CHAPTER XXIV. 



WHY DOES ICE FLOAT? 



Nature is full of surprises. By a long 

 series of experimental investigations you 

 think you have established a law that is as un- 

 alterable as those of the Medes and Persians. 

 But once in a while you stumble upon phe- 

 nomena that seem to contradict all that has 

 gone before. 



These, however, may be only the exceptions 

 that prove the rule. It is recognized as a fun- 

 damental law that heat expands and cold con- 

 tracts; that the atom when in a state of in- 

 tense motion (which is the condition produc- 

 ing the effect that we call "heat") requires 

 more room than when its motions are of a less 

 amplitude. In other words, an increase in the 

 amplitude of atomic motion is heating, while 

 a decrease is cooling. It follows from the 

 above statement that the colder a body be- 

 comes the smaller will be its dimensions. 

 There are two or three, and perhaps more, ex- 

 ceptions to this rule, and the most notable one 

 is that of water. Water follows the same law 

 that all other substances do under the action 



