JOSEPH PRIESTLEY
(b. March 13, 1733, Birstall Fieldhead, near Leeds, Yorkshire, Eng.--d.
Feb. 6, 1804, Northumberland, Pa., U.S.), English clergyman, political
theorist, and physical scientist whose work contributed to advances in
liberal political and religious thought and in experimental science. He
is best remembered as one of the discoverers of the element oxygen. (see
also Index: Unitarianism)
Education and early career
Priestley was the oldest of six children
of a modestly successful cloth dresser. For several years during his childhood
Joseph was often sickly, but, perhaps as compensation, he became an avid
learner on his own. Although his parents were Calvinists, they were open
to other religious views and wanted him to enter the ministry of the Dissenting
church, the diverse congregations of which, such as Presbyterian or Independent,
did not conform to the Church of England. To prepare himself, he studied
"Hebrew, Chaldee, Syriac, and a little Arabic" with a local Dissenting
minister.
With improving health, in 1752 he entered a new Dissenting Academy at
Daventry, Northamptonshire, one of the educational institutions that, in
the 18th century, was established independently by Nonconformists.
These academies offered high-quality education and attracted the best teachers
and students. His unorthodox opinions developed even more as he added to
the required curriculum his own intensive study of history, philosophy,
and science, and a daily translation of 10 folio pages of Greek. In 1755
he left Daventry Academy to become assistant minister to the independent
Presbyterian congregation in Needham Market, Suffolk, but, as he had become
a "furious freethinker," his unorthodox and even heretical opinions gradually
lost him the confidence of his orthodox congregation. "After much pain
and thought," he renounced the doctrine of the Atonement; moreover, his
examination of St. Paul's epistles in the New Testament satisfied him that
the Apostle's reasoning "was in many places far from being conclusive."
Priestley's
intellectual development passed from the Calvinism of his family, through
Arianism, with its denial of Christ's divinity, to a rational Unitarianism,
with its complete denial of the Trinity. At no stage of this development,
however, did he ever waver in the sincerity of his religious convictions
or in the genuine piety of his life.
In 1758 Priestley transferred to a more sympathetic congregation
in Nantwich, Cheshire, where he opened a day school with 36 students. Becoming
interested in science at this time, he provided them with "philosophical
instruments," such as an air pump and a static generator for electrical
demonstrations. His teaching success led to his appointment in 1761 as
a tutor in language and literature at Warrington Academy in Lancashire.
Because the universities and learned professions were closed to Dissenters,
Priestley
developed new courses that were suitable for students preparing for
careers in industry and commerce. Textbooks were not available, and these
he set himself to write. In 1761 he published the Rudiments
of English Grammar, a work that was radical in its reliance on description
of actual English usage as opposed to prescription on the basis of dead
classical languages; it remained in use for 50 years. Ordained a Dissenting
minister in 1762 at Warrington, in the same year he married Mary Wilkinson,
aged 18, the only daughter of an ironmaster at Bersham in Wales. They had
a daughter and three sons. (see also Index: education,
history of )
Priestley enriched the curriculum with his Theory of Language
and Universal Grammar (1762), Chart of Biography (1765), Essay
on a Course of Liberal Education for Civil and Active Life (1765),
and Lectures on History and General Policy (1765, 1788). By emphasizing
history, science, and the arts rather than the classics of university curricula,
he sought to prepare students for a practical life. His educational activities
made Warrington Academy the most distinguished school of its kind in England.
The degree of LL.D. was conferred on him by Edinburgh University in 1765.
Work in science
Priestley became even more interested in science while attending
lectures and demonstrations on practical chemistry given in 1763-65 by
the surgeon Matthew Turner. Beginning in 1765, Priestley spent a
month of every year in London, where he met the leading men of science,
including the American statesman and inventor Benjamin
Franklin. On the basis of his electrical experiments, Priestley in
1766 was elected to membership in the Royal Society of London. The next
year, with Franklin's encouragement and generous loan of the requisite
books, he published The History and Present
State of Electricity, an original work in which he summarized the knowledge
of electricity
to his time and described his own experiments. He anticipated the inverse
square law of electrical attraction with his observation that when he electrified
a hollow sphere there was no charge inside. He also discovered that charcoal
conducts electricity and noted the relationship between electricity and
chemical change, whereby one could cause the other. This work "drew him
into a large field of original experiments" that were not in electricity.
As he became more interested in chemistry, he reflected on the similarity
between the processes of burning and respiration.
In 1767 Priestley was appointed minister of Mill Hill Chapel,
in Leeds, Yorkshire, where he had more leisure for writing and experimenting.
Although not primarily theoretical in his approach to science, he was able
to perceive what research would be most fruitful. He studied gases,
or "airs,"
as they were then called, a subject that led him to perform many significant
experiments. The facts he discovered became central in the theoretical
development of chemistry. His work on gases began while he was living next
to a brewery in Leeds, where he observed "fixed-air" (carbon dioxide) as
it effervesced from vats of fermenting liquor. Before his work, only three
gases were known: air, carbon dioxide, and hydrogen. With zeal and enthusiasm
he discovered 10 new "airs," four in 1767-73 while at Leeds: nitric oxide
(nitrous air), nitrogen dioxide (red nitrous vapour), nitrous oxide (diminished
nitrous air, later called "laughing gas"), and hydrogen chloride (marine
acid air). His success resulted in large part from his ability to design
ingenious laboratory apparatus, particularly an improved pneumatic trough,
and his skill in its manipulation. Moreover, by collecting gases above
mercury in the trough, instead of in water, he was able to isolate, by
trial and error, those that were water-soluble. His description of the
gas experiments in the Philosophical
Transactions, "On Different Kinds of Air" (1772), promptly drew the
attention of the French chemist Antoine-Laurent
Lavoisier, who provided a theoretical interpretation.
Concurrently with these experiments, Priestley developed rapidly
as a political theorist. Representative of 18th-century liberal thought
was his Essay on the First Principles of Government,
and on the Nature of Political, Civil, and Religious Liberty (1769),
in which he emphasized individualism; he believed that people should have
a voice in their government and power over their own actions. The English
economist Jeremy
Bentham acknowledged that this influential book inspired his phrase "the
greatest happiness of the greatest number." Throughout his life Priestley
was
an ardent believer in human progress and perfectibility.
In 1772 Priestley's History and Present
State of Discoveries Relating to Vision, Light, and Colours was an
original contribution to optics. It brought an invitation to join Capt. James
Cook's second voyage of exploration (1773-75) as an astronomer, but he
was obliged to decline when opposition mounted to his Unitarian views.
His technique for "impregnating water with fixed-air" (using sulfur acid
and chalk), however, was suggested for use on the voyage to make drinking
water palatable--and also later made possible the soda-water industry.
In December 1772, William Fitzmaurice-Petty, 2nd earl of Shelburne,
later 1st marquis of Lansdowne, appointed Priestley as librarian,
literary companion, and tutor to his two young sons, on generous terms,
with the freedom to preach and write as he wished. He settled at the Shelburne
estate at Calne, Wiltshire, in July 1773. The following November he was
awarded the Copley Medal by the Royal Society for his experiments on gases,
on which he continued to report in a series of volumes entitled Experiments
and Observations on Different Kinds of Air, 6 vol. (1774-86).
Discovery of oxygen
Priestley's most famous discovery occurred on Aug. 1, 1774, when
he obtained a colourless gas by heating red mercuric oxide (he called it
mercurius
calcinatus per se). Finding that a candle would burn in it "with a
remarkably vigorous flame," he called it "dephlogisticated air" because
he believed, accepting prevailing theory, that ordinary air became saturated
with phlogiston
when it could no longer support combustion
or life. (Phlogiston was thought to be a material that was transferred
during burning and respiration; a unifying idea in 18th-century chemistry,
it avoided quantitative considerations but was the reverse of the oxidative
interpretation of combustion and respiration established by Lavoisier in
1789.) Priestley was not yet sure, however, that he had discovered
a "new species of air." (Oxygen
was also discovered by the Swedish chemist and apothecary Carl
Wilhelm Scheele, probably by 1773.) The following October Priestley
accompanied
Shelburne on a journey through Belgium, Holland, Germany, and France, where
in Paris he informed Lavoisier how he obtained his new "air." The meeting
of the two scientists was highly significant for the future of chemistry:
Lavoisier required no more than the barest intimation of the success of
Priestley's experiments to appreciate their significance. He immediately
repeated them and in 1775-80 conducted intensive investigations from which
he correctly deduced the elementary nature of oxygen, recognized it as
the active "principle" of the atmosphere, interpreted its role in combustion
and respiration, and gave it its name (1789). Priestley, however,
did not accept all of Lavoisier's views and continued in particular to
uphold the phlogiston theory until, in his old age, he was its last champion.
Other significant scientific discoveries.
Continuing his studies of the atmosphere, Priestley discovered ammonia
(alkaline air), sulfur dioxide (vitriolic acid air), silicon tetrafluoride
(fluor acid air), nitrogen (also discovered by Daniel Rutherford in 1772),
and a gas later identified as carbon monoxide. Of striking significance
was his observation that light was important for plant growth and that
green plants gave off "dephlogisticated air" (really oxygen). These observations
became fundamental to the systematic work on photosynthesis
by the Dutch physician Jan Ingenhousz (begun in 1779) and by the Swiss
clergyman-naturalist Jean Senebier during the next two decades. Drawing
then on his earlier knowledge of electricity, Priestley decomposed
ammonia by sparking with electric sparks and noticed the formation of dew
when mixtures of hydrogen and oxygen are exploded.
In 1779, for reasons not entirely clear, Priestley left Shelburne's
employ and settled in the industrial town of Birmingham as minister of
the New Meeting congregation. He received a small annuity from Shelburne,
and friends raised a subscription to defray the expenses of his experiments.
The years at Birmingham were the happiest and busiest of his life. He wrote
books on religion and theology and published sermons, tracts, and catechisms.
In his History of the Corruptions of Christianity
(1782),
he rejected most of the fundamental doctrines of Christianity, including
the Trinity, predestination, and the divine verbal inspiration of the Bible
and traced them to their historical sources of error. This work aroused
another storm of protest. By the time of the French Revolution he had acquired
a reputation as the antagonist of all establishments, both political and
religious.
Priestley regularly took part in meetings of Birmingham's Lunar
Society, which met monthly at the full moon. Flourishing independently
of the Royal Society of London, this organization in 1766-91 actively promoted
science and its applications to industry and crafts. There, Priestley
was
the honoured colleague of the naturalist Erasmus Darwin, the pottery manufacturer
Josiah Wedgwood, and the inventor of the steam engine, James Watt. Concluding
his scientific work, he observed that "calces" (oxides) are changed to
the metallic state (reduced) when heated in hydrogen, but he did not notice
that water is also produced, and he gave a phlogistic interpretation.
During these years, Priestley was widely known as the defender
of the principles of the French
Revolution and an ardent advocate of civil and religious liberty. He angered
the antirevolutionary populace by publicly disagreeing with the Reflections
on the Revolution in France (1790), written by the British statesman Edmund
Burke, who opposed the Revolution. On July 14, 1791, on the second anniversary
of the fall of the Bastille prison in Paris, an outbreak of mob violence
occurred in Birmingham, in the course of which Priestley's house,
library, and laboratory were destroyed. He was driven from Birmingham,
never to return.
For the next two years Priestley resided at Hackney, near London,
where he taught at the New College (Hackney College); but the progress
of the French Revolution, the execution of Louis XVI in 1793, and the declaration
of war against France the same year excited further rancour against him.
His three sons had emigrated to the United States in August 1793; Priestley
and
his wife followed in April 1794, taking up residence in Northumberland,
Pa. He was welcomed by various learned societies, including the American
Philosophical Society, and offered the chair of chemistry at the University
of Pennsylvania, but he refused to accept any public office.
During his years in America, Priestley continued his literary
and religious activities, but he was hampered in his scientific work by
the difficulties of communicating with his friends in England. He published
in the United States the last four volumes of his six-volume A General
History of the Christian Church (vol. 1-2, 1790-1803, and vol. 3-6,
1802-03). He was a friend and correspondent of two leaders of the American
Revolution, John Adams and Thomas Jefferson, both of whom held views on
religion similar to his own. The Doctrines
of Heathen Philosophy Compared with Those of Revelation appeared after
his death. It had been written at the suggestion of Jefferson, who felt,
however, that "it did not do justice to the undertaking," adding that Priestley
"felt
himself pressed by the hand of death." He died at Northumberland in 1804.
(S.R.)
BIBLIOGRAPHY.
The best book-length biography, which does justice to all aspects of Priestley's
work, is F.W. Gibbs, Joseph Priestley (1965). A popular description
of Priestley's discoveries in chemistry is in Kenneth Davis, The
Cautionary Scientists: Priestley, Lavoisier, and the Founding of
Modern Chemistry (1966).
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