Marker Text
The noted English scientist, discoverer of oxygen, and Unitarian theologian lived in Northumberland, 1794 to 1804. His home and laboratory along the river are now a Priestley memorial and museum.

Behind the Marker


Two portraits of Joseph Priestly speak volumes about the differences of his...
Credit: Courtesy of the Chemical Heritage Foundation Image Archives. Chemists" Club Collection
Although he is known to most people as the discoverer of oxygen, Joseph Priestley was, with Benjamin Franklin, perhaps the most universal Anglo-American genius produced by the eighteenth-century Enlightenment. Priestley was born near Leeds in England on March 13, 1733. Raised in a strict Calvinist family, he studied to become a minister, and learned Greek, Latin, Hebrew, French, German, and Italian. He discovered, however, that his strong liberal beliefs conflicted with his church's teachings. In particular, Priestley denied the divinity of Christ, and sought to purify a church he believed wallowed in age-old impurities.

As he wrote in his 1786 tract, "The Importance and Extent of Free Enquiry in the Matters of Religion," he urged his readers to be "laying gunpowder . . . under the old building of error and superstition, which a single spark may hereafter inflame."


In 1801, when he was sixty eight, Priestly sat for a portrait by Rembrandt Peale....
Credit: Courtesy of the American Philosophical Society Library


Throughout his life, Priestley considered himself a minister and a theologian, serving several congregations in England-- most of which dismissed him for his radical ideas. He wrote numerous multi-volume works expounding his Unitarian ideology that God was one rather than three beings, and a benevolent deity who was facilitating progress and bringing good out of evil.

While serving as provincial agent for Pennsylvania and several other provinces in the 1760s, Benjamin Franklin helped foster Priestley's interest in science. In his first scientific work, "The History and Present State of Electricity, with Original Experiments," (1766) Priestley put forth his first major discovery: that graphite conducts electricity. Elected that year to the prestigious Royal Society, he continued his experiments. Noticing that the gas generated from his brewery extinguished lighted wood chips and that it drifted to the ground around the vat, which indicated that it was heavier than normal air, Priestley then devised a method to produce the gas - later identified as carbon dioxide - at his home laboratory. When the "heavy gas," as he called it, was dissolved in water, he found that it had a very pleasant taste. His invention of this "soda water" earned him election to the French Academy of Sciences in 1772 and a medal from the Royal Society in 1773. Continuing his experiments, the controversial Unitarian minister became the first scientist to identify oxygen and nitrous oxide, and the first to document the process of photosynthesis.


Already infamous for his radical politics and religious heresies, Joseph Priestley...
Credit: Library of Congress, Prints and Photographs Division


Priestley may have been a brilliant and highly acclaimed scientist, but his non-conformist religious and political views caused considerable controversy. During the American Revolution, he was protected by Lord Shelburne, who, after becoming prime minister in 1782, negotiated peace with the new United States. Shelburne granted him a life pension of £150, appointed him tutor to his sons, and took him to France, where he exchanged ideas with renowned French scientist Antoine Lavoisier. But in 1785, a British court officially outlawed his History of Corruptions of Christianity (1782), a book in which he attempted to expose the hypocrisy of the Church of England. His public support of the French Revolution - he was one of the founders of the Constitution Society, founded on Bastille Day, 1791, which sought to abolish the British monarchy - and radicalism resulted in the torching of his Birmingham home and church by an angry mob in 1791.


Joseph Priestley spent the final ten years of his life in Pennsylvania, splitting...
Credit: Pennsylvania Historical and Museum Commission
Priestley relocated to London to escape the crowd, but the persecution continued. In 1794, he immigrated with his family to Pennsylvania to escape possible imprisonment, exile, or death.

In Philadelphia, Priestley was enthusiastically welcomed by the scientific and civic organizations of the early republic. His political ideas, however, proved as controversial in his new home as in England. Siding with the Jeffersonian Republicans, he became a prime example of the Federalists' contention that Irish and British immigrants who supported the radical French Revolution had been instrumental in persuading native-born citizens of various economic classes to form the "Democratic societies" that opposed the Federalist Party and its support of Great Britain. Instead of representing "the people," the Federalists claimed that the Democratic societies were created by "detestable banditti of foreign invaders."



Long a haven to people fleeing religious and political persecution in Europe,...
Credit: PHMC Historic Sites & Museums
Priestley wrote for the Philadelphia Aurora, the Republican newspaper edited by Benjamin Franklin at first secretly then publicly, supported the Jeffersonian cause in the Susquehanna River town of Northumberland where he had made his home. Here, with his three sons, he hoped to found a college and center of learning, but the frontier settlers were open neither to his cultural nor religious ideas. They were more sympathetic to his politics, however, unlike Secretary of State Timothy Pickering who urged President John Adams to deport Priestley under the provisions of the Alien Enemies Act of 1798, which permitted the chief executive to arbitrarily expel "undesirable" aliens.

With the defeat of the Federalists in the election of 1800, harassment of Priestley ceased as Thomas Jefferson, who agreed with his politics and was interested in his experiments, assumed the presidency. Priestley continued his experiments and added to his voluminous writings on religious, political, and scientific matters. He died quietly in his Northumberland home on February 6, 1804.