Gay-Lussac's law is a gas law which states that the pressure (P) exerted by a gas (of a given mass and kept at a constant volume) varies directly with the absolute temperature of the gas.

T ∝ P     or    P = constant * T

In other words, if an ideal gas is confined in a container whose volume can not be changed, and the temperature is increased, then the pressure should increase proportionally to the temperature.

The apparatus for the experiment is shown above. A temperature sensor and gas sensor are placed inside the glass bulb to measure the pressure and temperature of the gas. Since the glass bulb cannot expand the volume is fixed. The bulb is placed in ice and allowed to cool for a time. When the temperature in the bulb drops the heater is turned on and as the temperature in the bulb rises the temperaure and pressure values ar etaken and graphed. 

If you want to explore the concepts of pressure and temperature try you hand with these online labs / simulations:

Gases Intro

The Gas Laws Simulation

Ideal Gas Law

Gas in a Box