EARTHQUAKES IN CENTRAL AMERICA. 821 



retumbos. I estimate the average number of shocks felt annually in 

 Central America at two hundred and fifty. Several conclusions may 

 be drawn from the study of the twenty-three hundred and thirty-two 

 earthquakes that have been registered since the conquest. First, con- 

 trary to the opinion generally prevailing from Chili to Mexico, the 

 tremors occur about alike through the whole year, and not principally 

 at the transitions between the rainy and dry seasons. But, to perceive 

 this clearly, it is necessary to leave out of the account some series of 

 earthquakes that mask the truth, such as that of December, 1879, at 

 San Salvador, in which more than seven hundred shocks occurred in ten 

 days, and which was the prelude to the appearance of a new volcano 

 in the center of Lake Ilopango. With this precaution, a tendency to 

 equality may be observed between the several months, and I am satis- 

 fied that a term of four years will be sufficient to make this equality 

 plain. The same may be said of the retumbos. The maximum of 

 eruptions appears to occur in July. Kluge puts it in August for the 

 whole globe. The coincidence which the same author has predicated 

 between the maxima of aurorje boreales and sun-spots and of volcanic 

 and seismic manifestations has not been historically verified in Central 

 America. The minute study of twenty years of observations at the 

 Institute of Guatemala and my own observations at San Salvador 

 have proved to me that, if the movements of the crust of the earth are 

 connected with those of the barometer, the law of the relation is 

 deeply hidden. I do not deny it, but I have observed nothing analo- 

 gous to what Scrope believes he has established for Stromboli, and 

 Waltershausen for Etna. Earthquakes and retumbos are apparently 

 more frequent at night than in the daytime. I say apparently, because 

 it may be that manifestations, quite perceptible in the stillness of the 

 night, pass unobserved amid the bustle of the day. From what I have 

 seen, I think I can affirm that the signs of terror given by domestic 

 animals are more marked the longer the shock lasts, and that without 

 reference to its intensity. 



While I do not think that it is possible in the present state of 

 knowledge to predict earthquakes, I believe that the phenomena are 

 frequently connected with an indefinable aggregation of atmospheric 

 conditions which, subjected to many years of study, might lead to the 

 discovery of some law. This is so true that persons who have lived 

 long in the country often say when they meet, without knowing why, 

 " There will be an earthquake to-day " ; and they are seldom mistaken. 

 Towns in Central America, situated near active volcanoes, have much 

 less to fear than those which, being in the dangerous zone, are more 

 distant from them. This may be proved by the local history. Guate- 

 mala was destroyed seven times, between 1541 and 1773, while it was 

 near the extinct volcano of Agua ; but it has not suffered since 1775, 

 when it was removed to its present position near the active volcano of 

 Fuego, of -which forty-four eruptions have taken place. Izalco, built 



