826 THE POPULAR SCIENCE MONTHLY. 



port an explanatory hypothesis. The phenomena have heen variously 

 ascribed to subterranean electric storms, to the influence of the sun, 

 supposed to be potent over the interior regimen of the planets as well 

 as upon their course in their orbits ; to thrusts of the liquid or semi- 

 liquid masses of the interior against parts of the solid crusts, which 

 may be caused by the same forces as produce the tides ; to sudden re- 

 ductions of atmospheric pressure ; or to the fall of immense masses of 

 rocks in vast interior cavities. 



Numerous and exact studies, bringing into clear view the relations 

 of earthquakes with the geological structure of the countries subject 

 to them, have given us a better comprehension of their organic causes. 

 An important fact, developed by patient statistical research, is the 

 great inequality in the geographical distribution of the phenomena. 

 There are vast regions in which they are very rare and feeble, and 

 others where the agitations are frequent and often very violent. But 

 it is a significant fact in this connection that the frequency of the dis- 

 turbances is not so much associated with geographical position as with 

 peculiar characters in the constitution of the crust of the earth. Thus, 

 many earthquake regions are characterized by the presence of active 

 volcanoes. A striking example of such association is presented in the 

 narrow tract between the Andes and the Pacific Ocean, in South 

 America, particularly in Colombia, Ecuador, and Chili. " On the 

 coasts of Peru," says A. von Humboldt, " the sky is always clear ; 

 neither hail nor stonns nor fierce lightnings are known ; the subterra- 

 nean thunder attending the earthquake-shocks takes the place of the 

 thunder of the clouds. By long habit and the general opinion that 

 only two or three destructive shocks are likely to occur in a hundred 

 years, the people of Lima are but little more afraid of earthquakes 

 than those of the temperate zones are of hail-storms." In this region, 

 between the sixteenth and twenty-fourth degrees of latitude, there are 

 eighteen volcanoes ; Chili, eminently subject to earthquakes, has thirty- 

 three active volcanoes, between 33 and 43 south. Very different con- 

 ditions prevail east of the Cordilleras, where vast countries like Bra- 

 zil have no earthquakes. Farther north, on the isthmus, there are re- 

 gions where the shocks are so frequent that one of them has been called 

 " Cuscuttan," or the hammock. The single state of Nicaragua has 

 twenty-four volcanoes. Along the coast of Asia is a zone of volca- 

 noes and earthquakes about 9,000 miles long. It begins at Barren 

 Island in the Bay of Bengal, crosses Sumatra, Java, the Moluccas, and 

 the Philippines, bends around by Formosa and the neighboring archi- 

 pelagoes to Japan, and then to the Kurile Islands and Kamchatka, and 

 ends at last in the Aleutian Islands. Through all this zone the volca- 

 noes are numerous and active, and in some parts of it at least, as in 

 Japan and the Philippine Islands, the earth is never at rest. The seis- 

 mograph at Manila is always in motion, even when the ground seems 

 still, and a year never passes without a severe shock. The connection 



