

LAWS OF HEAT. WATER. 91 



confidence and hope to our researches for such 

 usefulness in every part of the creation. They 

 have thus a peculiar value in adding connexion 

 and universality to our perception of beneficial 

 design. 



7. There is a peculiar circumstance still to be 

 noticed in the changes from ice to water and from 

 water to steam. These changes take place at a 

 particular and invariable degree of heat ; yet they 

 do not take place suddenly when we increase the 

 heat to this degree. This is a very curious ar- 

 rangement. The temperature makes a stand, as it 

 were, at the point where thaw, and where boiling 

 take place. It is necessary to apply a con- 

 siderable quantity of heat to produce these effects ; 

 all which heat disappears, or becomes latent, as it 

 is called. We cannot raise the temperature of 

 a thawing mass of ice till we have thawed the 

 whole. We cannot raise the temperature of 

 boiling water, or of steam rising from it, till we 

 have converted all the water into steam. Any 

 heat that we apply while these changes are going 

 on is absorbed in producing the changes. 



The consequences of this property of latent 

 heat are very important. It is on this account 

 that the changes now spoken of necessarily 

 occupy a considerable time. Each part in suc- 

 cession must have a proper degree of heat applied 

 to it. If it were otherwise, thaw and evaporation 

 must be instantaneous : at the first touch of 



