HEAT 



property is the one which always creates the 

 effect we are at present considering. Now there 

 certainly is one property which is found to exist 

 in all the substances like iron which give us 

 extreme feelings of heat or cold. If we put an 

 iron poker in the fire, or still better a brass rod, 

 we shall find that heat gradually creeps along 

 the poker or rod, and parts of it which are not 

 actually in the fire soon become hot. On the 

 other hand we know that it is perfectly easy 

 to hold even a short stick of wood while the 

 end of it is blazing, and if we put several 

 thicknesses of flannel over our hand we can 

 take a very hot kettle off the fire without 

 being burnt. Here, perhaps, we see what is the 

 difference between the two kinds of bodies. 

 Heat can readily pass from one part to another 

 in the iron or brass, while through the wood or 

 flannel it can only creep with great difficulty. 

 This difference is sometimes described by say- 

 ing that iron and brass are good conductors of 

 heat, while wood and flannel are bad conductors. 

 We have now discovered that the substances 

 which feel very hot or cold when touched are 

 good conductors, while those which we can 

 always comfortably hold are bad conductors. 

 If there is really any connexion between these 

 two properties, we may perhaps be able to 

 explain one by help of the other. What will 

 naturally make our finger feel hot ? We shall 

 probably say a rise in its temperature. This 



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