Page:Popular Science Monthly Volume 28.djvu/843

Rh A fact remarked by Humboldt as accompanying the earthquake of the 4th of November, 171)9, at Cumana, was also observed at Guatemala on the 8th of December, 1859. I refer to a sudden and considerable deviation of the magnetic needle, which still continues. To account for it, I propose the theory of a change by the shock in the disposition of the neighboring strata.

A series of more than seven hundred shocks between the 20th and 31st of December, 1879, two of which were disastrous, and which caused much alarm at San Salvador, was the prelude to the appearance, in the neighboring Lake of Ilopango, of a new but ephemeral volcano, whose mass caused the lake to overflow its banks and to produce a terrible inundation in the valley of the Rio Jiboa. The event has been made the subject of a detailed and very interesting study by Messrs. Goodyear and Rockstroh. I will only observe respecting it that two hundred and thirty-seven explosions took place on the 4th of March, 1880, between twenty-five minutes past nine and twenty minutes past ten in the morning, and eight hundred and ninety-seven explosions between eighteen minutes past seven in the evening of the following day and seventeen minutes past three on the next morning.

The retumbos heard at San Salvador and in Colombia on the 27th of August, 1883, were doubtless the echo of the eruption of Krakatoa. I am satisfied that if such a work as I have performed for the small fraction of Central America were done for the whole system of the Cordilleras, from Cape Horn to Behring Strait, and if the different governments would establish meteorologico-seismic observatories, like the one I have directed for four years at San Salvador, it would be possible, in this home of volcanic activity, to form some sound theory of these interesting and terrible phenomena, and perhaps to find some means of announcing them beforehand, as we predict storms on the Atlantic.—Translated for the Popular Science Monthly from the Revue Scientifique.



HE collection of gems exhibited by the National Museum at the Cincinnati and New Orleans Expositions is now on exhibition at the rooms of the Museum in Washington. This much-needed accession, representing a small part of the appropriation for the World's Fair, promises to be one of the most attractive and instructive features of the museum. The large number of visitors who examined the collection, both at the fairs and in its present location, can testify to its interesting character. Although a mere beginning, it is the most complete public collection of gems in the United States. It is contained in two 