64 FARADAY 



to any extent. These, therefore, repel each other, although 

 they are so strongly attractive repel each other to the ex- 

 tent of driving this heavy piece of shellac round and round 

 in this way. But if I excite this piece of shellac as before, 

 and take this piece of glass and rub it with silk, and then 

 bring them near, what think you will happen? [The lec- 

 turer held the excited glass near the excited shellac, when 

 they attracted each other strongly.] You see, therefore, 

 what a difference there is between these two attractions; 

 they are actually two kinds of attraction concerned in this 

 case, quite different to any thing we have met with before, 

 but the force is the same. We have here, then, a double 

 attraction a dual attraction or force one attracting and 

 the other repelling. 



Again, to show you another experiment which will help to 

 make this clear to you : Suppose I set up this rough indicator 

 again [the excited shellac suspended in the stirrup] : it is 

 rough, but delicate enough for my purpose; and suppose I 

 take this other piece of shellac, and take away the power, 

 which I can do by drawing it gently through the hand; and 

 suppose I take a piece oi flannel (Fie. 34), which I have 



FIG. 34 



shaped into a cap for it and made dry. I will put this shellac 

 into the flannel, and here comes out a very beautiful result. 

 I will rub this shellac and the flannel together (which I can 

 do by twisting the shellac round), and leave them in contact; 



