184 matured /HMraclea, 



foot of ice requires as much heat as it would 

 to raise a cubic foot of water 144 degrees Fah- 

 renheit. But, as we have seen, while all of 

 this energy is absorbed as heat, it is not lost as 

 energy. It ceases to be kinetic or active and 

 becomes potential energy. This (let us re- 

 peat) has been called latent heat. The term 

 grew out of the old idea that heat was a fluid 

 and that when it became latent it hid itself 

 away somewhere in the interatomic spaces of 

 matter and ceased to be longer sensible heat. 

 It came into existence in the same manner and 

 occupies the same place in the science of heat 

 that the word " current " does in the science of 

 electricity: both of them are misnomers. 



When the ice is all melted potential energy 

 is no longer stored, but is manifested in the 

 sensible heating of water, the degree of which 

 is measurable by the thermometer, until it 

 reaches the boiling point, where it is again ar- 

 rested. All of the surplus heat above that 

 temperature is consumed in rending the liquid 

 water into moisture globules that float away 

 into the air, each one of them charged with a 

 store of potential energy. Let us follow this 

 vapor spherule as it floats into the upper 

 regions of the atmosphere. Myriads of its 

 fellows travel with it until it reaches a point 

 where condensation takes place, when it col- 

 lapses and unites with other vapor particles to 

 form water again. In doing this the heat that 



