Look around you! People and objects look larger when they are nearby and smaller when they are far away.

How large should a figure be in the scene below if he is standing on the red line? Look at the other people and buildings for clues.

He should be taller than the man at the back, but shorter than the man at the front of the picture.

Knowing that a person who is further away in a painting should look smaller is helpful. But it wasn't enough for Leonardo da Vinci. He wanted to know why distant objects looked smaller and what size to paint them if he knew exactly how far away they were. In his notebooks he wrote and sketched his ideas about why distant objects always look smaller. He also described his experiments for measuring the apparent sizes of objects at different distances.

The Classroom Activity: How Far? How Small? describes how to conduct an experiment similar to Leonardo's with very simple materials. Try it to discover for yourself the relationship between size and distance.