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[ti:Recording an Earthquake]
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[00:01.47]Lesson 42
[00:03.45]Recording an earthquake
[00:11.47]What does a pen have to do to record on paper the vibrations generated by an earthquake?
[00:19.70]An earthquake comes like a thief in the night, without warning.
[00:24.83]It was necessary, therefore, to invent instruments that neither slumbered nor slept.
[00:31.38]Some devices were quite simple.
[00:33.83]One, for instance, consisted of rods of various lengths and thicknesses which would stand up on end like ninepins.
[00:41.76]When a shock came, it shook the rigid table upon which these stood.
[00:47.32]If it were gentle, only the more unstable rods fell.
[00:51.64]If it were severe, they all fell.
[00:54.65]Thus the rods, by falling, and by the direction in which they fell,
[00:59.67]recorded for the slumbering scientist the strength of a shock that was too weak to waken him,
[01:05.62]and the direction from which it came.
[01:09.39]But instruments far more delicate than that were needed if any really serious advance was to be made.
[01:17.67]The ideal to be aimed at was to devise an instrument that could record with a pen on paper,
[01:24.33]the movements of the ground or of the table as the quake passed by.
[01:29.99]While I write my pen moves, but the paper keeps still.