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Seis-mom′e-ter.

An instrument for detecting earth quake shocks and recording their duration. The agitation or change of level of a mercurial column sets to work a delicate electric apparatus, which records the time of the first shock, the intervals between the shocks, and the duration of each; their nature, whether vertical or horizontal, the maximum intensity; and, in the case of horizontal shocks, the direction is also shown. The observatory established by the Italian government on the flank of Mount Vesuvius for watching the indications of threatened eruptions is provided with instruments of this class, which are sufficiently sensitive to be affected by any violent shocks occurring in the great Mediterranean basin. On the occasion of a late eruption in the Greek archipelago, Professor Palmieri was enabled to announce that a great disturbance had occurred long before the news of the event had reached Italy. Shocks occasioned by disturbances of Mount Etna are readily observable.

The eruptions are preceded by earthquakes, increasing in intensity and frequency for some days beforehand, and by irregularities in the diurnal variations of the magnetic needle.

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Palmieri (1)
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