Guericke, Otto von (ôˈtō fən gāˈrĭkə) [key], 1602–86, German physicist, noted for his study of pneumatics. He carried out his most important researches while burgomaster (1646–81) of Magdeburg. In the course of his attempts to create a vacuum he made the first air pump (c.1650). To demonstrate the pressure of air he devised the so-called Magdeburg hemispheres—two hollow copper hemispheres fitted together to form a globe c.14 in. (36 cm) in diameter from which the air could be pumped. A famous woodcut depicts the claim that it required two opposing eight-horse teams to pull the hemispheres apart. He invented (1660) a machine to generate electricity from the friction of the hand held against a rotating sulfur ball; he also predicted the periodicity of comets.