Joseph Priestley

Priestley, Joseph (1733–1804), British theologian and chemist. Encouraged and supported by Benjamin Franklin, he wrote The History and Present State of Electricity (1767). His most important discovery was oxygen (1774; named later by Lavoisier), whose properties he investigated. He later discovered many other gases—ammonia, carbon monoxide, hydrogen sulfide— and found that green plants require sunlight and give off oxygen. His association in the 1780s with the Lunar Society brought him into contact with scientists such as James Watt and Erasmus Darwin. Priestley's theological writings and activity led some English Presbyterians into Unitarianism, and he is regarded as a principal architect of the Unitarian church. He was also an opponent of the slave trade and a supporter of the French Revolution. When his house and laboratory were destroyed by people enraged by these ideas, he emigrated to the United States (1794).

See also: Oxygen; Unitarianism.