Читать книгу The Romance of Modern Geology. Describing in simple but exact language the making of the earth with some account of prehistoric animal life онлайн

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If a very tall jelly is allowed to stand for some time, or if the table on which it stands is shaken a good deal, then, as we know, rifts will sometimes appear in the jelly. The reason for these breakdowns in the jelly's composition is that owing to the distribution of its weight it is always in what we call a state of strain; and it is sometimes not strong enough to support this strain, and, almost without apparent cause, will sometimes give way. Much more solid bodies than jelly act in the same way. The great bridge near Quebec which collapsed in 1907 was to all appearance quite sound and strong; but there were strains in the iron girders, and without warning these strains suddenly produced rifts in the iron and steel framework and it broke down. Similarly the towers of churches and cathedrals, which are built on arches, will give away quite suddenly after standing to all appearance quite firm for hundreds of years. There is an architect's maxim which runs, "The arch never sleeps." That means that the arches on which the great weight of a church or cathedral tower rests are always in a state of strain; they are always, as it were, imperceptibly quivering; and they are always liable, if the strain on them should be increased in the slightest degree, to give way, or to resettle the weight on their shoulders in some way.