HISTORY OF ATOMS

THE EXPERIMENTS
BOYLE'S LAW
If a gas has a constant mass and is held at a constant temperature, then the product of its pressure and volume are a constant value.

Boyle's Law relationship between pressure and temperature

Boyle's Law relationship between pressure and temperature

To see this animation please visit the NASA website.

So this law says that if I am holding a gas at a constant temperature and a constant mass, then by increase the pressure of the gas, the volume of the gas will decrease and vise versa. This makes sense qualitatively because pressure is related to force. So if I push down on something "flexible" like a gas I will squish it, as a result it will occupy less volume.