HEAT, ELECTRICITY, AND CHEMICAL ACTION. 143 



tery see what heat we get (fig. 48). Is not that 

 beautiful? it is a complete bridge of power. 

 There is metallic connection all the way round 

 in this arrangement, and where I have inserted 

 the platinum, which offers some resistance to 

 the passage of the force, you see what an amount 

 of heat is evolved, this is the heat which the 

 zinc would give if burnt in oxygen, but as it is 

 being burnt in the voltaic battery it is giving it 

 out at this spot. I will now shorten this wire 

 for the sake of showing you that the shorter 

 the obstructing wire is, the more and more 

 intense is the heat, until at last our platinum 

 is fused and falls down, breaking off the circuit. 

 Here is another instance. I will take a piece 

 of the metal silver, and place it on charcoal con- 

 nected with one end of the battery, and lower 

 the other charcoal pole on to it. See how bril- 

 liantly it burns (fig. 49). Here is a piece of 

 iron on the charcoal, see what a combustion is 

 going on; and we might go on in this way 

 burning almost everything we place between the 

 poles. Now I want to show you that this 

 power is still chemical affinity that if we call 

 the power which is evolved at this point heat, or 

 electricity, or any other name referring to its 



