124 ELECTRICITY. 



hot. Now you are aware that power is being 

 transferred from the flame of that lamp to the 

 copper, and you will see by and by that it is 

 being conducted along the copper from particle 

 to particle; for, inasmuch as I have fastened 

 these wooden balls by a little wax at particular 

 distances from the point where the copper is 

 first heated, first one ball will fall and then the 

 more distant ones, as the heat travels along, 

 and thus you will learn that the heat travels 

 gradually through the copper. You will see 

 that this is a very slow conduction of power as 

 compared with electricity. If I take cylinders 

 of wood and metal, joined together at the ends, 

 and wrap a piece of paper round and then apply 

 the heat of this lamp to the place where the 

 metal and wood join, you will see how the heat 

 will accumulate where the wood is, and burn 

 the paper with which I have covered it; but 

 where the metal is beneath, the heat is con- 

 ducted away too fast for the paper to be burned. 

 And so if I take a piece of wood and a piece of 

 metal joined together, and put it so that the 

 flame shall play equally both upon one and the 

 other, we shall soon find that the metal will 

 become hot before the wood ; for if I put a 



