Boyle, Charles and Gay-Lussac are immortal in chemical lore because they discovered experimentally--in three consecutive centuries--the laws of gases. In 1622, Boyle discovered that if the temperature remains constant, the product of the pressure and the volume remains constant, or In modern terms: for constant temperature, pressure and volume are inversely proportional--if one goes up, the other goes down. In 1787, Charles reveled that when the pressure is constant, the volume and temperature are proportional--if one goes up, so does the other. In 1809, Gay-Lussac showed that whenever the volume is constant, the pressure on the walls of a container of gas is proportional to the temperature.
The fundamental gas law (also known as the ideal gas law) incorporates Boyle's law, Charles's law and Gay-Lussac's law into one equation: PV = nRT. In this equation, P is pressure, V is volume, n is the number of gas molecules, R is a constant that depends on what units are being used and T is the temperature (in degrees Kelvin). Put your fingertip over the T to get Boyle's law: "If temperature is constant, the product of the pressure and the volume is a constant." similarly, you can get Charles's law by covering the P, and Gay-Lussac's law by covering the V. The ideal gas law gives the relationship between pressure, volume and temperature for n moles of a gas. If the gas is unconfined, the pressure goes to zero and the volume expands infinitely.
Dalton's Law states the the total pressure of a mixture of gases is the sum of the pressures of the individual gases. Avogadro's law says that the volume of a gas is proportional to the number of moles of the gas. Henry's law reveals that, at a constant temperature, the amount of gas that is dissolved in a liquid is proportional to the partial pressure of the gas in the container. Graham's law shows that the rate that a gas diffuses in inversely proportional to the density of the gas.