CHAPTER XV. BAROMETRICAL FLUCTUATIONS AND EARTHQUAKES--FLUCTUATIONS IN TEMPERATURE AND EARTHQUAKES.

Changes in the barometer and earthquakes.—Mallet, who collected together a number of examples of earthquakes which have occurred with a fall of the barometer, and a number which have happened with a rise, concludes that there are as many instances of the one as of the other. At the great earthquake of Calabria, in 1783, the barometer was very low. The earthquake of the Rhine (February 23, 1828) was preceded by a gradual fall of the barometer, which reached its lowest point upon that day. After the earthquake the barometer again rose. The earthquake of February 22, 1880, in Japan, was accompanied by exactly similar phenomena. Caldcleugh, who observed the heavy shocks in Chili (February 20, 1835), noticed that on February 17 and 18 the barometer fell 5/10 inches. Similar phenomena were observed before the succeeding smaller shocks. After the shocks the barometer again rose. Principal Dawson, speaking of the earthquakes of Canada, observes that some of the shocks have been accompanied with a low barometer.

P. Merian, who examined the connection between the Swiss earthquakes and atmospheric pressure, found that out of twenty-two earthquakes observed in Basle between 1755 and 1836, thirteen of these were local shocks, of which eight were accompanied with sudden changes of pressure. Of the remaining nine, which were only felt slightly in Basle, no change in atmospheric pressure was observed. Of thirty-six earthquakes which, between 1826 and 1836, were felt in Switzerland, thirty were chiefly confined to Switzerland, and ten of these occurred with a low or falling barometer.

Humboldt is of opinion that earthquakes only occur with changes in barometric pressure in those countries where earthquakes are few; and he gives examples where the regular variations of the barometer have gone on without interruption at the time of earthquakes.

Frederick Hoffmann, who examined fifty-seven earthquakes which occurred at Palermo between 1788 and 1838, came to the following result:—

The barometer was sinking	in 20 cases
„ „ rising	in 16 „
„ „ at a minimum	in 7 „
„ „ maximum	in 3 „
„ „ undetermined	in 11 „[114]

The observations of M. S. di Rossi apparently show that the earthquakes in Italy chiefly occur with a barometrical depression and with sudden jumps in atmospheric pressure.

Schmidt, who examined the earthquakes of the Orient, which occurred between 1858 and 1873, says that they were rare with a high barometer, but numerous when the barometer was low.

From an examination of a table of 396 earthquakes (May 8, 1875-Dec. 1881) felt in Tokio, furnished to me by Mr. Arai Ikunosuke, the director of the meteorological department, I obtained the following results:—

The barometer was rising	in 169 cases
„ „ falling	in 154 „
„ „ steady	in 73 „
„ „ below the monthly mean	in 189 „
„ „ above	in 192 „

From this it would appear that in Japan at least the movements of the barometer do not show any marked connection with the occurrence of earthquakes.

When considering this question we must remember the marked effects which a lowering of the barometer produces upon certain volcanoes and solfataras. The volumes of steam emitted from Stromboli and from some of the solfataras in Tuscany hold a marked connection with atmospheric pressure as the quantity of fire damp given off from coal seams—these being greatest when the barometer is low. At certain changes of the weather it is said that the volcano of Vulture, near Melfi, emits noises. These phenomena at once place volcanic phenomena and barometrical pressure in direct relationship.

Changes in temperature.—If, with an earthquake, it should happen that there is a change in the height of the barometer, we should naturally expect that this might be accompanied with the changes in the temperature, in the wind, and in other atmospheric phenomena which are more or less connected with the height of the barometer.

Many times it has been observed that after an earthquake there has been a sudden fall in the temperature. Such was the case with the Yokohama earthquakes of 1880.

Cotte endeavours to show that the earthquakes of Lisbon produced a change upon the temperature of all Europe. In the year which followed this earthquake storms were more common than usual.

Kluge has collected together a large number of examples when there has been a fall of temperature at the time of an earthquake.[115]

At Kiachta, in Siberia, at the time of the earthquake of December 27, 1856, the thermometer fell from 12° to 25° R. We must, however, remember that there are many cases known where the thermometer rose.

M. S. di Rossi remarks that we have the highest records of temperature in the years richest in earthquakes. Thus, in 1873, at the time of the earthquakes in Central and Northern Italy, an abnormal high temperature was remarked. Japanese writers have remarked upon the unusual heat which has shaken their countries. The temperature of subterranean waters have been known to increase before earthquakes.

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