Joseph Priestley (1733-1804) was the scientist who discovered oxygen and other common gases. He was also a dissident clergyman who rejected many Christian doctrines. In 1793 he emigrated to America. With Franklin's encouragement he published an original work in which he summarized the knowledge of electricity to his time and described his own experiments. He anticipated the inverse square law of electrical attraction with his observation that when he electrified a hollow sphere there was no charge inside. He also discovered that charcoal conducts electricity and noted the relationship between electricity andchemical change.