When Leonardo watched the movement of water as it passed through a narrow channel, he noticed that some of the water became caught up in swirling patterns, called vortices. Being a very clever boy, he was then able to make the connection between the behaviour of the water as it flowed through the narrow channel and the way that blood flows as it passes through a heart valve.

Figuring out that he was looking at pretty much the same thing, he reasoned that the swirling vortices created by the movement of the blood though the valve would eventually cause the valve to close up – until the next beat of the heart pushed the valve open and the whole process began again.

Even though he couldn’t easily see the movement of air, he drew the same effect around the edge of a wing. But you don’t have to take to the skies to watch this. Next time you see leaves (or litter) blowing around the edge of a building, take a close look and see if you can spot the vortices that will be revealed in the circular movement of the leaves.