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.[148]
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.
Some remarkable examples of these disturbances are to be found in the records of the great Lisbon earthquake. This earthquake, as a violent movement of the ground, was chiefly felt in Spain, Portugal, northern Italy, the south of France and Germany, northern Africa, Madeira, and other Atlantic islands. In other countries further distant, as, for instance, Great Britain, Holland, Scandinavia, and North America, although the records are numerous, the only phenomena which were particularly observed was the slow oscillations of the waters in lakes, ponds, canals, &c. In some instances the observers especially remark that there was no motion in the soil.
Pebley Dam, in Derbyshire, which is a large body of water covering some thirty acres, commenced to oscillate from the south. A canal near Godalming flowed eight feet over the walk on the north side.
Coniston Water, in Cumberland, which is about five miles long, oscillated for about five minutes, rising a yard up its shores. Near Durham a pond, forty yards long and ten broad, rose and fell about one foot for six or seven minutes. There were four or five ebbs and flows per minute.
Loch Lomond rose and fell through about two and a half feet every five minutes, and all the other lochs in Scotland seem to have been similarly agitated.
At Shirbrun Castle, in Oxfordshire, where the water in some moats and ponds was very carefully observed, it was noticed that the floods began gently, the velocity then increased, till at last with great impetuosity they reached their full height. Here the water remained for a little while, until the ebb commenced, at first gently, but finally with great rapidity. At two extremities of a moat about 100 yards long, it was found that the sinkings and risings were almost simultaneous. The motions in a pond a short distance from the moat were also observed, and it was found that the risings and sinkings of the two did not agree.