PHYSICAL PARADOXES. 



frozen solid. Take out the tube, dip it a few 

 seconds in ordinary cold water, to melt the 

 surface of the ice, which will be frozen fast to 

 the tube and corks, then remove the corks, and 

 push out the bar of ice. To get it out of the 

 test-tube easily, a hole must be broken through 

 the glass at the bottom, to allow air to enter 

 as the bar of ice leaves. Fix the bar of ice 

 horizontally by one end in a strong clamp on 

 a retort stand. Or a round hole of the right 

 size in an upright piece of wood will do very 

 well. 



Hang a weight of, say, seven pounds from 

 the free end of the bar of ice by a fine wire, like 

 that used by florists for wiring flowers, in such 

 a way that the weight is two inches clear of the 

 table. If the bar of ice be one inch thick, and 

 the wire be one-hundredth of an inch, the 

 weight of seven pounds rests upon a part of 

 the ice whose area is the hundredth part of a 

 square inch. That is a weight of 700 pounds, 

 or nearly one- third of a ton, to the square inch 

 a very heavy pressure indeed. 



Now we have seen that pressure alone can 

 melt ice. Accordingly the pressure of the 

 wire melts the ice immediately beneath it, so 

 that it gradually cuts its way through as com- 

 pletely as a grocer cuts through a cheese by 

 drawing a wire through it ; but it takes a few 

 minutes for the wire to cut through the ice. 



But when the bar has been cut right through, 

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