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Joseph Priestley

This entry is part 3 of 3 in the series Age of Reason and Enlightenment

Joseph Priestley radical dissenter and champion for the open and inquiring mind.

Joseph Priestly was quite possibly one of the most important thinkers of the Enlightenment. His direct and open inquiry into both religious beliefs and ideas was also directed at science, politics and society.

Who was Joseph Priestley?

He was born on the 13th March 1733 in a village called Birstall near Leeds in Yorkshire. His father, Jonas Priestley was a cloth finisher and in such an occupation there was little money coming into the Priestley household he was the eldest of six children all very close in age and so Joseph was sent from about the age of one, to live with his grandfather. His mother died when Joseph was about six and he was sent to live with a childless aunt and uncle Sarah and John Keighley. They quickly realised that Joseph was a gifted learner and his Aunt Sarah, did all she could to nurture this bright and gifted young soul.

Joseph Priestley and Calvanism.

Aunt Sarah was a dissenter, a Presbyterian but she was also open to new ideas and teachings and kept an open house to all dissenting ministers, even if she found some of their views difficult to assimilate she gave them voice if and only if she thought them to be good and honest men. Joseph Priestley therefore felt the full force of the Calvanist foundations of the Presbyterian household he grew up in. He struggled with the belief that a new birth by agency of the Spirit of God was necessary for his own salvation. In 1749 at the age of sixteen, Joseph became seriously ill and close to death. The conversion experience for his salvation, so drilled into him by his Calvanist beliefs was to cause him great distress as he stood facing death. Since Priestley had experienced no such rebirth, where did that leave him? Early in his life this made him question and develop what he saw as rational principles of religion and would form part of the approach he developed in all his areas of study. The most immediate effect was that Joseph proposed Universal Salvation, after all he did not see himself as less honest or true than the men who attended meetings at his aunts house. Already he was showing signs of the individual thinker he would become as an adult and his local Presbyterian church refused to allow him to become a full member.

The emergence of the brilliant mind of Joseph Priestley.

Once Aunt Sarah saw the scholar in Joseph she sent him to attend the local Grammar school where he learned Greek, Latin, and Hebrew in preparation for his training to become a Presbyterian minister however his illness left him with a stutter that took away any thoughts that he could deliver the sermons that would be demanded of him. Aunt Sarah employed a private tutor for Joseph, Reverend George Haggerstone. The Reverend Haggerstone flooded Joseph Priestley’s young life with new learning. Joseph was a brilliant linguist and learnt a host of European languages as well as Syrian, Chaldean, a Neo-Aramaic dialect of the Semitic language family and a rare language. This opened up a wealth of new works including the mathematics of the Arabic countries and of course the Greeks. It was Haggerstone who taught him higher maths and natural sciences and awakened in him the desire to know more.

Daventry Academy.

At the age of nineteen, Joseph entered Daventry Academy, this highly regarded academy was a liberal dissenting academy. Joseph Priestley loved and treasured his time at the academy and later in his life he wrote an open letter to William Pitt extolling the purpose and benefit of such places of learning and as such was way ahead of his time and gives thought for how we view our higher education establishments even now. Priestley wrote;

While your universities resemble pools of stagnant water, ours, (the dissenting academies) are like rivers, which, taking their natural course, fertilize a whole country.

Joseph Priestley to William Pitt 1787

So Priestley entered Daventry Dissenting Academy in Northampton in 1752 to study theology but here he turned his back on Calvinism, his view on Universal Salvation was just the starting point of his new religious calling. He rejected Calvinism and became a Rational Dissenter. Rational Dissenters rejected a church based on tradition and authority and believed in a benevolent God. This as surely as anything tells much about the character of Joseph Priestley. His Aunt Sarah found his opinions too much to bear and despite her obvious love for Joseph, she rejected him. It was at Daventry that Joseph Priestly encountered David Hartley’s ‘Observations On Man’. In this work Priestly found deep satisfaction, for it re-enforced his own no nonsense approach to religion and to life. Hartley insisted that education was the source of all life’s perfections. That it is only through education that mankind grows and progresses. It was as if Hartley, with his earnest morality and faith was a mirror to Joseph Priestly’s own being.

After graduating.

After graduating, Priestley worked as a Unitarian Minister at Needham in Suffolk. He was only twenty two years old but his strident beliefs proved to be too much for his new congregation. He turned his vision elsewhere and his passion for education led him to Nantwich in Cheshire where he founded a school. He introduced pupils to scientific instruments including an electrical machine and an air-pump.

Onto the Warrington Academy.

He was offered a teaching post at Warrington Academy in Lancaster in 1761 to teach modern languages but Joseph Priestly did so much more at the academy.

Warrington Academy

He taught himself law so that he could engage with some of England’s top lawyers. He learnt history and immersed himself ever more deeply into politics. He used science, religion, history and politics to argue over a range of subjects. He liked facts but was never afraid to theorise as long as he could argue the point with others. His fear was dogmatism that stifled progress.

The following year Priestley was both ordained and married. His wife was Mary Wilkinson, daughter of the industrialist Isaac Wilkinson and brother of the iron master, John. Mary gave birth to their first child, a daughter, named Sarah after Priestley’s Aunt Sarah, in 1763.

‘The History and Present State of Electricity’.

Joseph Priestly was fascinated by electricity and he experimented as much as he was able. In 1767 he wrote ‘The History and Present State of Electricity’ in this he stated he observed that the electrical ‘force’ is subject to the same laws as gravity (the square of the distances). So whenever he was able Priestly sought out the company of other scientists including Benjamin Franklin. He shared his scientific philosophy of being able to question and theorise openly without fear of ridicule or of losing ones reputation. Dogmatism was unacceptable to Priestly.

Priestly’s approach to science theory spilled over into religion.

For Priestly there had to be free religious inquiry. Christ as an idol was unacceptable. Priestly adopted Socinianism in which Christ is seen as a ‘man’ the same as the rest of us but chosen by God to do his work on Earth. He wrote about his beliefs in the ‘Theological Repository’, hoping to draw out discussion of religion in a free thinking way. The world however was not ready for Joseph Priestly and he made little headway either inside or outside the Christian community.

He moved to Mill Hill in 1767, receiving a stipend of 100 guineas and a house. He lived in the minster’s house north of the chapel before moving to be with Lord Shelburne and preaching his last sermon at Mill Hill in May, 1773.

In 1774 he joined with Theophilus Lindsey in founding the first place of worship with the name ‘Unitarian’ at Essex Street in London. At this time radicals Thomas Paine and Thomas Jefferson both visited this new Church. The headquarters of the modern Unitarian denomination still stand in the premises Priestley and Lindsey bought.

During his time in Leeds his research led to the discovery of oxygen in 1774 and he also co founded the Leeds Library and the Infirmary.

What did John Wesley have to say about Joseph Priestley?

‘one of the most dangerous enemies of Christianity’

Joseph Priestly took the quite savage attack by Wesley very well, after all didn’t he champion open debate and discussion? But he must have been so frustrated by the dogma of Wesley. He saw it as a way to further improve himself, a way to learn.

The science continued alongside his religious journey.

He studied optics and wrote a history on the subject in 1772 but it was chemistry that caught his eye and through his work he had caught the eye of other notable scientists including Joseph Banks who, in 1771, wanted him to join Cook on his second Pacific expedition as ‘scientific observer’. Banks was not put off by Joseph’s outspoken approach to religion but others held a different view and he did not travel on the expedition.

‘Experiments and observations on Different Kinds of Air’.

Priestley’s work on ‘dephlogisticated’ air, that was eventually called Oxygen, is surely what we all now remember Joseph Priestley for.
In a series of experiments culminating in 1774, Priestley found that air is not an elementary substance, but a composition, a mixture, of gases. Among this mixture was the colourless and highly reactive gas he called ‘dephlogisticated air’. Priestley never gave it the name Oxygen, it was the French chemist Antoine Lavoisier who gave it that title.

How did Priestley come to investigate the composition of air?

 Instead of going on the Cook voyage in 1773, the Earl of Shelburne asked Priestley to work in his library at Bowood House in Calne Wiltshire. This role of librarian and intellectual player for the earl and his family gave Priestley access to many in the scientific, social and political circles that wouldn’t have necessarily open to a man such as Priestley. It also gave him a quiet place to carry out his experiments.

These experiments were wide ranging as Priestley began a series of observations that would prove to be immensely important. By placing animals and plants in vessels containing various isolated gases he observed a mouse dying in a jar and that same jar caused a flame to go out however when he placed a green plant into the same vessel and exposing it to sunlight, the air was refreshed. He was the first person to make the link between animals and plants and carbon dioxide and oxygen, what we now know as photosynthesis.

On August 1, 1774, he conducted his most famous experiment when he isolated oxygen from mercuric oxide. He observed the gas kept a mouse alive four times longer than ordinary air and he observed how much more intensely a flame burned when placed in it.

Priestley called his discovery ‘dephlogisticated air’. He based his name on the theory that it supported combustion so well because it had no phlogiston in it. Priestley was not the only scientist looking at the composition of air but he was the first to recognise the significance of what he observed and publish. He made the following observation.


‘was not sensibly different from that of common air, but I fancied that my breast felt peculiarly light and easy for some time afterwards. Who can tell but that in time, this pure air may become a fashionable article in luxury. Hitherto only two mice and myself have had the privilege of breathing it.’


Priestley and the Lunar Society.

In 1780 Joseph Priestley took up residence in Birmingham, here the industrial machine was gripping the populace like nowhere else in the country and Priestley enjoyed the company of the new industrialists. He joined Matthew Boulton and others at The Lunar Society. Here he learnt to voice his radical ideas and opinions which grew stronger. He criticized the Poor Laws and energized by the French revolutionaries, turned away from believing in a monarchy led country to believing that Parliament should hold the power.

In 1791 a dinner was held in Birmingham to commemorate the storming of The Bastille. The authorities who had been watching Priestley become ever more radical stirred up a mob who burnt the dissenting chapels and then turned on his house destroying his laboratory and library.

Joseph Priestley
Joseph Priestley’s House destroyed by the mob 1791

Joseph Priestley leaves for America.

It seemed there could be no future for Joseph Priestley in England. The French had honoured him with a seat in the National Assembly which only infuriated the doubters and politicians even further and so Priestley and his family set sail for America and ended up in Northumberland Pennsylvania. His Unitarianism was not welcome there either but he continued to call for social, political and religious reform. He died on 6th February 1804, leaving behind him much unfinished business.

Joseph Priestley Headstone

The legacy of Joseph Priestley.

Joseph Priestley was a polymath, a spirited man who formed strong opinions and saw that all aspects of humankind were connected, that the spiritual, political and social forces that shaped society, also shaped how people learnt and progressed.

Would he be disappointed to know that the thing he is most well known for is the discovery of Oxygen?

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