What do you think of when you hear the name René Descartes? Most folks know him as a philosopher, but Descartes was also one of the best scientists of his day.

Descartes' name, in fact, is associated these days with a simple experiment you can do at home. It's called a Cartesian Diver.

Cartesian Diver Experiment

To make your own Cartesian diver, all you'll need is a big plastic bottle you can see through, like an empty soda bottle, one of the liter-sized ones. You also need an eye dropper.

First, pull all the labels and stuff off the bottle so you can see into it easily, and fill it up with water. Next, fill the eye-dropper with some water too but not all the way! You want just enough water inside the dropper so that when you place it inside the bottle, it floats with just a little of the squeeze bulb out of the water.

Hover

Once you have the eye-dropper floating at the top of the bottle, put the cap on tight. Now you're ready to go! Just squeeze the sides of the bottle and you'll find that the water-dropper descends! Stop squeezing and it rises up again. With a little practice you can even make it hover midway.

Can you figure out why the Cartesian diver goes up and down when you squeeze the sides of the bottle? For the answer, tune in next time.