ELECTRICITY 65 



and then if I ask, by bringing them near our indicator, what 

 is the attractive force? it is nothing; but if I take them apart, 

 and then ask what will they do when they are separated? 

 why, the shellac is strongly repelled, as it was before, but 

 the cap is strongly attractive; and yet, if I bring them both 

 together again, there is no attraction; it has all disappeared 

 [the experiment was repeated]. Those two bodies, therefore, 

 still contain this attractive power ; when they were parted, it 

 was evident to your senses that they had it, though they do 

 not attract when they are together. 



This, then, is sufficient, in the outset, to give you an idea of 

 the nature of the force which we call ELECTRICITY. 

 There is no end to the things from which you can evolve this 

 power. When you go home, take a stick of sealing-wax I 

 have rather a large stick, but a smaller one will do and 

 make an indicator of this sort (Fie. 35). Take a watch- 

 glass (or your watch itself will do; you only want some- 



FIG. 35 



thing which shall have a 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 

 which we may not use. Here are some indicators (FiG. 36). 

 I bend round a strip of paper into a hoop, and we have as 

 HC VOL. xxx c 



