Priestley, Joseph

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Joseph Priestley

Born March 24, 1733

Fieldhead, England

Died February 6, 1804

Northumberland, Pennsylvania

Scientist, philosopher, teacher, minister

"Truth can never have a fair chance of being discovered, or propagated, without the most perfect freedom of inquiry and debate."

J oseph Priestley is credited for being one of the founding fathers of the science known as chemistry. In addition to discovering oxygen, he conducted experiments with fixed air (carbon dioxide), which eventually led to the development of carbonated beverages, or soda pop. His good friend Benjamin Franklin (1706–1790) aroused his interest in electricity, and it was Priestley who discovered that graphite is a useful electrical conductor. In addition to his scientific interests, Priestley was a published philosopher whose beliefs differed from the religious majority of the day. As a result, he and his family were outcasts, subjected to ridicule and physical violence. Priestley brought to America a new religion—Unitarianism—although the movement would not be referred to as such for years to come.

A curious mind leads to internal conflict

Joseph Priestley was born the oldest of six siblings to Jonas (a weaver) and Mary (a farmer's daughter) near Leeds, England, on March 13, 1733. When the Gregorian calendar (the one used today) came into use in 1751, Priestley changed his birth date to March 24. Because the six children were born close together, Mary sent her eldest child to live with her parents while he was young. He returned to the Priestley home upon his mother's death, only to be adopted by his father's sister at the age of nine. During his stay with his aunt, Priestley was introduced to philosophical and religious discussions as well as liberal (open to new ideas) political attitudes. He lived with his aunt Sarah until her death in 1764.

Although Priestly attended local schools throughout his childhood, he was stricken with tuberculosis, an infectious disease of the lungs, while still a teenager and was forced to drop out. His illness did not prevent him from learning, however. He used the time to teach himself French, German, Italian, and several other languages. In addition, he also learned the basics of geometry, algebra, and mathematics.

After recovering from his bout with tuberculosis, the young Priestley was determined to begin training for the career goal he had always envisioned, that of the ministry. After living in a household in which lively discussion of religion and politics was an everyday occurrence, however, he found himself questioning some of the basic beliefs of the Calvinist faith, a religion that embraces a particularly stern and rigid moral code. In particular, Priestley did not believe in the trinity—the Father, Son, and Holy Ghost. Rather than attend the strict religious academy near his home, he chose to attend the more liberal Daventry Academy. There he had the chance to learn not just traditional subjects, but those involving natural and experimental philosophy as well. While at the academy, his inclination for and interest in experimentation was nurtured.

Interest in science, priority in theology

Although he clearly possessed scientific interests and abilities, Priestley remained intent on becoming a minister. Upon graduation from Daventry, he accepted a position with a poverty-stricken congregation in Suffolk. However, he was not successful, largely due to his Unitarian tendencies. The Unitarian faith rejects the concept of the trinity, and though it upholds the moral teachings of Jesus, it denies his status as divine, believing instead that God exists as only one being. Priestley eagerly accepted an invitation to preach in Cheshire, where churchgoers were more apt to accept his theology. In addition to preaching, Priestley became schoolmaster and private tutor, a promotion that brought with it an increase in salary. He used the extra income to fund his private research.

He grew in popularity at Cheshire and eventually accepted a position as tutor at a Dissenting Academy in Warrington. Dissenting Academies were the center of liberal education in this era as traditional universities did not welcome dissenters, or people whose beliefs were not in keeping with the conformist beliefs and theories of the time. Priestley spent six years at Warrington. In 1762, he married Mary Wilkinson, daughter of English inventor John Wilkinson (1728–1808).

Career takes a turn

While still at Warrington, Priestley applied for an ordination to the Dissenting ministry a month before his wedding was to take place. His application was accepted, and he began giving lectures on history and general policy in the hopes of opening previously unexplored academic roads to his students. He became a popular public speaker.

Priestly enjoyed an annual month-long trip to London, during which time he met with other distinguished dissenters. While on one of these visits, he became friends with Benjamin Franklin. Their friendship encouraged Priestley's natural interests in experimentation, and he soon discovered the use of graphite as an electrical conductor. Through the American statesman, Priestley was introduced to the scientific community at large, and his first scientific paper, The History and Present State of Electricity, was published. The paper included results from his original experiments. As a result of his publication, he was elected as a Fellow of the Royal Society in 1766. When it became clear that the paper was too difficult for the ordinary reader to understand, Priestley set out to publish another edition, this time with illustrations. When he was unable to find anyone to make the drawings, he did them himself. During the course of his work, he accidentally discovered the use of India rubber as an eraser of pencil markings. Thus, the crude version of the modern pencil eraser was born.

Not long after his debut into the publishing world, Priestley became the minister at Mill Hill. He moved his family to Mill Chapel in Leeds in 1767. His most important discoveries began that year, as his focus changed from that of electricity to air. Priestley had convenient access to fixed air (carbon dioxide), as his house was situated near a brewery. Through repeated experimentation, the scientist eventually discovered that bubbles, or effervescence, found in sparkling beverages and natural spas were really the result of nothing more than water that contained fixed air. The paper he wrote and published on this subject won him the impressive Copley Medal of the Royal Society.

Discovers oxygen

Although Priestley is credited with discovering oxygen, it is more correct to say that he isolated dephlogisticated air, the term once used for oxygen. In 1774, Priestley was working with another scientist, Carl Scheele (1742–1786). Scheele figured out that heating liquids results in the release of gas, and using this information, Priestley isolated oxygen by heating mercuric oxide. Upon making his discovery, he is quoted as saying, "I have discovered an air five or six times as good as common air." One hundred years after the scientist's greatest contribution to chemistry, he was honored for his discovery at a meeting that led to the founding of the American Chemical Society.

Priestley left Leeds to accept a position as librarian and tutor for William Petty (1737–1805), Earl of Shelburne. He received a generous salary, and it was during this time that he published the works for which he is most famous: DisquisitionsRelating to Matter and Spirit and Experiments and Observations. After enjoying a productive period as a chemist from 1773 to 1780, Priestley quit his job with Lord Shelburne on good terms and left to resume a life in the ministry.

Immigrates to America amid controversy

By this time, Priestley's family had grown to include three sons and a daughter. He moved them to Birmingham, England, in 1780 and joined the Lunar Society, a group of about a dozen men with similar interests. Commonly referred to as "Lunatics," these men were interested in natural science and literature as well as all things metaphysical (involving the supernatural, among other things). They met once a month on the Monday nearest the full moon. This particular time was chosen so that the members could travel home by moonlight, able to see but not necessarily seen by others who might not agree with what the Lunatics had been doing.

During these years in Birmingham, Priestley wrote a number of philosophical and religious works. The publication of these writings caused great controversy. Their author, whose beliefs got him labeled a dissenter, was attacked in magazines and pamphlets as well as in churches. He was considered an agent of the Devil.

In eighteenth–century England, dissenters were deprived the rights of citizenship and those considered Unitarian could not legally be tolerated. With the commencement of the French Revolution (1789–99), dissenters sided with those citizens who were being oppressed by the government. In July 1791, a dinner was to be held to celebrate Bastille Day, a celebration of independence in France, similar to the Fourth of July in America. Priestley disappointed the crowds raging outside the hotel where the dinner was held by not attending. Later in the evening, the rioters regrouped, and, under the influence of alcohol, burned down the New Meetinghouse where Priestley preached. They also burned down the Old Meetinghouse. Someone ran ahead and warned Priestley of the approaching mob, and Priestley and his wife left their home with only the clothes they were wearing. They stopped at a neighbor's home, only to realize the rioters were already at their home, looking for them. As they moved on, they looked back in time to see their home ablaze. Priestley lost all his earthly possessions, including his unpublished papers and his science lab.

The Priestleys escaped to London but found little peace. Priestley continued to be attacked from church pulpits and in pamphlets, and now he was receiving letters threatening his life. An honorary citizen of France as a result of his support during the Revolution, he was denounced, or criticized, by the Royal Society and forced to resign his membership. It was clear that neither he nor his family were welcome in London, so they immigrated to America, leaving London on April 7, 1794. Priestley had just turned sixty-one.

America welcomes the persecuted

Once in America, Priestley took his family to Philadelphia, Pennsylvania, where he joined one of his sons and a mutual friend, Thomas Cooper, in hopes of establishing a colony for English Dissenters. The colony never became reality, and the family moved to Northumberland, a small town on the banks of the Susquehanna River. Tragedy struck within the year, however, when both Priestley's wife and youngest son died. Although Priestley kept himself busy with experiments and preaching, he was no longer the cheerful man he once was.

Lonely for intellectual discussion and company, Priestley spent the long winter months in Philadelphia. He founded the first Unitarian Church there, and his sermons were highly regarded by some of the most prestigious thinkers of the day, including future presidents John Adams (1735–1826; served 1797–1801) and Thomas Jefferson (1743–1826; served 1801–9). Jefferson admired Priestley and consulted with him on important matters, such as the content of the curriculum of the University of Virginia, which he was planning to establish. Clearly, Priestley had found a home where his differing views were considered cause for celebration rather than condemnation.

In 1801, the aging Priestley fell ill, and he never fully recovered his health. On February 5, 1804, he had his children brought to his bedside, where he encouraged them to continue in their love for one another. He died quietly the following day at the age of seventy-one and was buried next to his beloved wife and son.

—Rebecca Valentine

For More Information


Hirsch, Alison Duncan, and Kyle R. Weaver. Joseph Priestley House: Pennsylvania Trail of History Guide. Mechanicsburg, PA: Stackpole Books, 2003.

Horvitz, Leslie Alan. Eureka! Scientific Breakthroughs That Changed the World. Hoboken, NJ: Wiley, 2001.

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.

Web Sites

Silverman, Sharon Hernes. "Joseph Priestley, Catalyst of the Enlightenment." Originally printed in Pennsylvania Heritage Magazine. Available on Pennsylvania Historical and Museum Commission Web site. (accessed on March 23, 2004).

Stelter, Eric, and Susana Suarez. "Joseph Priestley." The History of Chemistry: 1992 Woodrow Wilson Summer Institute. (accessed on March 23, 2004).

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Priestley, Joseph

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