TIDES, WAVES 99 



against the pressure, but this at last had 

 become too great for the glass to sustain, and 

 the tube had suddenly given way, being 

 crushed by the violence of the action to a fine 

 powder. The collapse had been so rapid and 

 complete that the water had not had time to 

 rush in through the holes at either end of the 

 copper cylinder and thus fill the empty space 

 caused by the collapse of the glass tube, but 

 had instead crushed in the copper wall and 

 thus brought about equilibrium. The pro- 

 cess, which is exactly the reverse of an explo- 

 sion, is called an " implosion." 



During the " Michael Sars " Expedition 

 in 1910 a large number of glass floats wrapped 

 in cloth were sent down to great depths inside 

 a large zinc cylinder : these were all " im- 

 ploded " and reduced to fine white powder, 

 while the cylinder was indented opposite each 

 one of the imploded floats. Some pieces of 

 wood which had been sent down to a great 

 depth attached to a " Challenger " dredge, on 

 being brought up again sank like bricks in 

 a tub of water : all the little cells of the 

 wood had been " imploded " in deep water. 



E^ect of Release of Pressure. — -When water 

 is exposed to great pressure its volume is 

 slightly diminished, and, some heat being 

 liberated, the temperature of the liquid rises. 

 Conversely the volume of a liquid released 



