CHAPTER XVIII 

 HEAT AND COLD 



What Cold Is. Darkness is lack of light. Black, as 

 you may have heard, is not really a color. It is lack of 

 color. Similarly, cold is lack of heat. It is not a positive 

 thing. It is a negative thing. 



Yet we are in the habit of thinking of heat as one thing 

 and of cold as another. We speak of cold as a positive 

 cause of certain effects, when the cause, strictly speaking, 

 is withdrawal of heat. One may say on a cold day that 

 the cold "gets into the house," or "gets into one's bones," 

 when really it is heat that gets out. Ask any one why ice- 

 cream freezes, and he is likely to say that it is "because the 

 cold of the ice gets into the freezer," when really it is be- 

 cause the heat of the cream gets out of the freezer. 



It is not important to correct such inexactness of speech, 

 but it is important to correct an inexactness of ideas which 

 may lie behind such speech. That is, there need be no 

 objection to speaking of cold in the way we do, if we under- 

 stand the real facts involved. Many such inaccurate 

 forms of speech have come into such common and general 

 use that it is practically impossible to correct them. So, 

 in such cases, it is not so important to say what we mean 

 as it is to know what we mean when we say it; the form 

 of speech may be inaccurate, and yet through usage and 

 general understanding, it may have come to convey an 

 accurate meaning. So in this chapter we shall use the word 

 cold when we really mean lack or low amount of heat. 

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