Boyle’s law states that the pressure of a gas multiplied by its volume is a constant, constant, as long as the amount of gas and the temperature are kept the same.
In other words, if you decrease the volume of a gas, its pressure increases. It is this increased pressure that produces the spring of the air. You can feel this effect using a bicycle pump by covering the end with a finger and pushing the handle in.
Although it bears his name, this law was first proposed not by Boyle, but by English scientists Richard Towneley and Henry Power, who performed a series of experiments with a Torricelli barometer and published their results in 1663.
Boyle saw an early draft of the book and discussed the results with Towneley. He confirmed them by experiment and published “Mr Towneley’s hypothesis” in 1662 as part of a response to criticism of his original experiments.