CHAPTER V 



HEAT 



WHEN we go into a room where there is neither 

 sunshine nor a fire, nor anything else to make 

 any part of that room hotter than any other part, 

 we are right in thinking that all the objects in 

 the room must be equally warm. This is ex- 

 pressed by saying that they are all at the same 

 temperature. But if we put a hand on a stone 

 mantelpiece or metal fender it will feel cold to 

 us, while the curtain or carpet will feel quite 

 warm. Again, let us get three basins or jugs 

 and put cold water in one, hot water in another, 

 and warm water in the third. Now if we put 

 one hand in the cold and the other in the hot, 

 and after a while move them both into the warm 

 water, the hand that was in the cold water will 

 feel it warm, and the hand that was in the hot 

 water will feel it cold, although they are now 

 both in the same basin of warm water. We 

 sometimes speak of certain days in the middle 

 of winter as being very warm, whereas if they 

 had come in the middle of summer we should 

 feel them to be very cold. What does all this 

 mean ? Are our senses at fault, or is there any 



(SO 



