Abstract
MEASUREMENTS of earth-movements are of two distinct types. In one type the thing measured is the displacement, or one or more components of the displacement, of a point on the earth's surface. For this purpose the mechanical problem is to obtain a sieady point, to be used as an origin of reference, and this is effected by making use of the resistance which a mass opposes to any change of motion. This may be called the Inertia method of observing earth-movements. It is applicable to ordinary earthquakes, and also to the more minute earth-tremorswhich would pass unnoticed ifinstrumental means of detecting their presence were not employed. The steady point is to be obtained by suspending a heavy mass (with one, two, or three degrees of freedom) in such a manner that its equilibrium is very nearly neutral. Any moderately sudden displacement of the ground in the direction in which the mass has freedom to move leaves the mass almost undisturbed, and the displacement of the ground is therefore easily measured or recorded by a suitable autographic arrangement, which must be so designed as to introduce exceedingly little friction.
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On the Measurement of Movements of the Earth, with Reference to Proposed Earthquake-Observations on Ben Nevis 1 . Nature 33, 68–69 (1885). https://doi.org/10.1038/033068a0
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DOI: https://doi.org/10.1038/033068a0
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