Features appear in each issue of Pennsylvania Heritage showcasing a variety of subjects from various periods and geographic locations in Pennsylvania.

When Joseph Priestley (1733-1804) is remembered today, it’s usually for his 1774 discovery, in England, of oxygen. Few know he was a noted theologian, political progressive, and prolific author whose scientific contributions include the development of the carbonation process, the identification of carbon monoxide, and early experiments in electricity. He counted Benjamin Franklin, Thomas Jefferson, and James Watt among his friends. Yet, Priestley was also a controversial figure whose views were so odious to some of his countrymen that his house, Fair Hill in Birmingham, was burned in a riot, and he and his family left England. Priestley spent the last ten years of his life in Northumberland, Pennsylvania, where he continued his work in science, religion, and education. But even in this democratic republic, his liberal ideas were frequently received with intolerance, and the peace that he so ardently desired was often elusive.

To appreciate Priestley’s life and work as a dissenting minister and educator, and to more clearly understand his wide-ranging curiosity about natural philosophy and politics, it’s helpful to examine the social and intellectual climate of late eighteenth-century England. Andrea Bashore, acting historic site administrator of the Joseph Priestley House in Northumberland County, administered by the Pennsylvania Historical and Museum Commission (PHMC), believes that it is difficult for people today to understand the mindset of Priestley’s era. “I see it as a challenge,” she explains. “For me, it’s important to study the times in which a person lived as a way of bringing accuracy and excitement to historical interpretation.”

On one hand, there was the Enlightenment, a heady movement of rationality, liberality, science, and humanitarianism that emerged from the seventeenth century Age of Reason. A scientific approach was applied to political and social issues, giving rise to a sense of human progress and belief in the state as its rational instrument. On the other hand, this conflicted with the reality that enlightened ideas were tolerated by governmental and religious leaders only if they posed no threat to the status quo. Church and state formed an unnatural and powerful alliance. King Henry VIII (1491-1547) had broken with Rome and rejected the authority of the Pope, establishing the Church of England with himself as supreme head. His daughter Elizabeth I (1533-1603) reasserted this authority; by edict, she required uniformity in religion. All subjects had to subscribe to the Thirty-Nine Articles defining Anglican doctrines. Clergy functioned as civil officers, with bishops sitting in the House of Lords.

Of course, the religious philosophy of the established church was not universally shared. There were Dissenters or Nonconformists, among them Congregationalists, Presbyterians, Independents, Catholics, Baptists, Quakers, and Unitarians. Members were not permitted to attend state schools and were excluded from military and civil appointments. Religious groups – except Catholics, Jews, and Unitarians – attained limited freedom when the 1689 Act of Toleration permitted them to have their own places of worship and to appoint and dismiss their own preachers. However, their clergy had to take an oath of loyalty to the crown and subscribe to most of the Thirty-Nine Articles.

Into this combustible atmosphere, Joseph Priestley was born on March 13, 1733, in Fieldhead near Leeds, Yorkshire, the son of a clothmaker. His mother died when he was six; two years later his father remarried, and the young Priestley was placed in the care of his father’s childless older sister Sarah Keighley and her husband John. Sarah Keighley was a pious woman of Dissenting Calvinistic principles, and, while under her care, Joseph Priestley followed her beliefs. However, he became seriously ill about 1750 and experienced a crisis of faith: believing that a religious experience “produced by the immediate agency of the Spirit of God” was a requirement for salvation, and frantic that he had not had such an experience, Priestley began to question the doctrine of experienced salvation.

Priestley’s aunt was tolerant of other people’s beliefs, and encouraged her nephew’s liberal education in academic subjects and religion. In her home, he freely met and studied with Dissenting ministers. He was relieved to talk with “heretics” who, like himself, questioned original sin. Despite a stammer that would make delivering sermons challenging, Priestley chose to make the ministry his profession. At the age of nineteen, he entered the Nonconformist academy at Daventry to begin those ministerial studies. Here he began the religious journey that led him eventually to Unitarianism, the form of Christianity that sees God as one being, and denies the doctrine of the Trinity (that God exists as Father, Son, and Holy Spirit). A serious, well-prepared student, Priestley was allowed to skip many first-year courses. By all accounts he spent his time well at Daventry, and reveled in the debate and discussions he found with instructors and students.

In 1755, Priestley completed his schooling at the Academy, and accepted a pulpit in Needham Market in Suffolk, where his liberal religious views, especially his anti-Trinitarian beliefs, caused friction with parishioners and other ministers. After three years, he transferred to a church in Nantwich, Cheshire, where he found satisfaction. The congregation accepted Priestley’s theology and appreciated his work. His school was successful: he taught both boys and girls and continued development of his educational theories and methods. Science was included in the curriculum.

For Priestley, science and religion were completely compatible. He looked at his work in “natural philosophy,” as science was termed, as an attempt to gain a better understanding of God and the universe. His scientific explorations continued at Warrington Academy, one of the leading Dissenting institutions, where he took a position as language tutor in 1761.

The following year the twenty-nine-year-old Priestley married twenty-year-old Mary Wilkinson, the sister of one of his Nantwich students and daughter of ironmonger John Wilkinson. Mary would be an intellectual companion, a careful housewife, and a faithful supporter during their thirty-four-year marriage. The couple, who eventually had three sons and a daughter, took in students as boarders to supplement their income.

It was during this period that Priestley became interested in history and its documentation. He developed and published his Chart of Biography, and received an honorary Doctor of Laws degree from the University of Edinburgh. He saw the need for a written record of experimental science, and, encouraged by Benjamin Franklin, began with electricity. Priestley had been elected a fellow of the Royal Society of London in 1766 and met many important scientists, including Franklin, who became a mentor. Franklin helped Priestley obtain background material for his 1767 book, The History and Present State of Electricity with Original Experiments. Their friendship continued until Franklin’s death in 1790.

By 1767, Priestley needed more income, so he took employment as minister to the congregation at Mill Hill Chapel in Leeds, where he began to experiment with gases, known then as “airs.” Priestley invented the process of carbonation, for which he received the Royal Society’s prestigious Copley Medal in 1773, the same year he became literary companion and librarian to William Petty, second Earl of Shelburne. During their association, Priestley was able to travel with Shelburne, to continue studying gases, and to write about education, religion, and science.

On August 1, 1774, Priestley made the discovery for which he is most famous: isolating “dephlogisticated air,” that is to say, the element oxygen. It had been thought that combustion was accompanied by the release of a substance known as phlogiston, rather than the gain of oxygen as scientists now know. In Priestley’s “dephlogisticated air,” a candle burned vigorously and sustained a mouse longer than in “common air.” After breathing the gas, Priestley wrote, “I fancied that my breast felt peculiarly light and easy for some time afterwards.”

French aristocrat and scientist Antoine Lavoisier (1743-1794) was also working with gases, and several historians imply that he appropriated Priestley’s work to make his “own” discovery of oxygen. The two met once, and they discussed “dephlogisticated air.” However, Lavoisier approached his work quantitatively, concluding that combustion involved a combination with a substance from air, rather than the loss of phlogiston.

While in Shelburne’s employ, Priestley made significant achievements in science. He published four volumes of Experiments and Observations on Different Kinds of Air, and gathered material for a fifth. Shelburne encouraged these pursuits, giving Priestley forty pounds yearly for expenses associated with experiments. Priestley’s scientific discoveries seemed boundless; along with oxygen, he later identified ten other compounds, including ammonia. He figured out part of photosynthesis. He discovered blood’s function in respiration. He continued to experiment with electricity and optics.

He was elected to numerous learned societies, among them The Royal Society, London; the French Academy of Sciences; the Imperial Academy of Sciences, St. Petersburg; the Philosophical Society, Orleans; The Society at Haarlem, Netherlands; the Lisbon Royal Academy of Sciences, Portugal; the American Philosophical Society, Philadelphia; and the American Academy of Arts and Sciences, Boston.

In time, Priestley’s religious and political views became embarrassing to Lord Shelburne, and they separated in 1780. Priestley moved to Birmingham, an industrial city with a population of one hundred thousand, to serve as co-minister of the New Meeting Church, where he grew increasingly controversial. Three theological assertions particularly enraged leaders of the Church of England: his denial of the Trinity, a disavowal that was legally punishable by imprisonment and fine; his premise that there was no such thing as an immortal soul that existed as a separate substance; and his belief that conversion required discipline and study. Politically, he was also seen as a threat since he advocated Parliamentary reform and had supported both the American Revolution and the French Revolution.

Priestley was caricatured and denounced. Abhorred by defenders of the religious establishment and feared as an agent of reform by government officials whose fortunes were tied to the continuation of the current system, Priestley became a target in a mounting national hysteria. The English tradition (some might say myth) of formal religious freedom precluded direct attack on his religious beliefs, so his political inclinations bore the brunt. On July 14, 1791, the second anniversary of the fall of the Bastille, the Birmingham Riot erupted. A mob began burning the residences and meeting houses of suspected anti-royalists. Priestley received news that he was at risk, but – ever the rationalist – he was reluctant to accept the fact that something so illogical could happen.

He finally agreed to leave his home, and he and his family barely escaped before the mob torched their house and its contents. Ostensibly, the rioters were hunting “seditious” members of the Constitutional Society who met for dinner to celebrate the anniversary of the French Revolution. Although a founding member of the Constitutional Society, Priestley, did not attend the event; nevertheless, he was the primary target of the “Church and King” revolutionaries who destroyed his home, pursued him and his wife to the nearby home of a friend, then to the home of their daughter and son-in-law, until the couple ultimately fled to London. The rioters, many of whom were inebriated, terrorized the community for four days until government troops reestablished relative calm. The toll: eleven homes and two chapels in Birmingham were destroyed.

Four years later, in An Appeal to the Public, on the Subject of the Riots in Birmingham, a disappointed Priestley criticized the hypocritical system that had not attempted to quell the riot, a system that, in fact, actually fomented it. “I was born an Englishman … and supposed I had the protection of .. constitution and laws for my inheritance. But I have found myself greatly deceived.”

After fleeing Birmingham, Priestley served at the Unitarian Dissenter Chapel in Hackney, near London, and taught science and history in the nearby Dissenter New College. With the help of friends, he began to rebuild his library and laboratory. However, the situation remained tense and uncomfortable – Priestley could not even find succor in the company of his fellow scientists in the Royal Society, as they shunned him – so on April 8, 1794, Joseph and Mary Priestley set sail for America.

Eight weeks later the couple arrived to a warm welcome, first in New York, where leading citizens, merchants, college officials, representatives of various societies, even the governor, received them. Next they moved on to the capital, Philadelphia. Philadelphia possessed many advantages, but the Priestleys considered it unhealthy; the previous year, more than four thousand people had died of yellow fever (see “Plagued! Philadelphia’s Yellow Fever Epidemic of 1793” by William C. Kashatus III, Spring 1993). Their sons Joseph, William, and Henry had joined with fellow Englishmen to purchase land north of Northumberland, Pennsylvania, in the hopes of establishing a Dissenter Colony. Their colony never materialized, but the elder Priestleys moved to Northumberland, a village of a hundred houses along the Susquehanna River. They lived temporarily in a small house with their son Joseph and his family.

The Priestleys began designing a new house, a self-contained estate intended to be stylish and grand. Construction began, but two tragedies struck before the house was completed. In December 1795, Joseph and Mary’s youngest son, Henry (nicknamed “Harry”) died, and Mary succumbed to tuberculosis the following September. When the house, a fine example of Federal-style architecture, was finished in 1798, Priestley moved in with his son Joseph, his wife Elizabeth, and their children.

In England, Priestley had been reviled for ideas that might have seemed too American: democracy, support for representational government, religious freedom, freedom of thought. Yet in America, he was persecuted for his religious beliefs and his politics, which some found suspiciously English. When a letter to Priestley from John Stone in Paris, hinting of a revolution in England, found its way into the hands of William Cobbett, an unnaturalized English immigrant editing a Philadelphia newspaper, Cobbett published it and declared that Priestley was an “apostle of sedition.” Cobbett eventually fled to England after the eminent Philadelphia physician Benjamin Rush brought a libel suit against him – winning five thousand dollars – but the damage was irreparable.

Undeclared war existed between the United States and France, then under the rule of the “reign of terror.” A nervous Federalist majority in Congress passed the 1798 Alien and Sedition Acts. The Alien Energy Act authorized the president to deport any alien without a hearing, while the Sedition Act made even minor criticisms of the government indictable as high misdemeanors. Priestley had not been naturalized, and Timothy Pickering, Secretary of State under President John Adams, recommended deportation under the act, most likely to make him an example. The ostensible reason was that Priestley’s friend, Thomas Cooper, who was also living in Northumberland, had published essays critical of the Federalist administration. Although Priestley had not seen the essays until after they were printed, Pickering tried to convince Adams that Priestley had helped create them. Fortunately, Adams did not approve of the act, nor was he swayed by Pickering’s arguments. Indeed, despite some philosophical differences, Priestley and Adams had been friends since 1787 when Adams had served as ambassador to England.

In Priestley’s ten years in Pennsylvania, he identified carbon monoxide as a distinct “air,” published more than thirty scientific papers, and wrote more than a dozen religious works, including his six-volume History of the Christian Church. He traveled to Philadelphia to present lectures on religion; his 1796 lectures on “Evidences of Revelation” led to the formation of the First Unitarian Church in Philadelphia. His library and laboratory were probably the best in the country at the time.

Priestley died on February 6, 1804, and was buried in the Northumberland cemetery, next to his wife and son. After his death the house changed hands several times, and was acquired by the Commonwealth of Pennsylvania in 1961. In 1968, the Pennsylvania Historical and Museum Commission began refurbishing the property to reflect the period of Priestley’s residence. Recent renovations include completion this year of the carriage barn and other outbuildings and fencing as built by Priestley. The site has been designated a National Historic Chemical Landmark by the American Chemical Society, which formed after an 1874 meeting at the Priestley House to celebrate the hundredth anniversary of the discovery of oxygen. It is also a National Historic Landmark, and is entered on the National Register of Historic Places.

A guided tour of the Joseph Priestley House offers a look at restored Federal architecture, and helps visitors understand the complex and intriguing individual. Furnishings and reproductions of the period are featured. Among the original Priestley household objects on display are a French marble clock that he received as a gift from the Marquis de Lafayette for his support of the French Revolution, a chess set he and Mary used often, and many leather-bound books.

In his laboratory, located on the north side of the house, Priestley continued his scientific experiments and discovered carbon monoxide in 1799, and here, in the most important historical part of the house, one feels the Priestley presence most keenly. Glassware, scientific apparatus, and evidence of a fume hood evoke scenes of him vigorously applying himself to his studies in “natural philosophy.”

“Priestley’s laboratory has become a shrine for many visitors to this historic site,” says Andrea Bashore. “Many chemists, scientists, teachers, and students travel to Northumberland with the laboratory as their primary focus.” A proposal for restoring the laboratory has been formulated, based on extensive research completed in 1996. The lengthy restoration process is in the initial stages and will continue over several years. “When completed,” comments Bashore, “the restored laboratory will offer visitors a unique educational opportunity to experience the daily research workspace of the noted gentleman-scientist, Joseph Priestley.”

The house and exhibits bring visitors closer to understanding and appreciating the enigmatic Joseph Priestley. One cannot fail to admire his depth and breadth of knowledge, his varied fields of inquiry, and his fearlessness in speaking his beliefs even when those views would put him in peril. Perhaps President Thomas Jefferson said it best. After his March 1801 inauguration, the “scientist president” wrote to his kindred spirit, “Science and honesty are replaced on their high ground; and you, my Dear Sir, as their great apostle, are on the pinnacle.”

The Joseph Priestley House is open Tuesday through Saturday, 9 A.M. to 5 P.M.; Sunday, noon to 5 P.M. The historic site is closed Mondays and holidays, except for Memorial Day, Independence Day, and Labor Day. There is an admission charge. Persons with disabilities who need special assistance or accommodation should telephone or write the historic site in advance of their visit to discuss their needs. Persons who are deaf, hard of hearing, or speech impaired who wish to contact a hearing person via Text Telephone may use the PA Relay Center at 800-654-5984. For more information, write: Joseph Priestley House, 472 Priestley Avenue, Northumberland, PA 17857; or telephone (570) 473-9474.

Northumberland County was created in 1772 – just two decades before the arrival of Joseph Priestley – in response to expanding settlement along the upper reaches of the Susquehanna River following the French and Indian War. The earliest governmental record of the existence of Shamokin, present-day Sunbury, dates to 1728 when traders were authorized to establish trade with the Native Americans. Sunbury, the county seat, was laid out in 1772, and is the home of the Northumberland County Historical Society. Founded in 1925, the historical society collects documents, and interprets the county’s history, in addition to administering the nearby site of Fort Augusta for the PHMC. Built in 1756, Fort Augusta was occupied by Pennsylvania militia and became one of the largest and most important of the many frontier forts in the Commonwealth. North of Sunbury, in Turbotville, the historic Warrior Run Church, erected in 1835, is administered for the PHMC by the Fort Freeland Heritage Society, which sponsors a number of family programs and activities.

Information about historic attractions in Northumberland County and northcentral Pennsylvania is available by writing: Susquehanna Valley Visitors Bureau, 219D Hafer Rd., Lewisburg, PA 17837; or by telephoning (570) 524-7234 or toll-free (800) 525-7320. Individuals may also visit the Susquehanna Valley Visitors Bureau website.


For Further Reading

Clark, John Ruskin. Joseph Priestley: Comet in the System. Northumberland, PA: The Friends of the Joseph Priestley House, Inc., 1994.

Graham, Jenny. Revolutionary in Exile: The Emigration of Joseph Priestley to America, 1794-1804. Philadelphia: The American Philosophical Society, 1995.

Kieft, Lester. Joseph Priestley and the Priestley House. Lewisburg, PA: Bucknell University, 1983.

Lukehart, Peter M., ed. Joseph Priestley in America, 1794-1804. Carlisle, PA: Dickinson College, 1994.

Schofield, Robert E. The Enlightenment of Joseph Priestley: A Study of His Life and Work from 1733-1773. University Park: The Pennsylvania State University Press, 1997.


For her invaluable assistance and enthusiasm, as well as her thorough review of the text, the author and editor thank Andrea Bashore, acting historic site administrator of the Joseph Priestley House.


Sharon Hernes Silverman of West Chester, Chester County, writes frequently for Pennsylvania Heritage. Her most recent feature, “New Sweden and the New World: History Lessons from the Morton Homestead,” appeared in the Winter 1999 edition.