its full extent; and yet 
when we add to the evicerating agencies already men- 
tioned the one yet more powerful and constant in its 
action, viz.: chemical degradation, we are obliged to 
recognize an agency which may at least be sufficient 
to cause seismic shocks of local import. 
Because of the known power exerted by the attractive 
influence of the sun and moon in causing the tides in 
our oceans, some have thought that this same influence 
is sufficient to cause, what may be called, elastic tides in 
the earth’s crust, and also tides in the molten liquid 
within the interior of the earth, which, acting upon the 
earth’s crust, produces fractures and faulting with the 
attendant phenomena of earthquakes. 
Falb elaborated this idea and held that the internal 
fluids were drawn, by the attraction of the sun and 
moon, into cracks and channels which are in the crust 
of the earth, and are therein cooled, or exploded and by 
their explosion cause seismic and volcanic disturbance. 
The attractive force of the moon upon the water on 
our planet is sufficient to ‘‘lift a hemispherical shell 
eight thousand miles in diameter about two or three feet 
higher at its crown than it lifts the earth,” and, from 
the investigations of Lamé, Darwin and Thomson, we 
are asked to believe that this same force is sufficient to 
produce enormous elastic tides. If it be true that the 
interior of the earth is fluid, the elastic tides ‘‘ would be 
sufficient to lift the waters of the ocean up and down so 
that the oceanic tides would be obliterated.’? Such a 
condition does not exist and we are therefore interested 
to know—as a preliminary point in our discussion— 
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