Among Boyle's earliest scientific work were studies involving the air pump. At the time, Robert Hooke was Boyle's laboratory assistant. Starting with the German physicist Otto von Guericke's description of an air pump, Hooke improved on its design, reducing its size and increasing its performance while making it easier to use. Utilizing this improved air pump, Boyle devised experiments to explore the properties of air. He examined the behavior of sound, heat, light, electricity, magnetism, chemical reactions (such as a flame), and living systems (such as small animals or plants) in a vacuum. He also considered the behavior of the air itself under extension or compression. 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.