5i8 THE POPULAR SCIENCE MONTHLY. 



I have shown by experiment that these supplies may be transmitted 

 through the pores of some kinds of rocks. Simple capillary action, 

 in conjunction with gravity, may force water to penetrate against very 

 strong counter-pressure, from the superficial and cooler regions of the 

 globe, to deep and hot regions, where, by reason of the temperature 

 and pressure it acquires there, it becomes capable of producing very 

 great mechanical and chemical effects. If we suppose that water pene- 

 trates, either directly or after a halt in a reservoir where it has remained 

 liquid, to masses in fusion, so as to acquire there an enormous tension 

 and an explosive force, we shall have the cause of the anterior real ex- 

 plosions and of the instantaneous shocks due to gases at high pressure. 

 If the cavities, instead of forming a single reservoir, are divided into 

 several parts or distinct compartments, there is no reason why the ten- 

 sion of the vapor should be the same in the different receivers, pro- 

 vided they are separated by walls of rock. The pressure may even be 

 very different in two or more of them. This admitted, if a separating 

 wall is broken by excess of pressure or melted by the heat, vapor at 

 high pressure will be set in motion, and in the presence of the solid 

 masses upon which it will strike it will behave just as if there had 

 been an instantaneous formation of vapor, as we supposed in the former 

 case. 



It is very hard to establish, as has been attempted, a clear line of 

 demarkation between the character of the earthquakes of volcanic re- 

 gions proper and of regions without volcanoes, such as Portugal, Asia 

 Minor (Chios, April 3, 1881, five thousand victims), Syria, Algeria, and 

 the rim of the Mediterranean generally. In both classes, the charac- 

 teristic manifestations which we perceive are the same. If, as some 

 assume, the internal movements of the rocks were a cause of real 

 earthquakes, it could only be because those internal movements me- 

 chanically developed heat, and in that way provoked the formation of 

 vapor. But, in the recently disturbed regions we have especially in 

 view, which are the seat of so frequent shocks, another cause is much 

 more probable. There doubtless remain in them interstices and inte- 

 rior cavities that permit the access of water to the hot regions. The 

 depth of the centers of disturbance of earthquakes has been estimated, 

 in different cases, by calculations only grossly approximate, at eleven 

 kilometres, twenty-seven kilometres, and thirty-eight kilometres. In 

 any case, such depth, though very slight in comparison with the length 

 of the radius of the earth, is great enough for the temperature at the 

 normal rate of increase to be very high ; and the same will also be 

 the case with the water that may be present there. Now, as we have 

 already seen, a temperature of 500° C. (900° Fahr.) is sufficient to cause 

 water to explode with violence. 



It is certainly in the largest number of cases very difficult to admit 

 collisions of solid bodies in the interior as the moving causes of earth- 

 quakes. How, for instance, can we conceive that so violent and ex- 



