CHAPTER XVI 

 INTRODUCTORY AS TO HEAT: DISCOVERY OF FIRE 



What Is Heat? We know how to measure heat 

 and we know how to feel it. But what is it? 



It is easy to prove that our feeling of heat is not a scien- 

 tific means of measuring it. What seems hot to one per- 

 son may seem cool to another. If you come into a room 

 after a brisk walk on a winter day, it may seem uncom- 

 fortably warm to you, while it may seem uncomfortably 

 cool to a person who has been in it for some time. If 

 you place one hand in hot water and the other in cold, 

 and then transfer both to lukewarm water, the lukewarm 

 water will feel cool to the hand that has been in hot water. 

 After you have been eating ice-cream, does ice-water 

 "taste" as cold as it did before? A piece of wood and a 

 piece of marble may be of just the same temperature, and 

 yet the marble will/ee/ much cooler than the wood. Why 

 is this? 



A little of this sort of thing is quite enough to prove that 

 the feelings of a human being for heat and cold are not a 

 safe guide to the actual facts as to heat and cold. One of 

 the characteristics of science is that it deals with facts 

 rather than feelings. Therefore scientific instruments are 

 needed for recording precisely the facts as to heat and cold. 

 With one of these, the thermometer, you are already familiar. 

 It records the intensity or degree of heat. The degree of 

 heat is called temperature, so, to speak exactly, the ther- 

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