But now we come to another fact. I will take this piece of shell-lac and make it attractive by friction; and remember that whenever we get an attraction of gravity, chemical affinity, adhesion, or electricity (as in this case), the body which attracts is attracted also; and just as much as that ball was attracted by the shell-lac, the shell-lac was attracted by the ball. Now, I will suspend this piece of excited shell-lac in a little paper stirrup, in this way (fig. 33), in order to make it move easily, and I will take another piece of shell-lac, and after rubbing it with flannel, will bring them near together. You will think that they ought to attract each other; but now what happens? It does not attract; on the contrary, it very strongly _repels_, and I can thus drive it round to any extent. These, therefore, repel each other, although they are so strongly attractive--repel each other to the extent of driving this heavy piece of shell-lac round and round in this way. But if I excite this piece of shell-lac, as before, and take this piece of glass and rub it with silk, and then bring them near, what think you will happen? [The Lecturer held the excited glass near the excited shell-lac, 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 anything 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 shew you another experiment which will help to make this clear to you. Suppose I set up this rough indicator again [the excited shell-lac suspended in the stirrup]--it is rough, but delicate enough for my purpose; and suppose I take this other piece of shell-lac, and take away the power, which I can do by drawing it gently through the hand; and suppose I take a piece of flannel (fig. 34), which I have shaped into a cap for it and made dry. I will put this shell-lac into the flannel, and here comes out a very beautiful result. I will rub this shell-lac and the flannel together (which I can do by twisting the shell-lac round), and leave them in contact; and then, if I ask, by bringing them nearer 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 shell-lac 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. [Illustration: Fig. 34.] [Illustration: Fig. 35.]