456 THE POPULAR SCIENCE MONTHLY. 



cially along the lines of unequal density where the continents join the 

 ocean-beds. 



The quantity of lava that a volcano emits during an eruption sur- 

 passes anything we can imagine. The volume of the lava-stream of 

 Kilauea, in the great eruption of 1840, was estimated at five and a half 

 milliards of cubic metres, and a still larger mass was thrown out in 

 1855 from the crater at the summit of Mauna Loa, of which Kilauea 

 is the smaller outlet. But these are trifling compared with the mass 

 of matter emitted by the Iceland volcano of Skapta-Jokull, in 1783, 

 which was estimated to equal the volume of Mont Blanc, or not less 

 than five hundred milliards of cubic metres ! According to the prob- 

 ably exaggerated estimate of Zollinger, the total volume of scoriae and 

 ashes thrown out in 1815 from a volcano in the island of Sumbawa 

 (Tomboro), to the distance of five hundred kilometres, equaled twice 

 that of Mont Blanc. We have more exact data concerning the erup- 

 tion of Coseguina, a small volcano of Central America, which, in 1835, 

 rained pumice-stone on the land and sea over a radius of fifteen hun- 

 dred kilometres, and discharged daily not less than fifty milliards of 

 cubic metres. When we consider the stupendous force required to 

 raise and throw to a distance such volumes of matter, it is difficult 

 to believe that the underground forces that feed the volcanoes, and 

 which we know have been active from a very remote period, are mere 

 accumulations of matter in fusion. Still more difficult is it to suppose 

 that the heat of these fires is due to chemical action developed in the 

 bosom of the earth. We can not but seek, in the wide-spread, incan- 

 descent mass under the thin crust that varies, possibly, from twenty to 

 one hundred kilometres in thickness, the proximate cause of volcanic 

 phenomena. The objection based on the non-coincidence of eruptions 

 of volcanoes situated in the same region disappears when the mechan- 

 ism of the eruption is explained by the more or less fortuitous depo- 

 sition of infiltrated water. 



The question appears to be reduced to deciding whether the central 

 nucleus on which the mass of lava rests is itself liquid or whether it is 

 solid. This is a much disputed point, and great ingenuity has been 

 shown on both sides of the argument. The hypothesis of a liquid 

 nucleus has long been favored, and it has many adherents. It has been 

 objected that a liquid nucleus would be subject to tides that would 

 break in an instant the thin envelope and produce terrific cataclysms. 

 Ampere, in particular, felt it impossible to reconcile this consequence 

 of the hypothesis with the calm that reigns on the surface. " Those 

 who maintain the idea of a liquid nucleus," said he, " do not appear 

 to have considered the effect of the moon's attraction on this enor- 

 mous liquid mass, which would cause tides analogous to those of our 

 seas, but far more terrible, by reason of their extent and the density 

 of the liquid. It is difficult to conceive how the earth's crust could 

 withstand the action of a kind of hydraulic lever 1,400 leagues long." 



