STUDIES IN NATURE 



can only be caused by the entry of heat faster 

 than it is carried away. We shall thus look for 

 an explanation from the rate at which heat can 

 enter the finger. If it touches a bad conductor 

 like flannel, some of the heat in the parts of the 

 flannel which were actually in contact with the 

 finger, will enter it, and its temperature will be- 

 gin to rise. But heat cannot travel about the 

 flannel at all easily, so when the heat in the 

 parts touched is used up, very little more from 

 the other parts reaches the finger, and that little 

 will arrive so slowly that it is easily carried 

 away before it can do any harm. On the other 

 hand, if we touch hot iron, heat, not only from 

 the parts we touch, but also from neighbouring 

 regions, rapidly enters our finger, and we receive 

 a vivid, perhaps even a painful, sensation. 

 When the iron is cold, exactly the opposite 

 thing happens. The heat of our finger is quickly 

 conducted away, and a feeling of cold is pro- 

 duced. It is now clear that our sensations of 

 heat and cold are not safe guides in finding the 

 temperature of external objects ; they really tell 

 us at what rate heat is entering or leaving the 

 part of our body which touches the object. 



We now understand why it is foolish to lie 

 or sit long on stone ; it takes so much heat out 

 of us that we feel chilled. We can see why we 

 use blankets and other stuffs made of wool to 

 keep ourselves warm in winter; they do not 

 easily let the heat of our bodies pass away into 



(34) 



