 John Wilkins had left Oxford with the Restoration of Charles II. The new leader of the Oxford scientific group was Robert Boyle. He was also Locke’s scientific mentor. Boyle (with the help of his astonishing assistant Robert Hooke) built an air pump which led to the formulation of Boyle’s law and devised a barometer as a weather indicator. The work on the air pump led to a controversy with Thomas Hobbes because Boyle’s explanations of the working of the air pump were incompatible with Hobbes’ micro-corpuscular theory. This controversy continued for ten years. Boyle was, however, most influential as a theorist. He was a mechanical philosopher who treated the world as reducible to matter in motion. But he had no micro-corpuscular account of the air.