This is charging by induction. What we've got here is an electroscope. In other words, it can tell you if there's any charge around the place. Basically, it's an aluminium rod, and then we've got a little bit of gold foil on it. The reason we've got gold foil on is because it's quite light. It will move if there's a charge, and the charges all over the metal parts and charges like charges repel. So, the other important piece of equipment I've got is a comb, and we need to somehow transfer some charge onto that comb. So, one way of doing it is to just give you hair a brush, and then you bring the comb close to, and you can see that the gold foil is moving upwards. So, what is happening? I've got some charge on my comb. Let's say it's negative. I don't know whether it's negative or positive, but let's say it's negative, and that is making all the negative charge in the top runaway down to the gold leaf and spread out as far away as possible, and so the gold leaf lifts up. Now, if I was to touch the top of the electroscope here, then the electrons can get away, and they'll get away into my finger. So, now they've gone, the gold foil is dropped down, and I've let all the electrons escape from that bottle, or the spare electrons, anyway, there's still plenty of others in there. So, then I'll remove my finger, and the gold leaf will still stay down, and then I'll remove the comb. And the gold leaf magically pops up again, because now it hasn't got enough charge on it, hasn't gone enough of what we were saying with negative charge, and so it's got a surface of positive charges, and again, like charges, repel, and they're trying to get away from each other. And that's charging by induction.