English chemist and amateur natural philosopher whose scientific works covered physics, electricity, magnetism, and optics, in addition to chemistry. The objects of his chemical studies included "fixed air" (carbon dioxide), "nitrous air" (nitric oxide), "marine acid air" (hydrogen chloride), "alkaline air" (ammonia), "vitriolic air" (sulfur dioxide), "phlogisticated nitrous air" (nitrous oxide, laughing gas), and "dephlogisticated air" (oxygen). Priestley was a firm believer in phlogiston. His chemical writings were published in the three volume Experiments and Observations on Different Kinds of Airs (1774- 1777) and in the three volume Experiments and Observations Relating to Various Branches of Natural Philosophie (1779-1786).

Priestley is credited with the discovery of oxygen in 1774, which he produced by focusing sunlight on mercuric oxide. He experimented with dephlogisticated air, noticing that it made himself and animals light-headed. By dissolving fixed air in water, he invented carbonated water. He also noticed that the explosion of inflammable air with common air produced dew. Lavoisier repeated this experiment and took credit for it. Priestley believed in the phlogiston theory, and was convinced that his discovery of oxygen proved it to be correct. He was a politically involved Unitarian preacher and sympathizer with the French Revolution, two facts which forced him and his family to move to America in 1794. At Benjamin Franklin's suggestion, Priestley demonstrated the lack of force inside a charged spherical shell and deduced from this the r^-2 law of electric force. This agreed with the results of John Robinson and was later given the name Coulomb's law in commemoration of Coulomb's independent result.