96 GENERAL SCIENCE 



tors. These are connected by means of pipes with boilers 

 that are often located at considerable distances away. 



It is, however, in the study of Physical Geography, and of 

 Meteorology, that one comes to have some true notion of the 

 vast scale upon which heat is made "latent" in the vaporiza- 

 tion of enormous quantities of water by the sun, and then 

 later set free as this water vapor condenses. These changes 

 are going on everywhere over the earth, but on the largest 

 scale in the tropical regions. Our weather, and the intensity 

 of storms, are both directly related to the heat values in- 

 volved in these changes in the state of water. It will be 

 necessary to keep in mind that other substances than water 

 exhibit like phenomena, and that the value in calories of 

 their heat of fusion and their heat of vaporization varies 

 with the substance. 



SUMMARY 



Heat like other forms of energy can be measured. The units em- 

 ployed for this measurement are the calorie, and the British thermal 

 unit. 



There is a wide variation in the amounts of heat required to melt 

 equal weights of different solids, and to vaporize equal weights of dif- 

 ferent liquids. The heat of fusion for water in the form of ice is 79 

 calories per gram, and for its vaporization from the liquid state is 536 

 calories per gram. 



The heat used in changing water as a liquid into vapor, whether on 

 the stupendous scale of natural vaporization or in steam-heating plants 

 or elsewhere, is wholly set free when condensation of the vapor occurs. 



To continue wearing damp or wet clothing, and to allow it to dry 

 out while being worn, involves the abstraction of much heat from the 

 body. This loss of heat ordinarily can ill be afforded. 



Soils containing water will absorb large amounts of heat with small 

 rise in their temperature. This is by reason of the high specific heat 

 of water. Then, too, by reason of the extremely large value for the 

 heat of vaporization of water, soils that are water soaked are likely to 

 remain cold and unfit for plant growth late into the Spring, and after 

 periods of wet weather. Soils with good drainage warm much more 

 rapidly. 



