EARTHQUAKES

Press, Volume XIII, Issue 1716, 22 August 1868, Page 3

EARTHQUAKES

There exists a very general impression thn earthquakes are preceded and ushered in by some preternatural, and, as it were, expectant calm in the elements, as if to make the confusion and desolation they create the more impressive. The records of such visitations which we possess, however. striking some particular cases of the kind may appear, by no means bear out this as a general f&ct, or go to indicate any particular phase of weather as preferentially accompanying their occurrence. This does not prevent, .howexer, certain conjectures of atmospheric or other circumstances from exercising or determining influence on the time of their occurrence. According to the view we have taken of their origin (viz., the displacement of pressure, resulting in a strain in tie strata at certain points, gradually increasing to the maximum they can bear without disruption,) it is tho last ounce which breaks the camel's back. Great barometical fluctuation, accumulating atmospheric pressure for a time over the sea, and relieving it over the land ; an unusually high tide, aided by long-continued and powerful winds, heaping up the water ; nay, even the tidal action of the sun and moon on the solid portion of the earth's cruet—all these causea, for tho moment combining, may very well suffice to determine the instant oj fracture, when the balance between the opposing forces is on the ovo of subversion. The last mentioned cause may need a few words of explanation. The action of the sun and moon, though it cannot produce a tide in the solid crustTof the earth, tends 'to do so, and were it fluid, would produce it. It, therefore, in point of fact, does bring the solid portions of the earth's surface into a state alternately o stain and compression. The effective part oi their force, in the present case, ia not that which aide to lift or to press the superficial matter—for that, acting alike on the continent and on - the bed of the sea, would have no influence—but that which tenda to produoe lateral displacement; or what geometera call the tangential force. This of necessity brings the whole ring of the earth's surface, which at any instant has the acting luminary on its horizon, into a state of strain ; and the whole area over which it is nearly vertical, into one of compression. We leave this point to be further followed out, but we cannot forbear remarking, that the great volcanic chains of the world have, in point of fact, a direction which this cause of disruption would tend rather to favour than I contravene.— Sir J. Herschell.