No. 23. [From Nature, August I, 1872, Vol. vi. pp. 260, 261.] 



VOLCANOES AND EARTHQUAKES 



IT is generally admitted that an earthquake is due to the 

 passing of a sensible wave through the earth's crust. It has 

 also been observed that the occurrence of earthquakes is 

 frequently associated with eruptions from volcanic vents, 

 usually in the neighbourhood, but not unfrequently at con- 

 siderable distances. It is evident and it has struck nearly 

 all observers that there must be some connection between 

 the two classes of phenomena. The nature of this connection 

 has been differently explained by different writers. But the 

 purpose of this note is not to criticise existing theories, but to 

 propose one, which I believe to be new, and to be capable of 

 explaining why a sudden volcanic eruption must ordinarily be 

 accompanied by earthquake shocks of greater or less violence 

 (not necessarily always sensible), and why earthquakes may 

 occur without any contemporaneous outburst. 



In the preface of his Physikalische Geologic Bischof suggests 

 that the phenomena observed in the laboratory should be taken 

 as our guide to explain what happens in nature. Let us see, 

 then, if in the laboratory we meet with any phenomena analo- 

 gous to volcanoes and earthquakes. 



When a reaction has to be performed in a sealed tube, and 

 it is expected that much gas will be evolved, and consequently 

 the pressure in the tube be much increased, it is one of the 

 commonest precautions to draw out the tube to a capillary 

 orifice before closing it. When this precaution has been 

 neglected, and even although the point be allowed to blow itself 

 out in the flame of a lamp, an explosion not unfrequently 

 attends the attempt to open it. Let us consider the circum- 

 stances. 



We have a tube whose walls are being pushed out by a very 

 high pressure from within, which, however, it resists; but at 

 the moment that this pressure is suddenly relieved at one 

 point, the tube bursts. What is the cause of the explosion? 



