8 2+ THE POPULAR SCIENCE MONTHLY. 



area of a circle of 30, or nearly 2,000 miles radius, or a diameter of 

 one sixth the circumference of the globe. 



The ocean basins are also disturbed, as is proved by the shocks 

 suffered by ships on the deep, without any apparent external cause, 

 and which give an impression as though the vessel were running upon 

 a shoal. The movements of the littoral, also, however slight may be 

 their intensity, are transmitted to the liquid mass. The sea retires 

 from the shore, leaving the bottom dry, sometimes for several miles. 

 Then it returns swiftly upon itself, and, overleaping its normal limit, 

 precipitates itself with fury, and as if in assault, toward the interior of 

 the country, as an enormous wave, which has been frequently known, 

 as in Chili, to reach a height of 100 or 125 feet. Then it retires, car- 

 rying out upon the deep whatever it has gathered up in its passage. 

 This terrible oscillation is repeated three or four times with decreasing 

 energy, unless the movements of the ground persist. These invasions 

 of the sea, or tidal-waves, are often more dreaded by the people, who 

 have had experience of them, than the shocks on land. The huge 

 wave* are also propagated in the ocean to a very great distance from 

 the center of disturbance. Twelve hours after an earthquake that de- 

 stroyed the city of Simoda, Japan, in December, 1854, a formidable 

 wave was precipitated upon the Californian coast, 5,600 miles away. 

 In 1868 a wave of similar origin destroyed Arequipa and Arica, Peru, 

 and ingulfed 30,000 persons. It seemed to have come from Honolulu, 

 in twelve hom*s, or with a speed of 450 miles an hour. The most 

 striking example is that of the wave that followed the Krakatoa ex- 

 plosion, which traveled over a distance of 11,890 miles, or half-way 

 round the globe, in twenty hours and fifty minutes, or at the rate, 

 according to M. Bouquet de la Grye's estimate, of about 900 feet a 

 second. 



Earthquakes may also effect permanent changes in the relief of the 

 land, not only in the shape of crevasses and the overturning of rocks ; 

 slight though appreciable elevations have also .been observed, as in 

 Chili, in 1822, 1835, and 1837. In the last case, marine shells, still alive 

 and adhering to the rocks on which they had grown, appeared above 

 the level of the sea, and served as indisputable witnesses of the change 

 of level which had been suddenly produced. 



Movements of another class are extremely weak, and can not be 

 perceived without the aid of special and delicate instruments. In 

 1869 M. d'Abbadie, examining the surface of a mercurial bath in his 

 observatory at Abbadia, discovered very slight but frequent variations 

 in the situation of the vertical, from which he inferred that the ground 

 is not always motionless, even when it has all the appearances of being 

 so. The same fact has since been confirmed in many places. Abrupt 

 oscillations that have been frequently perceived in the astronomical 

 glasses at the observatory of Pulkowa, and were observed at Nice on 

 the 27th of November, 1884, are also revelations of disturbances in 



