CONDUCTION OF ELECTKICITY. 125 



piece of phosphorus on the wood, and another 

 piece on the copper, you will find that the 

 phosphorus on the copper will take fire before 

 that on the wood is melted ; and this shows you 

 how badly the wood conducts heat. But with 

 regard to the travelling of electricity from place 

 to place its rapidity is astonishing. I will, first 

 of all, take these pieces of glass and metal, and 

 you will soon understand how it is that the 

 glass does not lose the power which it acquired 

 when it is rubbed by the silk ; by one or two 

 experiments I will show you. If I take this 

 piece of brass and bring it near the machine, 

 you see how the electricity leaves the latter and 

 passes to the brass cylinder. And again, if I 

 take a rod of metal and touch the machine with 

 it I lower the indicator, but when I touch it 

 with a rod of glass no power is drawn away, 

 showing you that the electricity is conducted by 

 the glass and the metal in a manner entirely 

 different ; and to make you see that more 

 clearly we will take one of our Leyden jars. 

 Now, I must not embarrass your minds with 

 this subject too much, but if I take a piece of 

 metal and bring it against the knob at the top 

 and the metallic coating at the bottom, you will 



