Galileo Thermometer

It's time for another science post.

Seen in the picture above is the Galileo Thermometer. Each one of the coloured'things' in the tube has a little plate, with the temperature engraved on it. You can tell the temperature in the room by looking at the lowest floating indicator, in the picture it's the dark blue one.

So how does it work?
Well, the tube is filled with water, and each one of those glass pieces inside the tube is filled with a mix of water, food colouring and alcohol, the density of the coloured liquid is the same as that of water.
What makes some of the pieces heavier (more dense) than others is the size of the temperature tag. Since objects that are denser sink, and less dense float, this thermometer essentially works according to changes in density.

How does the density change? The density of water changes with temperature, so when the temperature increases, the density of the water decreases and some of those coloured pieces fall down. When the temperature decreases some of the pieces float, and the temperature reading is therefore changed.

This thermometer is quite popular around here, many people have it their offices, but I'm sure that 90% of the people don't know how it works. My description of how it works is compressed. If you didn't get it, and still want to know how it works visit this website http://www.howstuffworks.com/question663.htm