MODEL RELEASED. Physics experiment. Schoolgirl looking at equipment used to test Boyle's Law, one of the Gas Laws. Boyle's Law (first proposed by Robert Boyle in 1662) states that for a fixed mass of gas at a fixed temperature, the product of the pressure and volume should remain constant. This equipment has a sample of gas trapped at the upper end of a tube (left) above a liquid (brown). The scale markings allow the volume of this gas to be measured. The pump (by student's hands) is used to pressurize the liquid and hence compress the gas. The pressure is measured by the gauge (circular, between pump and tube).