This was on May 10 (April 28), 1877. The complete period was about
20 seconds, the amplitude being 1·5″ and 2″. One hour and fourteen
minutes before this he observes that there had been a severe earthquake
at Iquique, the distance to which in a straight line was 10,600
kilomètres, and on an arc of a great circle, 12,500 kilomètres.
On September 20 (8), in 1867, Mr. Wagner had observed at Pulkova
oscillations of 3″, seven minutes before which there had been an
earthquake at Malta. On April 4 (March 23), 1868, an agitation of the
level had been observed by Mr. Gromadzki, five minutes before which
there had been an earthquake in Turkestan. Similar observations had
been made twice before. These, however, had not been connected with any
earthquakes—at least, Mr. Darwin remarks—with certainty.
_Phenomena analogous to the pendulum and level observations._—As
examples of phenomena which are analogous to those made on pendulums
and levels, the following may be noticed. On March 20, 1881, at 9 P.M.
a watchmaker in Buenos Ayres observed that all his clocks oscillating
north and south suddenly began to increase their amplitude, until some
of them became twice as great as before. Similar observations were
made in all the other shops. No motion of the earth was detected.
Subsequently it was learnt that this corresponded with an earthquake in
Santiago and Mendoza.[146]
Another remarkable example illustrating the like phenomena is furnished
by the observations which were made on December 21, 1860, by means of a
barometer in San Francisco, which oscillated, with periods of rest, for
half an hour. No shock was felt, nor is it likely that it was a local
accident, as it could not be produced artificially. On the following
day, however, a violent earthquake was experienced at Santiago.[147]
At the time or shortly after the great Lisbon earthquake, curious
phenomena were observed in distant countries, which only appear to be
explicable on the assumption of the existence of earth pulsations.
Thus at Amsterdam and other towns, chandeliers in churches were
observed to swing. At Haarlem water was thrown over the sides of tubs,
and it is expressly mentioned that no motion was perceived in the
ground.
At the Hague a tallow chandler was surprised at the clashing noise
made by his candles, and this the more so because no motion was felt
underfoot.
_Unusual disturbances in bodies of water._—At the time of large
earthquakes it would appear that earth pulsations are produced, which
exhibit themselves in countries where the actual shaking of the
earthquake is not felt, by disturbances in bodies of waters like lakes
and seas.
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