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[ti:Recording an Earthquake]
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[00:00.54]Lesson 42
[00:02.45]Recording an earthquake
[00:09.95]What does a pen have to do to record on paper the vibrations generated by an earthquake?
[00:18.95]An earthquake comes like a thief in the night, without warning.
[00:23.69]It was necessary, therefore, to invent instruments that neither slumbered nor slept.
[00:29.84]Some devices were quite simple.
[00:32.36]One, for instance, consisted of rods of various lengths and thicknesses which would stand up on end like ninepins.
[00:41.06]When a shock came, it shook the rigid table upon which these stood.
[00:46.36]If it were gentle, only the more unstable rods fell.
[00:51.17]If it were severe, they all fell.
[00:53.99]Thus the rods, by falling, and by the direction in which they fell,
[00:58.85]recorded for the slumbering scientist the strength of a shock that was too weak to waken him,
[01:05.70]and the direction from which it came.
[01:08.99]But instruments far more delicate than that were needed if any really serious advance was to be made.
[01:15.87]The ideal to be aimed at was to devise an instrument that could record with a pen on paper,
[01:22.77]the movements of the ground or of the table as the quake passed by.
[01:28.24]While I write my pen moves, but the paper keeps still.