Okay, this is a Galilean thermometer. It's a very good demonstration of buoyancy. What we have is a column of water with lots of little beads into it in it. Those beads all have exactly the same volume. And we know that the buoyant force on each one of them is equal to the weight of the water displaced. So each one of those having the same volume it will have a slightly different density. So the upward force is going to be the same on each one of them. But the downward force will be slightly different. So the more dense ones will have a higher downward force than the less dense ones. As the density of the water changes, the downward force on some will be greater than the upward force of buoyancy and so they will sink. So the most dense ones at the moment are at the bottom. The least dense ones are at the top. And if the temperature changes, you will find that they will either drop down. If the water becomes less dense, the temperature becomes higher. Or they will rise up. If the water becomes more dense, and the temperature becomes a little bit lower. Now if you hang onto the water, you may be able to change the density by raising it slightly. Because what I am doing is warming the water up. And so the water is now less dense than that. And so for the same volume, we have got less buoyant force, but we have got the same weight force. And so the balance of the forces is causing our mass to accelerate. I will bake very slowly downwards. And the water down the bottom is cool. So we have got a bit of a temperature inversion. This is then a really good example of buoyancy.