"A principle, already well known in the arts, is that many, if not all,
solids may be made to flow like liquids if only adequate pressure be
applied. The making of lead tubes is a well-known practical illustration
of this principle, for these tubes are formed simply by forcing solid
lead by the hydraulic press through a mould which imparts the desired
shape.
"If then a solid can be made to behave like a liquid, even with such
pressures as are within our control, how are we to suppose that the
solids would behave with such pressures as those to which they are
subjected in the interior of the earth? The fact is that the terms solid
and liquid, at least as we understand them, appear to have no physical
meaning with regard to bodies subjected to these stupendous pressures,
and this must be carefully borne in mind when we are discussing the
nature of the interior of the earth."
THE VOLCANO A SAFETY VALVE
Whatever be the state of affairs in the depths of the earth's crust, we
may look upon the volcano as a sort of safety-valve, opening a passage
for the pent-up forces to the surface, and thus relieving the earth from
the terrible effects of the earthquake, through which these imprisoned
powers so often make themselves felt. Without the volcanic vent there
might be no safety for man on the earth's unquiet face.
Professor J. C. Russell, of Michigan University, presents the following
views concerning the status and action of volcanoes:--
"When reduced to its simplest terms, a volcano may be defined as a
tube, or conduit, in the earth's crust, through which the molten rock is
forced to the surface.
Pages:
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248