92 Effect of the Momentary Relief of Great Pressure. [May 14, 



vessel must be used. If a pressure vessel of limited size be used and, 

 altering the experiment, if the hermetically sealed glass sphere and the 

 copper sphere with its polar perforations be placed in it separately, then 

 when the pressure is raised to such a point that the glass sphere 

 collapses, the copper sphere will burst outwards. 



I was profoundly impressed at the time by the experiments which I 

 made on board the "Challenger," and I connected them with another 

 experiment which is familiar to chemists. When substances are set to 

 react upon one another in a sealed tube, there is frequently disengage- 

 ment of gas which produces a very high tension in the interior of the 

 tube even when cold. If it is sought to open the tube by breaking off 

 the sealed point, an explosion is almost sure to take place. This may 

 have very serious consequences, and yet it has been produced by a 

 relief of pressure. These examples of the destructive effect which can 

 be produced by the sudden relief of pressure led me to believe that 

 many shocks of earthquake may be due to similar relief of subter- 

 raneous pressure. 



These experiments, whether made with the copper ball or with the 

 brass tube, furnish striking demonstrations of the importance of the 

 element of time in all physical considerations. 



The collapse of the brass tube, under the peculiar circumstances of 

 the experiment, is the exact counterpart of the experiment which is 

 frequently, but unintentionally, made by people out shooting, especially 

 in winter. If, from inattention or other cause, the muzzle of the gun 

 gets stopped with a plug of even the lightest snow, the gun, if fired 

 with this plug in its muzzle, invariably bursts. Light as the plug of 

 snow is, it requires a definite time for a finite pressure, however great, 

 to get it under way. During this short time the tension of the powder 

 gases become? so great that the barrel of the ordinary fowling-piece is 

 unable to withstand it and it bursts. 



