Robert Boyle's second air-pump, an apparatus for experiments on the "spring and weight of air," 1669. Robert Boyle (1627-1691) was a 17th-century natural philosopher, chemist, physicist, and inventor, also noted for his writings in theology. Though his research clearly has its roots in the alchemical tradition, Boyle is largely regarded today as the first modern chemist, and therefore one of the founders of modern chemistry, and one of the pioneers of modern experimental scientific method. Among Boyle's earliest scientific work were studies involving the air pump. The result of this study was the relationship now known as Boyle's law, which states that the pressure and volume of a confined air (gas) are inversely related. Mathematically, this is expressed as pressure times volume equals a constant: PV = constant.