1 903.] prodmcd by the Momentary Relief of Great Pressure. 91 



water. When the water is at rest they are equal. During a catastrophe 

 of this kind the balance is destroyed, as in the case of air which is 

 transmitting a sound wave. If water were incompressible, it could 

 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 its 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 sea water 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 1 and 

 1 J inch, and certainly not greater than 1 J inch. If we assume it to have 

 been 1| inch, then its volume is to that of the copper sphere in the propor- 

 tion 3 3 : 10 3 = 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 the water 

 outside. At the low temperature found at great depths in the ocean 

 the volume of a mass of distilled water is compressed by 2 5 per cent, 

 by a pressure of 500 atmospheres. The compressibility of sea water is 

 nine-tenths of that of distilled water, therefore, it would be compressed 

 by 2 25 per cent. The compression produced by a pressure of 500 

 atmospheres is equal to the expansion when the pressure is diminished 

 by the same amount. But the volume of the glass bulb was not 

 greater than 2'7 per cent, of that of the copper sphere, and it was 

 probably less ; therefore the water in the copper sphere would, at the 

 moment of the collapse of the glass sphere, expand by very nearly the 

 volume of the collapsed bulb, and the copper ball would then be filled, 

 for the moment, with water havins; a tension equal to about atmos- 

 pheric pressure. Its tension would then be brought up to 500 

 atmospheres by the entry of water through the holes at the two poles. 

 The expansion of the mass of compressed water in the copper sphere 

 takes off from the suddenness of the action, while it at the same time 

 reduces, by at least one-half, the difference of pressures outside and 

 inside the sphere at the instant of collapse, and this is the agent which 

 deforms the metal sphere. 



By altering the relation between the volume of the copper sphere 

 and that of the glass sphere enclosed in it and the pressure to which 

 the system is exposed, the effect produced may be varied at will. 

 When experimenting in the sea, the volume of the compressed water 

 outside of the copper sphere is practically infinite. If it is sought 

 to reproduce these effects in the laboratory, then a very large pressure 



