Momentary Relief of Great Pressure 355 



catastrophe of this kind the balance is destroyed, as in the case 

 of air which is transmitting a sound wave. If water I 

 incompressible, it coukl have no tension, however great the 

 pressure to which it might be exposed. What pinched the 

 brass tube was not the column of 2000 or 3000 metres subsiding 

 on it, but the resilience of the unlimited supply of water in it- 

 neighbourhood at the high tension due to its compression by 

 a pressure of 200 or 300 atmospheres. Relatively, this acts 

 instantaneously ; while, to put in motion a mass of water 

 takes a definite time. The quantity of water contained in the 

 brass tube is not sufficient for its resilience to produce any 

 counter-vailing effect to the resilience of the mass of compressed 

 iter outside. 



In the case of the copper sphere it is otherwise. Its diameter 

 is 5 inches, that of the sealed glass bulb inside of it was between 

 i and i i inch, and certainly not greater than lA inch. If we 

 assume it to have been ij inch, then its volume is to that 

 of the copper sphere in the proportion 3* : io 8 = 27 : 1000. 

 If we assume that the glass bulb succumbed at a depth of 5000 

 metres, or at a pressure of 500 atmospheres, then the resilience 

 of the water inside of the copper sphere would have a very 

 considerable effect in neutralising the crushing action of tin- 

 water outside. At the low temperature found at great depth- 

 in the ocean the volume of a mass of distilled water is com- 

 pressed by 2-5 per cent, by a pressure of 500 atmospheres, 

 compressibility of sea-water is nine-tenths of that of 

 di-tilled water, therefore, it would be compressed by 2*25 per 

 The compression produced by a pressure of 500 atmo- 

 spheres is equal to the expansion when the pressure is diminished 



lie same amount. But the volume of the glass bull> 

 not greater than 2-7 per cent. <>! that of the copper sphere, and 

 is probably less; therefore tin- water in the copper sphere 

 would, at the moment of the collapse of the glass -pi 



ery nearlv the volume >t the < <>llap-ed hull), and 

 Copper ball would then be filled, for the moment, with 

 water h ion equal to about atmospheric pres 



Its tension w<>uld then be brought up to 500 atmospheres by 

 ntry of water thn.r. the two poles. 



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