ELECTRICITY 07 



several ounces of iron held up. And if we come to examine 

 this attraction a little more closely, we shall find it presents 

 some other remarkable differences; first of all, one end of 

 this bar (FiG. 37) attracts this key, but the middle does not 

 attract. It is not, then, the whole of the substance which 

 attracts. If I place this little key in the middle it does not 

 adhere ; but if I place it there, a little nearer the end, it does, 

 though feebly. Is it not, then, very curious to find that 

 there is an attractive power at the extremities which is not 

 in the middle to have thus in one bar two places in which 

 this force of attraction resides? If I take this bar and 

 balance it carefully on a point, so that it will be free to 

 move round, I can try what action this piece of iron has 

 on it. Well, it attracts one end, and it also attracts the 

 other end, just as you saw the shellac and the glass did, with 

 the exception of its not attracting in the middle. But if now, 



FIG. 37 FIG. 38 



instead of a piece of iron, I take a magnet, and examine it 

 in a similar way, you see that one of its ends repels the 

 suspended magnet; the force, then, is no longer attraction, 

 but repulsion; but, if I take the other end of the magnet 

 and bring it near, it shows attraction again. 



You will see this better, perhaps, by another kind of ex- 

 periment. Here (FiG. 38) is a little magnet, and I have 

 colored the ends differently, so that you may distinguish one 

 from the other. Now this end (S) of the magnet (FiG. 37) 

 attracts the uncolored end of the little magnet. You see it 

 pulls toward it with great power; and, as I carry it round, 

 the uncolored end still follows. But now, if I gradually bring 

 the middle of the bar magnet opposite the uncolored end of 

 the needle, it has no effect upon it, either of attraction or 

 repulsion, until, as I come to the opposite extremity (N), you 



