ELECTRICITY 71 



electricity is gone at once dispersed on the instant, in a 

 manner wonderful to think of. 



I must now take up a little of your time in showing you 

 the manner in which these powers are transferred from one 

 thing to another; for the manner in which force may be 

 conducted or transmitted is extraordinary, and most essential 

 for us to understand. Let us see in what manner these pow- 

 ers travel from place to place. Both heat and electricity 

 can be conducted; and here is an arrangement I have made 

 to show how the former can travel. It consists of a bar of 

 copper (Fie. 42) ; and if I take a spirit lamp (this is one way 



FIG. 42 



of obtaining the power of heat) and place it under that little 

 chimney, the flame will strike against the bar of copper 

 and keep it 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 dis- 

 tances 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 "'here the 

 wood is, and burn the paper with which I have covered it; 

 but where the metal is beneath, the heat is conducted away 

 too fast for the paper to be burned. And so, if I take a 



