As a consequence of this he predicts an increase of earthquakes in the years 1886, 1891, 1898, 1900, &c.[104]
Dr. E. Naumann, who critically examined the large earthquakes of Japan, showed that there was an approximate coincidence between many of the disturbances and the thirty-three year period of meteoric showers.[105]
Humboldt states that a great shower of meteors was seen at Quito before the great earthquake of Riobamba (Feb. 4, 1797). The earthquakes of 1766 and 1799 at Cumana are also said to have been accompanied with meteoric showers. Mallet gives a list of large earthquakes which occurred at the times when meteors were observed.[106]
The hours at which earthquakes are most frequent.—From the examination of a catalogue of over 2,000 earthquakes which occurred in various parts of the world between the years 1850 and 1857, made by Kluge, it is found that both for the northern and southern hemispheres the observations which were made during the night generally exceed those which were made during the day.
| Number of Earthquakes | ||
|---|---|---|
| Day | Night | |
| In the Northern Hemisphere | 938 | 1592 |
| In the Southern Hemisphere | 292 | 357 |
In the northern hemisphere the greatest number were observed between 10 p.m. and 12 p.m. (360 shocks), and the fewest between 12 and 2 p.m. (139 shocks). In the southern hemisphere, the greatest number were observed at night between 12 and 1, and the smallest number between 1 and 2 and 4 and 5 in the afternoon.[107] These distinctions, however, are less distinctly marked as we approach the Equator. Schmidt found for the earthquakes of the Orient between 1774 and 1873, that shocks had been most frequent about half-past two a.m., and less frequent about 1 p.m. With regard to these conclusions, which have been reached with much labour, we might be inclined to think that they are partially to be explained on the supposition that more observations are made during the night than during the day—the personal experience of residents in an earthquake country being, that many earthquakes which occur during the day are passed by unnoticed, whilst those which occur during the night are recorded by thousands of observers. Such a view is certainly confirmed by the instrumental records obtained in Japan. From 1872 to 1880 inclusive there were 261 shocks recorded, 132 of which occurred between the hours of 6 p.m. and 6 a.m.
Earthquakes and sun spots.—Of late years considerable attention has been drawn to a coincidence between the occurrence of sun spots, magnetic disturbances, rainfall, and other natural phenomena.
These periods of sun spots occur about every eleven years, and appear to be coincident with the periodical return of the planet Jupiter. In Japan, Dr. E. Naumann sought for a coincidence between these periods of sun spots and earthquakes, but without any marked results.
Schmidt, who carefully compared his lists of earthquakes with the appearance of sun spots, came to the conclusion that there was no marked coincidence. The occurrence of earthquakes had sometimes synchronised with sun spots, whilst at other times there had been a maximum of sun spots and no earthquakes.
M. R. Wolf[108] apparently considers that earthquakes, like volcanic eruptions and the appearance of the aurora, are coincident with sun spots.