Joseph Priestley (March 26,1733 – February 8, 1804) was an eighteenth-century British natural philosopher, Dissenting clergyman, political theorist, theologian, and educator. He is usually credited with the discovery of oxygen gas, although Carl Wilhelm Scheele and Antoine Lavoisier also have such a claim.

A member of marginalized religious groups throughout his life, Priestley advocated religious toleration and equal rights for religious Dissenters. He argued for the extension of civil rights, because he believed that individuals could bring about progress and eventually the Christian Millennium. In his metaphysical works, Priestley attempted to combine theism, materialism, and determinism, a project that has been called "audacious and original". The controversial nature of these works combined with Priestley's outspoken support of the French Revolution aroused public and governmental suspicion; he was eventually forced to flee to the United States after a mob burned down his home and church in 1791.

Priestley made significant contributions to pedagogy, including the publication of a seminal work on English grammar, the promotion of a liberal arts curriculum, and the advocacy of the study of modern history.

During his lifetime, Priestley's scientific reputation rested on his invention of soda water, his writings on electricity, and his discovery of several "airs" (gases), the most famous being what Priestley dubbed "dephlogisticated air" (oxygen). However, Priestley's determination to reject Lavoisier's "new chemistry" and to cling to the phlogiston theory of heat eventually left him isolated within the scientific community. Priestley's science was never divorced from his theology, and he consistently tried to fuse Enlightenment rationalism with Christian theism. <div style="clear:both;"></div>

Priestley was born to an established Dissenting family (i.e., they did not conform to the Church of England) in West Yorkshire. He was the oldest of the six children born to Mary Swift and Jonas Priestley, a finisher of cloth. To ease his mother's burdens, Priestley was sent to live with his grandfather around the age of one; after his mother died five years later, he returned home. When his father remarried in 1741, Priestley was sent to live with his aunt and uncle, the wealthy and childless Sarah and John Keighley. Because Priestley was precocious—at the age of four he could flawlessly recite all 107 questions and answers of the Westminster Shorter Catechism—she sought the best education for the boy, intending him for the ministry. During his youth, Priestley attended local schools where he learned Greek, Latin, and Hebrew.

Around 1749 Priestley became seriously ill and believed he was dying. Raised as a devout Calvinist, he believed a conversion experience was necessary for salvation, but doubted he had had one. This emotional distress eventually led him to question his theological upbringing, causing him to reject election and to accept universal salvation. As a result, the elders of his home church refused him admission as a full member.

Priestley's illness left him with a permanent stutter and he gave up any thoughts of entering the ministry. In preparation for joining a relative in trade in Lisbon, he studied French, Italian, and German in addition to Chaldean, Syrian, and Arabic. He was tutored by the Rev. George Haggerstone, who first introduced him to higher mathematics, natural philosophy, logic, and metaphysics through the works of Isaac Watts, Willem 's Gravesande, and John Locke.

Priestley eventually decided to return to his theological studies, and in 1752 matriculated at Daventry, a Dissenting academy. Because he had already read widely, Priestley was allowed to skip the first two years of coursework. He continued his intense study; this, together with the liberal atmosphere of the school, shifted his theology further leftward and he became a Rational Dissenter. Abhorring dogma and religious mysticism, Rational Dissenters emphasized the rational analysis of the natural world and the Bible.

Priestley later wrote that the book which influenced him the most, save the Bible, was David Hartley's Observations on Man (1749). Hartley's psychological, philosophical, and theological treatise postulated a material theory of mind. Hartley aimed to construct a Christian philosophy in which both religious and moral "facts" could be scientifically proven, a goal which would occupy Priestley for his entire life. In his third year at Daventry, Priestley committed himself to the ministry, what he described as "the noblest of all professions".

Priestley's major modern biographer, Robert Schofield, describes his first "call" in 1755 to the Dissenting parish in Needham Market, Suffolk as a "mistake" for both Priestley and the congregation. Priestley yearned for urban life and theological debate and Needham Market was a small, rural town with a congregation wedded to tradition. Attendance and donations dropped sharply when they discovered the extent of his heterodoxy. While Priestley's aunt had promised her support if he became a minister, she refused any further assistance when she realized he was no longer a Calvinist. In order to earn extra money, Priestley proposed opening a school, but local families informed him that they would refuse to send their children. He also presented a series of scientific lectures titled "Use of the Globes", which was more successful.

Priestley's Daventry friends helped him obtain another position in Nantwich, Cheshire; his time there was happier. The congregation cared less about Priestley's heterodoxy and he opened a school. Unlike many schoolmasters of the time, Priestley taught his students natural philosophy and even bought scientific instruments for them. Appalled at the quality of the available English grammars, Priestley wrote his own: The Rudiments of English Grammar (1761). His innovations in the description of English grammar, particularly his efforts to disassociate it from Latin grammar, have led twentieth-century scholars to describe him as "one of the great grammarians of his time". After the publication of Rudiments and the success of Priestley's school, Warrington Academy offered him a teaching position in 1761. <div style="clear:both;"></div>

In 1761 Priestley moved to Warrington and assumed the post of tutor of modern languages and rhetoric at the town's Dissenting academy, although he would have preferred to teach mathematics and natural philosophy. He fit in well at Warrington and quickly made friends. On 23 June 1762 he married Mary Wilkinson of Wrexham. Of his marriage, Priestley wrote:

This proved a very suitable and happy connexion, my wife being a woman of an excellent understanding, much improved by reading, of great fortitude and strength of mind, and of a temper in the highest degree affectionate and generous; feeling strongly for others, and little for herself. Also, greatly excelling in every thing relating to household affairs, she entirely relieved me of all concern of that kind, which allowed me to give all my time to the prosecution of my studies, and the other duties of my station.

On 17 April 1763 they had a daughter, whom they named Sarah after Priestley's aunt.

All of the books Priestley published while at Warrington emphasized the study of history; Priestley considered it essential for worldly success as well as religious growth. He wrote histories of science and Christianity in an effort to reveal the progress of humanity and, paradoxically, the loss of a pure, "primitive Christianity".



In his Essay on a Course of Liberal Education for Civil and Active Life (1765), Priestley argued that the education of the young should anticipate their future practical needs. This principle of utility guided his unconventional curricular choices for Warrington's aspiring middle-class students. He recommended modern languages instead of classical languages and modern rather than ancient history. Furthermore, because Priestley viewed education as one of the primary forces shaping a person's character and the basis of morality, he, unusually for the time, promoted the education of middle-class women. Some scholars of education have described Priestley as the most important English writer on education between the seventeenth-century John Locke and the nineteenth-century Herbert Spencer.

In his Lectures on History and General Policy (1788), Priestley encouraged the study of modern history, rarely studied at the time. The lectures cover a wide array of topics—everything from forms of government to commerce to manners. He narrated a providentialist and naturalist account of history, arguing that the study of history furthered the comprehension of God's natural laws. His millennial perspective was closely tied to his optimism regarding scientific progress and the improvement of humanity. He believed that each age would improve upon the previous and the study of history allowed people to see and further this progress. Priestley also presented a new method for historical research that emphasized the primacy of original documents and material objects. Lectures on History was well-received and was employed by many educational institutions, such as New College at Hackney, Brown, Princeton, Yale, and Cambridge. Priestley also designed two Charts to serve as visual study aides for his Lectures on History. Both were popular for decades and the trustees of Warrington were so impressed with Priestley's lectures and charts that they arranged for the University of Edinburgh to grant him a Doctor of Law degree in 1764.

The intellectually stimulating atmosphere of Warrington, referred to during the eighteenth century as the "Athens of the North", increased Priestley's interest in natural philosophy. He gave lectures on anatomy and, with his friend John Seddon, performed experiments regarding temperature. Despite his busy teaching schedule, Priestley wrote a history of electricity. Friends introduced him to the major experimenters in the field in Britain—John Canton, William Watson, and the visiting Benjamin Franklin—who encouraged Priestley to perform the experiments he wanted to include in his history. In the process of replicating others' experiments, Priestley became intrigued by unanswered questions and was prompted to undertake experiments of his own design. (Impressed with the manuscript of his history of electricity and his Charts, Canton, Franklin, Watson, and Richard Price nominated Priestley for a fellowship in the Royal Society; he was accepted in 1766.)

In 1767, the 700-page The History and Present State of Electricity was published to positive reviews. The first half of the text is a history of the study of electricity to 1766; the second and more influential half is a description of contemporary theories about electricity and suggestions for future research. Priestley reported some of his own discoveries in the second section, such as the conductivity of charcoal and other substances, and the continuum between conductors and non-conductors. This discovery overturned what he described as "one of the earliest and universally received maxims of electricity", that only water and metals could conduct electricity. Such experiments demonstrated Priestley's early and ongoing interest in the relationship between chemistry and electricity. Based on experiments with charged spheres, Priestley was also the first to propose that electrical force followed an inverse-square law, although he did not generalize or elaborate on this.

Priestley's strength as a natural philosopher was qualitative rather than quantitative and his observation of "a current of real air" between two electrified points would later interest Michael Faraday and James Clerk Maxwell as they investigated electromagnetism. Priestley's text became the standard history of electricity for over a century; Alessandro Volta (who later invented the battery), William Herschel (who discovered infrared radiation), and Henry Cavendish (who discovered hydrogen) all relied upon it. Priestley wrote a popular version of the History of Electricity for the general public titled A Familiar Introduction to the Study of Electricity (1768).

In 1767, the Priestleys moved from Warrington to Leeds and Priestley became Mill Hill Chapel's minister. Two sons were born to the Priestleys in Leeds: Joseph, Jr. on 24 July 1768 and William three years later. Theophilus Lindsey, a rector at Catterick, Yorkshire, became one of Priestley's few friends in Leeds: "I never chose to publish any thing of moment relating to theology, without consulting him". Although Priestley had extended family around Leeds, it does not appear that they communicated. Schofield conjectures that they considered him a heretic. Each year Priestley traveled to London to consult with his close friend and publisher, Joseph Johnson, and to attend meetings of the Royal Society.

When Priestley became its minister, Mill Hill Chapel was one of the oldest and most respected Dissenting congregations in England; however, during the early eighteenth century the congregation had fractured along doctrinal lines, and the Methodist movement was luring away Dissenters. Priestley believed that by educating the young, he could strengthen the bonds of the congregation.

While Priestley outlined these theories of religious education in his Institutes of Natural and Revealed Religion (1772–74), he more importantly outlined his belief in Socinianism. The doctrines he laid out would become the standards for Unitarians in Britain. This work marked an important change in Priestley's theological thinking that is critical to understanding his later writings—it paved the way for his materialism and necessitarianism (the belief that a divine being acts in accordance with necessary metaphysical laws).

Priestley's major argument in the Institutes is that the only revealed religious truths that can be accepted are those that match one's experience of the natural world. Because his views of religion were deeply tied to his understanding of nature, the text's theism rests on the argument from design. The Institutes shocked and appalled many readers, primarily because it challenged basic Christian orthodoxies, such as the divinity of Christ and the miracle of the Virgin Birth. Methodists in Leeds penned a hymn asking God to "the Unitarian fiend expel / And chase his doctrine back to Hell." Priestley wanted to return Christianity to its "primitive" or "pure" form by eliminating the "corruptions" which had accumulated over the centuries. The fourth part of the Institutes, An History of the Corruptions of Christianity, became so long that he was forced to issue it separately. Priestley believed that the Corruptions was "the most valuable" work he ever published. In demanding that his readers apply the logic of the emerging sciences and comparative history to the Bible and Christianity, he alienated religious and scientific readers alike—scientific readers did not appreciate seeing science used in the defense of religion and religious readers dismissed the application of science to religion.

Priestley engaged in numerous political and religious pamphlet wars. According to Schofield, "he entered each controversy with a cheerful conviction that he was right, while most of his opponents were convinced, from the outset, that he was willfully and maliciously wrong. He was able, then, to contrast his sweet reasonableness to their personal rancor." However, as Schofield points out, Priestley rarely altered his opinion as a result of these debates. While at Leeds he wrote controversial pamphlets on the Lord's Supper and on Calvinist doctrine; thousands of copies were published, making them some of Priestley's most widely-read works.

Priestley also founded the Theological Repository in 1768, a journal committed to the open and rational inquiry of theological questions. Although he promised to print any contribution, only like-minded authors ever submitted articles. He was therefore obliged to provide much of the journal's content himself (this material became the basis for much of his later theological and metaphysical works). After only a few years, due to a lack of funds, he was forced to cease publishing the journal. He revived it in 1784, with similar results.

Many of Priestley's political writings supported the repeal of the Test and Corporation Acts, which restricted the rights of Dissenters. They could not hold political office, serve in the armed forces, or attend Oxford and Cambridge unless they subscribed to the Thirty-nine Articles of the Church of England. Dissenters repeatedly petitioned Parliament to repeal the Acts, arguing that they were being treated as second-class citizens.

Priestley's friends, particularly other Rational Dissenters, urged him to publish a work on the injustices experienced by Dissenters; the result was his Essay on the First Principles of Government (1768). An early work of modern liberal political theory and Priestley's most thorough treatment of political theory, it—unusually for the time—precisely distinguishes between political and civil rights and argues for expansive civil rights. Priestley identifies separate private and public spheres, contending that the government should only have control over the public sphere. Education and religion, in particular, he maintains, are matters of private conscience and should not be administered by the state. Priestley's later radicalism emerged from his belief that the British government was infringing upon these individual freedoms. Essay on Government went through three English editions and was translated into Dutch.

Priestley also defended the rights of Dissenters against the attacks of William Blackstone, an eminent legal theorist, whose Commentaries on the Laws of England was becoming the standard legal guide. Blackstone's book stated that dissent from the Church of England was a crime and that Dissenters could not be loyal subjects. Furious, Priestley lashed out with his Remarks on Dr. Blackstone's Commentaries (1769), correcting Blackstone's grammar (a highly politicized subject at the time), his history, and his interpretation of the law. Blackstone, chastened, altered subsequent editions of his Commentaries: he rephrased the offending passages and removed the sections claiming that Dissenters could not be loyal subjects, but he retained his description of Dissent as a crime.

Although Priestley claimed that natural philosophy was only a hobby for him, he clearly took it seriously. In his History of Electricity he describes the scientist as promoting the "security and happiness of mankind". Priestley's science was always eminently practical and he rarely concerned himself with theoretical questions—his model was Benjamin Franklin. When he moved to Leeds, Priestley continued his electrical and chemical experiments (the latter aided by a steady supply of carbon dioxide from a neighboring brewery). Between 1767 and 1770, he presented five papers to the Royal Society from these initial experiments; the first four papers explored coronal discharges and other phenomena related to electrical discharge, while the fifth reported on the conductivity of charcoals from different sources. His subsequent experimental work focused on chemistry and pneumatics.

Priestley published the first volume of his projected history of experimental philosophy, The History and Present State of Discoveries Relating to Vision, Light and Colours (referred to as his Optics), in 1772. Priestley paid careful attention to the history of optics and presented excellent explanations of early optics experiments, but his mathematical deficiencies caused him to dismiss several important contemporary theories. Furthermore, he did not include any of the practical sections that had made his History of Electricity so useful to practicing natural philosophers. Unlike his History of Electricity, it was not popular and had only one edition, although it was the only English book on the topic for 150 years. The text was hastily written and it sold poorly; the cost of researching, writing, and publishing the Optics convinced Priestley to abandon his history of experimental philosophy.

Priestley was considered for the position of astronomer on James Cook's second voyage to the South Seas, but was not chosen. Still, he contributed in a small way to the voyage: he provided the crew with a method for making soda water, which he erroneously speculated might be a cure for scurvy. He then published a pamphlet with Directions for Impregnating Water with Fixed Air (1772). Priestley did not exploit the commercial potential of soda water, but others such as J. J. Schweppe made fortunes from it. In 1773, the Royal Society recognized Priestley's achievements in natural philosophy by awarding him the Copley Medal.

Priestley's friends wanted to find him a more financially secure position, and in 1772, prompted by Richard Price and Benjamin Franklin, Lord Shelburne wrote to Priestley asking him to direct the education of his children and to act as his general assistant. Reluctant to sacrifice his ministry, he nevertheless accepted the position, resigned from Mill Hill Chapel on 20 December 1772, and preached his last sermon on 16 May 1773.

In 1773, the Priestleys moved to Calne and a year later Lord Shelburne and Priestley took a tour of Europe. According to Priestley's close friend Theophilus Lindsey, Priestley was "much improved by this view of mankind at large". Upon their return, Priestley easily fulfilled his duties as librarian and tutor. The workload was intentionally light, allowing him time to pursue his scientific investigations and theological interests (Shelburne even equipped a laboratory for him in Bowood House). Priestley also became a political adviser to Shelburne, gathering information on parliamentary issues and serving as a liaison between Shelburne and the Dissenting and American interests. When the Priestleys' third son was born on 24 May 1777, they named him Henry at the Lord's request.

Priestley wrote his most important philosophical works during his years with Lord Shelburne. In a series of major metaphysical works published between 1774 and 1780—An Examination of Dr. Reid's Inquiry into the Human Mind (1774), Hartley's Theory of the Human Mind on the Principle of the Association of Ideas (1775), Philosophical Necessity (1775), Disquisitions relating to Matter and Spirit (1777), The Doctrine of Philosophical Necessity Illustrated (1777), and Letters to a Philosophical Unbeliever (1780)—he argues for a philosophy which foregrounds four concepts: determinism, materialism, causation, and necessity. By studying the natural world, he argued, people would learn how to become more compassionate, happy, and prosperous.

Strongly suggesting that there is no mind-body duality, Priestley puts forth a materialist philosophy in these works, that is, one founded on the principle that everything in the universe is made of matter that we can perceive. However, he simultaneously contends that discussing the soul is impossible because it is made of a divine substance, and humanity cannot access the divine. Despite his separation of the divine from the mortal, this position shocked and angered many of his readers, who believed that such a duality was necessary for the soul to exist.

Responding to Baron d'Holbach's Système de la Nature and David Hume's Dialogues Concerning Natural Religion (1779) as well as the French philosophes, Priestley maintained that materialism and determinism could be reconciled with a belief in God. He criticizes those whose faith is shaped by books and fashion, drawing an analogy between the skepticism of educated men and the credulity of the masses.

Maintaining that humans had no free will, Priestley was the first to claim that what he called "philosophical necessity" (a position akin to absolute determinism) is consonant with Christianity, a position based on his understanding of the natural world. Like the rest of nature, man's mind is subject to the laws of causation, Priestley contends, but because a benevolent God created these laws, the world and the people in it will eventually be perfected. Evil is therefore only an imperfect understanding of the world. Priestley believed that mankind could be perfected through a study of nature.

When Priestley's friend from Leeds, Theophilus Lindsey, decided to establish a new Christian denomination that would not restrict its members' beliefs, Priestley and others such as publisher Joseph Johnson hurried to his aid. On 17 April 1774, Lindsey held the first Unitarian service in Britain; he had even designed his own liturgy, of which many were critical. Priestley rushed to his defense with Letter to a Layman, on the Subject of the Rev. Mr. Lindsey's Proposal for a Reformed English Church (1774), claiming that only the form of worship had been altered, not its substance, and attacking those who only followed religion as a fashion. Priestley attended the church regularly in the 1770s and occasionally preached there. He continued to support institutionalized Unitarianism for the rest of his life, writing several Defenses of Unitarianism and encouraging the foundation of new Unitarian chapels throughout Britain and the United States.

Priestley's years in Calne were the only ones in his life dominated by scientific investigations, and the most scientifically fruitful. His experiments were almost entirely confined to "airs", and out of this work emerged his most important scientific texts: the six volumes of Experiments and Observations on Different Kinds of Air (1774–86). These experiments helped repudiate the last vestiges of the theory of four elements, which Priestley attempted to replace with his own variation of phlogiston theory. Priestley's work on "airs" is not easily classified. As historian of science Simon Schaffer points out, it "has been seen as a branch of physics, or chemistry, or natural philosophy, or some highly idiosyncratic version of Priestley's own invention". Furthermore, the volumes were both a scientific and a political enterprise for Priestley; he argues in them that science could destroy "undue and usurped authority", writing that the government has "reason to tremble even at an air pump or an electrical machine".

Priestley's first volume of Experiments and Observations on Different Kinds of Air outlined several important discoveries, namely, experiments that would eventually lead to the discovery of photosynthesis and the discovery of several airs: "nitrous air" (nitric oxide, NO), "vapor of spirit of salt" (later called "acid air" or "marine acid air"; anhydrous hydrochloric acid, HCl), "alkaline air" (ammonia, NH₃), "diminished" or "dephlogisticated nitrous air" (nitrous oxide, N₂O), and "deplogisticated air" (oxygen, O₂). Priestley also developed the "nitrous air test", which tested for the "goodness of air". Using a pneumatic trough, he would mix nitrous air with a test sample, over water or mercury, and measure the decrease in volume—the principle of eudiometry. After a small history of the study of airs, he explained his own experiments in an open and sincere style; as Thorpe writes, "whatever he knows or thinks he tells: doubts, perplexities, blunders are set down with the most refreshing candour." Priestley also invented and described cheap and easy-to-assemble experimental apparatus. His colleagues therefore believed that they could easily reproduce his experiments in order to verify them or to answer the questions that had puzzled him.

Although many of his results puzzled him, Priestley used phlogiston theory to resolve the difficulties. This, however, led him to conclude that that there were only three types of "air": "fixed", "alkaline", and "acid". Priestley ignored the burgeoning chemistry of his day, indeed dismissing it in these volumes. Instead, he focused on gases and the "changes in their sensible properties", as had natural philosophers before him. He isolated carbon monoxide (CO) but seems not to have realized that it was a separate "air" from the others that he had discovered.

After the publication of the first volume of Experiments and Observations, Priestley undertook another set of experiments. In August 1774 he isolated an "air" that appeared to be completely new, but he did not have an opportunity to pursue the matter because he was about to tour Europe with Shelburne. While in Paris, however, Priestley managed to replicate the experiment for others, including Antoine Lavoisier. After returning to Britain in January 1775, he continued his experiments and discovered "vitriolic acid air" (sulfur dioxide, SO₂). In March he wrote to several people regarding the new "air" that he had discovered in August. One of these letters was read aloud to the Royal Society, and a paper outlining the discovery, titled "An Account of further Discoveries in Air", was published in Philosophical Transactions. Priestley called the new substance "dephlogisticated air"; he first tested it on mice, who surprised him by surviving quite a while entrapped with the air, and then on himself, writing that it was "five or six times better than common air for the purpose of respiration, inflammation, and, I believe, every other use of common atmospherical air". He had discovered oxygen gas (O₂).

Priestley assembled his oxygen paper and several others into a second volume of Experiments and Observations on Air, published in 1776. He does not emphasize his discovery of "dephlogisticated air" (leaving it to Part III of the volume) but instead argues in the preface how important such discoveries are to rational religion. His paper narrates the discovery chronologically, relating the long delays between experiments and his initial puzzlements; thus, it is difficult to determine when exactly Priestley "discovered" oxygen. Such dating is significant as both Lavoisier and Swedish pharmacist Carl Wilhelm Scheele have strong claims to the discovery of oxygen as well, Scheele having been the first to isolate the gas (although he published after Priestley) and Lavoisier having been the first to describe it as purified "air itself entire without alteration" (not "dephlogisticated air").



In his paper "Observations on Respiration and the Use of the Blood", Priestley was the first to suggest a connection between blood and air, although he did so using phlogiston theory. In typical Priestley fashion, he prefaced the paper with a history of the study of respiration. A year later, clearly influenced by Priestley, Lavoisier was also discussing respiration at the Académie des sciences. His work began the long train of discovery that produced papers on oxygen respiration and culminated in the overthrow of phlogiston theory.

Around 1779 Priestley and Shelburne had a rupture, the reasons for which remain unclear. Shelburne blamed Priestley's health, and Priestley claimed Shelburne had no further use for him. Some contemporaries speculated that Priestley's outspokenness had hurt Shelburne's political career. Schofield argues that the most likely reason was Shelburne's recent marriage to Louisa Fitzpatrick—apparently, she did not like the Priestleys. Although Priestley considered moving to America, he eventually accepted Birmingham New Meeting's offer to be their minister.

In 1780 the Priestleys moved to Birmingham and spent a happy decade surrounded by old friends, until they were forced to flee in 1791 by mob violence. Priestley accepted the ministerial position at New Meeting on the condition that he be required to preach and teach only on Sundays, so that he would have time for his writing and scientific experiments. As in Leeds, Priestley established classes for the youth of his parish and by 1781, he was teaching 150 students. Although New Meeting supplied Priestley with an annual salary of 100 guineas, such a sum would never have supported his experimental interests. Happily, friends and patrons frequently offered him money and goods that allowed him to continue his scientific investigations.

Many of the friends that Priestley made in Birmingham were members of the Lunar Society, a group of manufacturers, inventors, and natural philosophers who assembled monthly to discuss their work. Matthew Boulton (manufacturer), Erasmus Darwin (naturalist, physician, poet, and grandfather to Charles Darwin), James Keir (chemist and geologist), James Watt (inventor and engineer), Josiah Wedgwood (manufacturer) and William Withering (botanist, chemist, and geologist) formed the core of the group. Priestley was asked to join this unique society and contributed much to the work of its members. In this stimulating intellectual environment, he published several important scientific papers. One of the most significant was "Experiments relating to Phlogiston, and the seeming Conversion of Water into Air" (1783). The first part of the paper attempts to refute Lavoisier's challenges to his work on oxygen; the second part describes how the steam that results from heated water is "converted" into air. After several variations of the experiment, with different substances as the fuel for the fire and several different collecting apparatuses which produced different results, he concluded that air could travel through more substances than previously surmised, a conclusion "contrary to all the known principles of hydrostatics". This discovery, along with his earlier work on what would later be recognized as gaseous diffusion, would eventually lead John Dalton and Thomas Graham to formulate the kinetic theory of gases.



In 1777, Antoine Lavoisier had published Réflexions sur le Phlogistique pour servir de Développement à la Théorie de la Combustion et de la Respiration, the first of what proved to be a series of attacks on phlogiston theory; it was against these attacks that Priestley responded in 1783. While Priestley accepted parts of Lavoisier's theory, he was unprepared to assent to the major revolutions Lavoisier proposed—the overthrow of phlogiston, a chemistry conceptualized around elements and compounds, and a new chemical nomenclature. It was Priestley's original experiments on "dephlogisticated air" (oxygen), combustion, and water that provided Lavoisier with the data he needed to construct much of his system, but Priestley never accepted Lavoisier's new theories and continued to cling to phlogiston theory for the rest of his life. Lavoisier's system was based largely on the weight of substances and Priestley was less interested in these measurements; he preferred to observe changes in heat, color, and particularly volume. His experiments tested "airs" for "their solubility in water, their power of supporting or extinguishing flame, whether they were respirable, how they behaved with acid and alkaline air, and with nitric oxide and inflammable air, and lastly how they were affected by the electric spark."

By 1789, when Lavoisier published his Traité élémentaire de chimie and founded the Annales de Chimie, the new chemistry had come into its own. Priestley published several more scientific papers in Birmingham, the majority attempting to refute Lavoisier; Priestley and other Lunar Society members argued that the new French system was too expensive, too difficult to test, and unnecessarily complex. Priestley in particular rejected its "establishment" aura. Priestley's refusal to accept Lavoisier's "new chemistry" and his determination to adhere to a less satisfactory theory has confused many scholars. Schofield explains it thus: "Priestley was never a chemist; in a modern, and even a Lavoisian, sense, he was never a scientist. He was a natural philosopher, concerned with the economy of nature and obsessed with an idea of unity, in theology and in nature. He attempted, prematurely, to conflate phenomena and give reasons for the reactions he observed." Historian of science John McEvoy largely agrees, writing that Priestley's view that nature was coextensive with God and thus infinite, a view which encouraged him to focus on facts over hypotheses and theories, prompted him to reject Lavoisier's system. Moreover, he argues that "Priestley's isolated and lonely opposition to the oxygen theory was a measure of his passionate concern for the principles of intellectual freedom, epistemic equality and critical inquiry." Priestley himself claimed in the last volume of Experiments and Observations that his most valuable works were his theological ones because they were "superior [in] dignity and importance". Priestley, unlike his friends in the Lunar Society, would continue the war over phlogiston until he died.

Although Priestley was busy defending phlogiston theory from the "new chemists", most of what he published in Birmingham was theological. In 1782 he published the fourth volume of his Institutes, An History of the Corruptions of Christianity, describing how he thought the teachings of the early Christian church had been "corrupted" or distorted. Schofield describes the work as "derivative, disorganized, wordy, and repetitive, detailed, exhaustive, and devastatingly argued". The text addresses issues from the divinity of Christ to the proper form for the Lord's Supper. Thomas Jefferson would later write of the profound effect that Corruptions had on him: "I have read his Corruptions of Christianity, and Early Opinions of Jesus, over and over again; and I rest on them … as the basis of my own faith. These writings have never been answered." Although a few readers such as Jefferson and other Rational Dissenters approved of the work, it was generally harshly reviewed because of its extreme theological positions, particularly its rejection of the Trinity.

In 1785, while Priestley was engaged in a pamphlet war over his Corruptions, he also published The Importance and Extent of Free Enquiry, claiming that the Reformation had not really reformed the church. In words that would boil over into a national debate, he challenged his readers to enact change:

Let us not, therefore, be discouraged, though, for the present, we should see no great number of churches professedly unitarian…. We are, as it were, laying gunpowder, grain by grain, under the old building of error and superstition, which a single spark may hereafter inflame, so as to produce an instantaneous explosion; in consequence of which that edifice, the erection of which has been the work of ages, may be overturned in a moment, and so effectually as that the same foundation can never be built upon again…. And till things are properly ripe for such a revolution, it would be absurd to expect it, and in vain to attempt it.

Although discouraged by friends from using such inflammatory language, Priestley was not a writer to back away from his opinions in print and he included it, forever branding himself as "Gunpowder Joe". After the publication of this seeming call for revolution in the midst of the French Revolution, pamphleteers stepped up their attacks on Priestley and he and his church were even threatened with legal action.

In 1787, 1789, and 1790, Dissenters again tried to repeal the Test and Corporation Acts. Although initially it looked as if they might succeed, by 1790, with the fears of revolution looming in the minds of many members of Parliament, few were swayed by appeals to equal rights. Political cartoons, one of the most effective and popular media of the time, skewered the Dissenters and Priestley. In the midst of these trying times, it was the betrayal of William Pitt and Edmund Burke that most angered Priestley and his friends; they had expected the two men's support and instead both argued against the repeal. Priestley wrote a series of Letters to William Pitt and Letters to Burke in an attempt to persuade them otherwise, but to no avail; these publications further inflamed the populace against him.

Dissenters such as Priestley who supported the French Revolution came under increasing suspicion as skepticism regarding the revolution grew. In its propaganda against "radicals" such as Priestley, Pitt's administration used the "gunpowder" statement to argue that Priestley and other Dissenters wanted to overthrow the government. Burke, in his famous Reflections on the Revolution in France (1790), tied natural philosophers to the French Revolution and argued that radicals who supported science in Britain "considered man in their experiments no more than they do mice in an air pump". Burke also associates republican principles with alchemy and insubstantial air, mocking the scientific work done by both Priestley and French chemists. He made much in his later writings of the connections between "Gunpowder Joe", science, and Lavoisier—who was improving gunpowder for the French in their war against Britain. Paradoxically, it was Burke, the secular statesman, who argued against science and maintained that religion should be the basis of civil society while Priestley, the Dissenting minister, argued that religion could not provide the basis for civil society and should be restricted to one's private life.

The animus that had been building against Dissenters and supporters of the American and French Revolutions exploded in July 1791. Priestley and several other Dissenters had arranged to have a celebratory dinner on the anniversary of the storming of the Bastille, a provocative action in a country where many disapproved of the French Revolution and feared that it might spread to Britain. Fearing violence, Priestley was convinced by his friends not to attend. Rioters gathered outside the hotel during the banquet and attacked the attendees as they left; they then moved on to the New Meeting and Old Meeting churches—both were burned to the ground. Priestley and his wife fled from their home; although their son William and others stayed behind to protect their property, the mob overcame them and torched Priestley's house, destroying his valuable laboratory and all of the family's belongings. Other homes of Dissenters were burned in the three-day riot. Priestley spent several days hiding with friends until he was able to travel safely to London. The carefully executed attacks of the "mob" and the farcical trials of only a handful of the "leaders" convinced many at the time—and modern historians—that the attacks were planned and condoned by local Birmingham magistrates. When George III was eventually forced to send troops to the area, he said: "I cannot but feel better pleased that Priestley is the sufferer for the doctrines he and his party have instilled, and that the people see them in their true light."

Unable to return to Birmingham, the Priestleys eventually settled in Clapton, near Hackney, where Priestley gave a series of lectures on history and natural philosophy at the new Dissenting academy, New College. Friends helped the couple rebuild their lives, contributing money, books, and laboratory equipment. Priestley tried to obtain restitution from the government for the destruction of his Birmingham property, but he was never fully reimbursed. Priestley also published An Appeal to the Public on the Subject of the Riots in Birmingham (1791) which indicted the people of Birmingham for allowing the riots to occur and for "violating the principles of English government".

Many of the Priestleys' friends urged them to leave Britain and emigrate to either France or the new United States, even though Priestley had received an appointment to preach for the Gravel Pit Meeting congregation. Priestley published many of the sermons he preached there; these sermons, particularly the two Fast Sermons, reflect his growing millenarianism—his belief that the end of the world was fast approaching. After comparing Biblical prophecies to recent history, Priestley concluded that the French Revolution was a harbinger of the Second Coming of Christ. Priestley's works had always had a millennial cast, but after the beginning of the French Revolution, this strain became increasingly prominent. He wrote to a younger friend that while he himself would not see the Second Coming, his friend "may probably live to see it … It cannot, I think be more than twenty years [away]."

Daily life gradually became more difficult for the family: Priestley was burned in effigy along with Thomas Paine; vicious political cartoons continued to be published about him; letters were sent to him from across the country, comparing him to the devil and Guy Fawkes; tradespeople feared the family's business; and Priestley's Royal Academy friends distanced themselves. Their sons were also finding it difficult to keep steady work. As the penalties became harsher for those who spoke out against the government and despite being elected to the French National Convention by three separate departments in 1792, the Priestleys decided to move to America. Five weeks after Priestley left, William Pitt's administration began arresting radicals for seditious libel, resulting in the famous 1794 Treason Trials.

The Priestleys arrived in New York City in 1794; they were immediately feted by various political groups trying to gain Priestley's endorsement. Attempting to steer clear of political discord in his new country, he declined to enter into controversy in what was fast becoming a politically polarized country. As the Priestleys traveled to their new home in Northumberland, Pennsylvania, they stopped in Philadelphia where Priestley gave a series of sermons and helped found the First Unitarian Church of Philadelphia. Priestley turned down an opportunity to teach chemistry at the University of Pennsylvania and the couple began building a home in rural Pennsylvania.

Priestley's attempts to avoid political controversy in the United States failed. In 1795 William Cobbett published Observations on the Emigration of Dr. Joseph Priestley, accusing him of treason against Britain and attempting to undermine his scientific credibility. His political fortunes took an even worse turn when Cobbett obtained a set of letters sent to Priestley by the radical printer John Hurford Stone and the liberal novelist Helen Maria Williams, who were both living in revolutionary France. Cobbett published them in his newspaper, asserting that Priestley and his friends were fomenting a revolution. Priestley was eventually forced to defend himself in print.

Family matters also contributed to making Priestley's time in America difficult. His son Henry died in 1795, probably of malaria. Mary Priestley died soon after in 1796; she was already ill and she never fully recovered after the shock of her son's death. After his wife's death, Priestley wrote to a friend: "I feel quite unhinged and incapable of the exertions I used to make. Having been always very domestic, reading and writing with my wife sitting near me, and often reading to her, I miss her everywhere." Priestley's family relations deteriorated even further in 1800 when a local Pennsylvania newspaper published an article accusing William Priestley, intoxicated with "French principles", of trying to poison the entire Priestley family—both father and son vigorously denied the story.



Priestley continued the educational projects that had always been important to him, helping to establish the "Northumberland Academy" and donating his library to the fledging institution. He and Thomas Jefferson exchanged letters regarding the proper structure of a university and Jefferson relied on this advice when he founded the University of Virginia. Jefferson and Priestley became quite close and when he had completed his General History of the Christian Church, he dedicated it to President Jefferson, writing that "it is now only that I can say I see nothing to fear from the hand of power, the government under which I live being for the first time truly favourable to me."

Priestley tried to continue his scientific investigations in America with the support of the American Philosophical Association, but he rarely received news from Europe; unaware of the latest scientific developments, he was no longer on the forefront of discovery. Although most of his published work focused on defending phlogiston theory, he also did some original work on spontaneous generation and dreams. Despite Priestley's lack of real scientific output at this time, his very presence in America stimulated an interest in chemistry in the young country's inhabitants.

By 1801, Priestley had become so ill that he could no longer write or perform experiments, and on the morning of 6 February 1804, he died. Priestley's epitaph reads: :Return unto thy rest, O my soul, for the :Lord hath dealt bountifully with thee. :I will lay me down in peace and sleep till :I awake in the morning of the resurrection. <div style="clear:both;"></div>

By the time he died in 1804, Priestley had been made a member of every major scientific society in the world and he had discovered numerous substances. The French naturalist George Cuvier, in his eulogy of Priestley, praised his discoveries while at the same time lamenting his refusal to abandon phlogiston theory, calling him "the father of modern chemistry [who] never acknowledged his daughter". Priestley published more than 150 works on topics ranging from political philosophy to education to theology to natural philosophy. He led and inspired British radicals during the 1790s, paved the way for utilitarianism, and helped found Unitarianism. A wide variety of philosophers, scientists, and poets became associationists as a result of his redaction of David Hartley's Observations on Man, including Erasmus Darwin, Coleridge, Wordsworth, J. S. Mill, Alexander Bain, and Herbert Spencer. Immanuel Kant praised Priestley in his Critique of Pure Reason (1781), writing that he "knew how to combine his paradoxical teaching with the interests of religion". Indeed, it was Priestley's aim to "put the most 'advanced' Enlightenment ideas into the service of a rationalized though heterodox Christianity, under the guidance of the basic principles of scientific method".

Yet, considering the extent of Priestley's influence, not a great deal of scholarly work has been done on him. In the early twentieth century, Priestley was most often described as a conservative and dogmatic scientist who was nevertheless a political and religious reformer. In a historiographic review essay, historian of science Simon Schaffer describes the two dominant portraits of Priestley: the first depicts him as "a playful innocent" who stumbled across his discoveries; the second portrays him as innocent as well as "warped" for not better understanding the implications of his discoveries. Assessing Priestley's works as a totality has been difficult for scholars because of his wide-ranging interests. His scientific discoveries have usually been divorced from his theological and metaphysical publications in order to make an analysis of his life and writings easier, but this approach has recently been challenged by scholars such as John McEvoy and Robert Schofield. While early Priestley scholarship claimed that his theological and metaphysical works were "distractions" and "obstacles" to his scientific work, that published in the 1960s, 1970s, and 1980s maintained that Priestley's works constituted a unified theory. But as Schaffer explains, no convincing explanation of what that synthesis might be has yet been set forth. More recently, in 2001, historian of science Dan Eshet has argued that efforts to create a "synoptic view", because they have been "organized around philosophical categories" and have "separate[d] the producers of scientific ideas from any social conflict", only resulted in a rationalization of the contradictions in Priestley's thought.

Priestley has been remembered by the towns in which he served as a reforming educator and minister and by the scientific organizations he influenced. Priestley College in Warrington is named in his honor. In Birstall, Leeds, and Birmingham, he is memorialized through statuary and plaques commemorating him have been posted in Birmingham and Warrington. Also, since 1952 Dickinson College has presented the Priestley Award to a scientist who makes "discoveries which contribute to the welfare of mankind". <div style="clear:both;"></div>

For a complete bibliography of Priestley's works, see the list of works by Joseph Priestley.

*The Rudiments of English Grammar (1761) *A Chart of Biography (1765) *Essay on a Course of Liberal Education for Civil and Active Life (1765) *The History and Present State of Electricity (1767) *Essay on the First Principles of Government (1768) *A New Chart of History (1769) *Institutes of Natural and Revealed Religion (1772–4) *Experiments and Observations on Different Kinds of Air (1774–77) *Disquisitions relating to Matter and Spirit (1777) *The Doctrine of Philosophical Necessity Illustrated (1777) *Letters to a Philosophical Unbeliever (1780) *An History of the Corruptions of Christianity (1782) *Lectures on History and General Policy (1788) *Theological Repository (1770–73; 1784–88)

*Contributions to liberal theory

For a complete bibliography of Priestley's writings, see list of works by Joseph Priestley.

*Lindsay, Jack, ed. Autobiography of Joseph Priestley. Teaneck: Fairleigh Dickinson University Press, 1970. ISBN 0838678310. *Miller, Peter N., ed. Priestley: Political Writings. Cambridge: Cambridge University Press, 1993. ISBN 0521425611. *Passmore, John A., ed. Priestley's Writings on Philosophy, Science and Politics. New York: Collier Books, 1964. *Rutt, John T., ed. Collected Theological and Miscellaneous Works of Joseph Priestley. 2 vols. London: George Smallfield, 1832. *Rutt, John T., ed. Life and Correspondence of Joseph Priestley. 2 vols. London: George Smallfield, 1831. *Schofield, Robert E., ed. A Scientific Autobiography of Joseph Priestley (1733–1804): Selected Scientific Correspondence. Cambridge: MIT Press, 1966.

The most exhaustive biography of Priestley is Robert Schofield's recent two-volume work; several one-volume treatments exist, all somewhat older: Gibbs, Holt and Thorpe. Graham and Smith focus on Priestley's life in America and Uglow and Jackson both discuss Priestley's life in the context of other developments in science. *Gibbs, F. W. Joseph Priestley: Adventurer in Science and Champion of Truth. London: Thomas Nelson and Sons, 1965. *Graham, Jenny. Revolutionary in Exile: The Emigration of Joseph Priestley to America, 1794–1804. Transactions of the American Philosophical Society Vol. 85, 1995. ISBN 0871698528. *Holt, Anne. A Life of Joseph Priestley. London: Oxford University Press, 1931. *Jackson, Joe, A World on Fire: A Heretic, An Aristocrat And The Race to Discover Oxygen. New York: Viking, 2005. ISBN 0670034347. *Schofield, Robert E. The Enlightenment of Joseph Priestley: A Study of his Life and Work from 1733 to 1773. University Park: Pennsylvania State University Press, 1997. ISBN 0271016620. *Schofield, Robert E. The Enlightened Joseph Priestley: A Study of His Life and Work from 1773 to 1804. University Park: Pennsylvania State University Press, 2004. ISBN 0271024593. *Smith, Edgar F. Priestley in America, 1794–1804. Philadelphia: P. Blakiston's Son and Co., 1920. *Tapper, Alan. "Joseph Priestley". Dictionary of Literary Biography 252: British Philosophers 1500–1799. Eds. Philip B. Dematteis and Peter S. Fosl. Detroit: Gale Group, 2002. *Thorpe, T.E. Joseph Priestley. London: J. M. Dent, 1906. *Uglow, Jenny. The Lunar Men: Five Friends Whose Curiosity Changed the World. New York: Farrar, Straus and Giroux, 2002. ISBN 0374194408.

*Anderson, R. G. W. and Christopher Lawrence. Science, Medicine and Dissent: Joseph Priestley (1733–1804). London: Wellcome Trust, 1987. ISBN 0901805289. *Conant, J. B., ed. "The Overthrow of the Phlogiston Theory: The Chemical Revolution of 1775–1789". Harvard Case Histories in Experimental Science. Cambridge: Harvard University Press, 1950. *Crook, R. E. A Bibliography of Joseph Priestley. London: Library Association, 1966. *Crossland, Maurice. "The Image of Science as a Threat: Burke versus Priestley and the 'Philosophic Revolution'". British Journal for the History of Science 20 (1987): 277–307. *Eshet, Dan. "Rereading Priestley". History of Science 39.2 (2001): 127–59. *Fitzpatrick, Martin. "Joseph Priestley and the Cause of Universal Toleration". The Price-Priestley Newsletter 1 (1977): 3–30. *Garrett, Clarke. "Joseph Priestley, the Millennium, and the French Revolution". Journal of the History of Ideas 34.1 (1973): 51–66. *Fruton, Joseph S. Methods and Styles in the Development of Chemistry. Philadelphia: American Philosophical Society, 2002. ISBN 0871692457. *Kramnick, Isaac. "Eighteenth-Century Science and Radical Social Theory: The Case of Joseph Priestley's Scientific Liberalism". Journal of British Studies 25 (1986): 1–30. *Kuhn, Thomas. The Structure of Scientific Revolutions. 3rd ed. Chicago: University of Chicago Press, 1996. ISBN 0226458083. *Haakonssen, Knud, ed. Enlightenment and Religion: Rational Dissent in Eighteenth-Century Britain. Cambridge: Cambridge University Press, 1996. ISBN 0521560608. *McCann, H. Chemistry Transformed: The Paradigmatic Shift from Phlogiston to Oxygen. Norwood: Alex Publishing, 1978. ISBN 089391004X. *McEvoy, John G. "Joseph Priestley, 'Aerial Philosopher': Metaphysics and Methodology in Priestley's Chemical Thought, from 1762 to 1781". Ambix 25 (1978): 1–55, 93–116, 153–75; 26 (1979): 16–30. *McEvoy, John G. "Enlightenment and Dissent in Science: Joseph Priestley and the Limits of Theoretical Reasoning". Enlightenment and Dissent 2 (1983): 47–68. *McEvoy, John G. "Priestley Responds to Lavoisier's Nomenclature: Language, Liberty, and Chemistry in the English Enlightenment". Lavoisier in European Context: Negotiating a New Language for Chemistry. Eds. Bernadette Bensaude-Vincent and Ferdinando Abbri. Canton, MA: Science History Publications, 1995. ISBN 088135189X. *McEvoy, John G. and J.E. McGuire. "God and Nature: Priestley's Way of Rational Dissent". Historical Studies in the Physical Sciences 6 (1975): 325–404. *McLachlan, John. Joseph Priestley Man of Science 1733–1804: An Iconography of a Great Yorkshireman. Braunton and Devon: Merlin Books, 1983. ISBN 0863030521. *McLachlan, John. "Joseph Priestley and the Study of History". Transactions of the Unitarian Historical Society 19 (1987–90): 252–63. *Philip, Mark. "Rational Religion and Political Radicalism". Enlightenment and Dissent 4 (1985): 35–46. *Rose, R. B. "The Priestley Riots of 1791". Past and Present 18 (1960): 68–88. *Schaffer, Simon. "Priestley Questions: An Historiographic Survey". History of Science 22.2 (1984): 151–83. *Sheps, Arthur. "Joseph Priestley's Time Charts: The Use and Teaching of History by Rational Dissent in late Eighteenth-Century England". Lumen 18 (1999): 135–154. *Watts, R. "Joseph Priestley and education". Enlightenment and Dissent 2 (1983): 83–100.

*The Joseph Priestley Society *Joseph Priestley House in PA *Priestley memorial essay (1874) by T.H. Huxley *Priestley artifacts on display at "Revolutionary Players" *www.josephpriestley.com - Comprehensive site which includes a bibliography, links to related sites, images, information on manuscript collections, and other helpful information.

*Priestley biography at the Woodrow Wilson National Fellowship Foundation *Priestley biography at www.historyguide.org *Priestley biography from the Encyclopedia Britannica *Priestley biography at the Chemical Heritage Foundation

"(gb)": From google books *Impregnating Water with Fixed Air (from truetex.com) *A Course of Lectures on Oratory and Criticism (gb) *Lectures on General History, and General Policy (gb) *A General History of the Christian Church (gb) *An History of the Corruptions of Christianity (gb) *Letters to the Right Honourable Edmund Burke Occasioned by his Reflections on the Revolution in France (gb) *The Doctrines of Heathen Philosophy compared with those of Revelation (gb) *Heads of Lectures on Course of Experimental Philosophy (gb) *A Description of a New Chart of History {gb) *Discourses on Various Subjects, Intended to have been delivered in Philadelphia (gb) *Institutes of Natural and Revealed Religion, Vol. 1 of 2 (gb) *Institutes of Natural and Revealed Religion, Vol. 2 of 2 (gb) *An History of Early Opinions Concerning Jesus Christ, Vol. 1 (gb) *An History of Early Opinions Concerning Jesus Christ, Vol. 2 (gb) *An History of Early Opinions Concerning Jesus Christ, Vol. 3 (gb) *An History of Early Opinions Concerning Jesus Christ, Vol. 4 (gb) *A Free Address to Protestant Dissenters (gb) *A Letter to the Rev. Mr. John Palmer, in Defence of Philosophical Necessity (gb) *A Second Letter to the Rev. Mr. John Palmer on Philosophical Necessity (gb) *A Letter to Jacob Bryant, Esq. in Defence of Philosophical Necessity (gb) *Familiar Letters, Addressed to the Inhabitants of Birmingham (gb) *Letters to Dr. Dorne, Dean of Canterbury, to the Young Men who are in a Course of Education for the Christian Ministry at the Universities of Oxford or Cambridge (gb) *Letters to Dr. Horsley: In Answer to His Animadversion on the History of the Corruptions of Christianity (gb) *A Reply to the Animadversions on the History of the Corruptions of Christianity (gb)