112 ELECTRICITY. 



Take a watch-glass (or your watch itself will do, 

 you only want something which shall have a 



Fig. 35. 



round face), and now if you place a piece of 

 flat glass upon that, you have a very easily 

 moved centre ; and if I take this lath and put 

 it on the flat glass (you see I am searching for 

 the centre of gravity of this lath, I want to 

 balance it upon the watch-glass), it is very 

 easily moved round, and if I take this piece of 

 sealing-wax and rub it against my coat, and 

 then try whether it is attractive [holding it near 

 the lath], you see how strong the attraction is ; 

 I can even draw it about. Here then you have 

 a very beautiful indicator, for I have with a 

 small piece of sealing-wax and my coat pulled 

 round a plank of that kind, so you need be in 

 no want of indicators to discover the presence 

 of this attraction. There is scarcely a substance 



