and the Economy of Fuel. 43 



to be a Non-conductor of Heat. FLAME is also a 

 Non-conductor of Heat. 



THAT heat passes more freely through some bodies 

 than through others, is a fact well known ; but 

 the cause of this difference in the conducting powers 

 of bodies with respect to heat has not yet been dis- 

 covered. 



The utility of giving a wooden handle to a tea-pot or 

 coffee-pot of metal, or of covering its metallic handle 

 with leather, or with wood, is well known. But the dif- 

 ference in the conducting powers of various bodies with 

 regard to heat may be shown by a great number of very 

 simple experiments, such as are in the power of every 

 one to make at all times and in all places, and almost 

 without either trouble or expense. 



If an iron nail and a pin of wood, of the same form 

 and dimensions, be held successively in the flame of a 

 candle, the difference in the conducting powers of the 

 metal and of wood will manifest itself in a manner in 

 which there will be no room left for doubt. As soon as 

 the end of the nail which is exposed in the flame of the 

 candle begins to be heated, the other end of it will grow 

 so hot as to render it impossible to hold it in the hand 

 without being burned ; but the wood may be held any 

 length of time in the same situation without the least 

 inconvenience ; and, even after it has taken fire, it may 

 be held till it is almost entirely consumed, for the unin- 

 flamed wood will not grow hot, and, till the flame actu- 

 ally comes in contact with the fingers, they will not be 

 burned. If a small slip or tube of glass be held in the 

 flame of the candle in the same manner, the end of the 

 glass by which it is held will be found to be more heated 



