HEAT 



the cold air outside. For the same reason, 

 houses built of wood and felt can be made very 

 warm. We see, also, that our hands told us the 

 truth about the basin of warm water. The hand, 

 that had been in the basin of hot water, had 

 taken in a certain amount of extra heat beyond 

 that which it naturally had in common with the 

 other hand and the rest of the body ; it gave 

 some of this out again when it got into the third 

 basin, and, as it was then losing heat, it told us 

 that it felt cold. In the same manner the cold 

 hand was getting heat from the warm water and 

 truthfully told us this. A cold day means to 

 most of us a day that is colder than the ones we 

 have been recently accustomed to, and a hot day, 

 one that is unexpectedly warmer. 



Our feelings about whether things are giving 

 heat to us or taking it from us, whether this is 

 happening quickly or slowly, are wonderfully 

 accurate, and, if we understand what they are 

 telling us, we may safely rely on them. Indeed, 

 we do so in all the ordinary affairs of life. But 

 there are times when it would be neither wise 

 nor indeed possible to do so. It would be 

 foolish and useless to put a hand into a sauce- 

 pan of very hot water to see if it were nearly 

 boiling, for all that our feelings would tell us 

 would probably be that the water was a great 

 deal too hot to be pleasant. Yet this is a thing 

 that we may often want to know, and a little 

 instrument called a thermometer has been made 



(35) 



