In examining this table, we must remember that for countries like Peru, Chili, and New Zealand, lying in the southern hemisphere, the records given for the months April to September correspond to the winter months of those countries. The Roman numerals indicate the centuries between which the records date.
| October to March | April to September | |||
|---|---|---|---|---|
| Northern Regions | 1. | Scandinavia and Iceland, xii–xix | 129 | 91 |
2. | British and Northern Isles, xi–xix | 123 | 94 | |
3. | Belgium, France, and Holland, iv–xix | 395 | 272 | |
4. | Rhone Basin, xvi–xix | 115 | 69 | |
5. | Switzerland and Rhine Basin, ix–xix | 327 | 205 | |
6. | Danube Basin, v–xix | 147 | 128 | |
7. | Spanish Peninsula, xi–xiv | 114 | 87 | |
8. | Italy, Sicily, Sardinia, and Malta, iv–xix | 650 | 581 | |
9. | Turco-Hellenic Territory, Syria, Ægean Isles, and Levant, iv–xix | 214 | 222 | |
10. | Northern Zone of Asia, xviii–xix | 46 | 36 | |
11. | Japan (Tokio area), 1872–1880 (small earthquakes) | 213 | 157 | |
12. | Japan b.c. 295-a.d. 1872 (large earthquakes) | 165 | 188 | |
13. | Algeria and Northern Africa | 26 | 20 | |
14. | United States and Canada, xvii–xix | 86 | 48 | |
| Central Regions | 15. | Java, Sumatra, and neighbouring Islands, 1873–4–7–8 | 194 | 182 |
16. | Mexico and Central America, xvi–xix | 26 | 26 | |
17. | West Indies (Mallet), xvi–xix | 108 | 114 | |
18. | West Indies, xvi–xix | 296 | 343 | |
19. | Cuba, xvi–xix | 28 | 23 | |
| Southern Regions | 20. | Chili, and La Plata Basin, xvi–xix | 89 | 89 |
21. | Peru, Columbia, Basin of Amazons, xvi–xix | 506 | 541 | |
22. | New Zealand, 1869–1879 | 166 | 176 | |
Neglecting those records which show as many earthquakes for the winter months as for the summer months, we see at a glance that generally the greater number of shocks have happened during the colder seasons. In the southern hemisphere, so far as the records go, this is not true. In the northern regions, out of fourteen examples there are two exceptions. In the central regions there are two cases where the greatest number of earthquakes have been recorded in the winter months, and two cases where the greatest number have been recorded for the summer.
Altogether, out of twenty-two examples, there are only six exceptions to the rule. These exceptions altogether occur among records many of which are ancient, and are, therefore, more open to error than lists which have been compiled in modern times.
Because small earthquakes are seldom noticed by persons out in the open air, it might be expected that the number of earthquakes observed in warm countries at one portion of the year would be equal to those observed in any other season. Such an argument, however, would hardly apply to most of the records which are quoted, as they refer to destructive disturbances.
If, however, we take the records made in tropical countries from the table just given, we see that in such countries there have been almost as many observations of earthquakes at one season as at any other.
Another fact which might be adduced against the rule that the greater number of earthquakes occur during the winter months would be the comparison of a table of earthquakes recorded previous to the nineteenth century. By doing this we see that for certain countries the winter rule is inverted, and that the greater number of shocks are felt during the summer.
Notwithstanding these objections to Perrey’s conclusions, the balance of evidence is in favour of his general result, and we may conclude that during the colder portions of the year we may expect more shakings than during the warmer portions. Comparing the number of earthquakes of winter and autumn to those of summer and spring, they are to each other in the proportion of 4 : 3.
A fairer way to examine this question, and to determine what is probably the present state of seismic activity in our globe, would be only to consider the earthquakes which have taken place in comparatively recent times, laying especial stress upon those observations which have been made with the assistance of automatic instruments, or those which have been collected by persons interested in these investigations.
For this purpose the following table, showing the distribution of earthquakes in different countries during the nineteenth century, has been compiled.