PHYSICAL PARADOXES. 



which preceded it until the whole of the water 

 in the pond became one great block of ice. 



It is easy to see that this would result in 

 the total destruction of the fish, which are at 

 present able to live in the water beneath the 

 ice. Moreover, it would be impossible for men 

 and their cattle to inhabit countries liable to 

 severe winters, because of the lack of water. 

 All the water would be frozen solid, whereas the 

 paradoxical expansion to which it is liable 

 limits the freezing, as we have seen, to the 

 surface, and keeps the water in a fluid state 

 beneath, where it can be got by breaking holes 

 through the ice. 



To the welfare of man and animals, there- 

 fore, this curious irregularity in the expansion 

 of water is a matter of the greatest moment. 



6. Strong Vessel burst by cooling Water in it. 



It has been mentioned already that in the 

 act of freezing water expands to such an extent 

 as to occupy as ice 10 per cent, more space 

 than it occupied as a liquid. This expansion 

 takes place in a very forcible manner, so that 

 even strong iron vessels can be burst by this 

 means. A method of testing this point ex- 

 perimentally, which admits of being worked 

 on a small scale, and easily and repeatedly, is 

 shown in Fig. 32. A strong little steel cylinder, 

 with a central chamber A and a hexagon head B, 



134 



