Editing Joseph Priestley (section)

==Calne (1773–1780)==
[[File:Portrait of Joseph Priestley by Henry Fuseli.jpg|thumb|left|upright|alt=Portrait of a man sitting on a chair and leaning against a table with books and papers.|A portrait of Priestley commissioned by his publisher and close friend [[Joseph Johnson (publisher)|Joseph Johnson]] from [[Henry Fuseli]] ({{Circa|1783}})<ref>McLachlan, ''Iconography'', 19–20.</ref>]]

In 1773, the Priestleys moved to [[Calne]] in [[Wiltshire]], and a year later [[William Petty, 2nd Earl of Shelburne|Lord Shelburne]] and Priestley took a tour of Europe. According to Priestley's close friend [[Theophilus Lindsey]], Priestley was "much improved by this view of mankind at large".<ref>Qtd. in Gibbs, 91.</ref> Upon their return, Priestley easily fulfilled his duties as librarian and tutor. The workload was intentionally light, allowing him time to pursue his scientific investigations and theological interests. Priestley also became a political adviser to Shelburne, gathering information on parliamentary issues and serving as a liaison between Shelburne and the Dissenting and American interests. When the Priestleys' third son was born on 24 May 1777, they named him Henry at the lord's request.<ref>Schofield (2004), 4–11, 406; Gibbs, 91–94; Jackson, 122, 124, 143–52, 158–62; Thorpe, 80–85; Watts, 96; Holt, 70–94 (includes large quotations from Priestley's letters sent from Europe to Shelburne's sons).</ref>

===Materialist philosopher===
{{further|Joseph Priestley and Dissent}}

Priestley wrote his most important philosophical works during his years with Lord Shelburne. In a series of major [[Metaphysics|metaphysical]] texts published between 1774 and 1780—''An Examination of Dr. Reid's Inquiry into the Human Mind'' (1774), ''Hartley's Theory of the Human Mind on the Principle of the Association of Ideas'' (1775), ''[[Disquisitions relating to Matter and Spirit]]'' (1777), ''[[The Doctrine of Philosophical Necessity Illustrated]]'' (1777), and ''[[Letters to a Philosophical Unbeliever]]'' (1780)—he argues for a philosophy that incorporates four concepts: [[determinism]], [[materialism]], [[causality|causation]], and [[necessitarianism]]. By studying the natural world, he argued, people would learn how to become more compassionate, happy, and prosperous.<ref>McEvoy and McGuire, 326–27; Tapper, 316.</ref>

[[File:PriestleyMatterSpirit.png|thumb|upright|alt=Page reads: "Disquisitions relating to Matter and Spirit. To which is added, The History of the Philosophical Doctrine concerning the Origin of the Soul, and the Nature of Matter; with its Influence on Christianity, especially with Respect to the Doctrine of the Pre-existence of Christ."|By 1782, at least a dozen hostile refutations were published to ''[[Disquisitions relating to Matter and Spirit]]'', and Priestley was branded an [[atheist]].<ref>Schofield (2004), 72.</ref>]] 
Priestley strongly suggested that there is no [[Dualism (philosophy of mind)|mind-body duality]], and put forth a materialist philosophy in these works; that is, one founded on the principle that everything in the universe is made of matter that we can perceive. He also contended that discussing the soul is impossible because it is made of a divine substance, and humanity cannot perceive the divine. Despite his separation of the divine from the mortal, this position shocked and angered many of his readers, who believed that such a duality was necessary for the [[Soul (spirit)|soul]] to exist.<ref>Schofield (2004), 59–76; Gibbs, 99–100; Holt, 112–24; McEvoy and McGuire, 333–34.</ref>

Responding to [[Baron d'Holbach]]'s ''[[The System of Nature|Système de la Nature]]'' (1770) and [[David Hume]]'s ''[[Dialogues Concerning Natural Religion]]'' (1779) as well as the works of the French ''philosophers'', Priestley maintained that materialism and determinism could be reconciled with a belief in God. He criticised those whose faith was shaped by books and fashion, drawing an analogy between the scepticism of educated men and the credulity of the masses.<ref>Tapper, 320; Priestley, ''Autobiography'', 111; Schofield (2004), 37–42; Holt, 93–94, 139–42.</ref>

Maintaining that humans had no [[free will]], Priestley argued that what he called "philosophical necessity" (akin to absolute determinism) is consonant with Christianity, a position based on his understanding of the natural world. Like the rest of nature, man's mind is subject to the laws of causation, Priestley contended, but because a benevolent God created these laws, the world and the people in it will eventually be perfected. Evil is therefore only an imperfect understanding of the world.<ref>Schofield (2004), 77–91; Garrett, 55; Tapper, 319; Sheps, 138; McEvoy (1983), 50; McEvoy and McGuire, 338–40.</ref>

Although Priestley's philosophical work has been characterised as "audacious and original",<ref name=Tap314/><ref>Sheps, 138.</ref> it partakes of older philosophical traditions on the problems of free will, determinism, and materialism.<ref name="MM341">McEvoy and McGuire, 341–45.</ref> For example, the 17th-century philosopher [[Baruch Spinoza]] argued for absolute determinism and absolute materialism.<ref>Leibniz, Gottfried Wilhelm. ''Confessio Philosophi: Papers Concerning the Problem of Evil, 1671–1678''. Trans. Robert C. Sleigh, Jr. New Haven: Yale University Press (2004), xxxviii, 109. {{ISBN|978-0-300-08958-5}}. The [[s:la:Confessio philosophi|original Latin text]] and an [[s:Confessio philosophi|English translation]] of [[Gottfried Wilhelm Leibniz|Leibniz]]'s ''A Philosopher's Creed'' can be found on the Latin and English Wikisources, respectively.</ref> Like Spinoza<ref>
Stewart, Matthew. ''The Courtier and the Heretic: Leibniz, Spinoza, and the Fate of God in the Modern World''. New York: W. W. Norton (2006), 171. {{ISBN|0-393-05898-0}}.</ref> and Priestley,<ref>McEvoy and McGuire, 341.</ref>
[[Gottfried Wilhelm Leibniz|Leibniz]] argued that human will was completely determined by natural laws;<ref name="adams_1998">
Adams, Robert Merrihew. ''Leibniz: Determinist, Theist, Idealist''. New York: Oxford University Press (1998), 10–13, 1–20, 41–44. {{ISBN|0-19-508460-8}}.</ref>
unlike them, Leibniz argued for a "parallel universe" of immaterial objects (such as human souls) so arranged by God that its outcomes agree exactly with those of the material universe.<ref>
Rutherford, 213–18.</ref>
Leibniz<ref>
Rutherford, 46.</ref>
and Priestley<ref>
Schofield (2004), 78–79.</ref>
share an optimism that God has chosen the chain of events benevolently; however, Priestley believed that the events were leading to a glorious millennial conclusion,<ref name=Tap314/> whereas for Leibniz the entire chain of events was optimal in and of itself, as compared with other conceivable chains of events.<ref>
Rutherford, 12–15, 22–45, 49–54.</ref>

===Founder of British Unitarianism===
{{See also|History of Unitarianism}}
When Priestley's friend [[Theophilus Lindsey]] decided to found a new Christian denomination that would not restrict its members' beliefs, Priestley and others hurried to his aid. On 17 April 1774, Lindsey held the first [[Unitarianism|Unitarian]] service in Britain, at the newly formed [[Essex Street Chapel]] in London; he had even designed his own liturgy, of which many were critical. Priestley defended his friend in the pamphlet ''Letter to a Layman, on the Subject of the Rev. Mr. Lindsey's Proposal for a Reformed English Church'' (1774),<ref>Priestley, Joseph. ''Letter to a Layman, on the Subject of the Rev. Mr. Lindsey's Proposal for a Reformed English Church''. London: Printed for J. Wilkie, 1774.</ref> claiming that only the form of worship had been altered, not its substance, and attacking those who followed religion as a fashion. Priestley attended Lindsey's church regularly in the 1770s and occasionally preached there.<ref>Schofield (2004), 26–28; Jackson, 124; Gibbs, 88–89; Holt, 56–64.</ref> He continued to support institutionalised Unitarianism for the rest of his life, writing several ''Defenses'' of Unitarianism and encouraging the foundation of new Unitarian chapels throughout Britain and the United States.<ref>Schofield (2004), 225, 236–38.</ref>

[[File:Priestley Joseph pneumatic trough.jpg|thumb|Equipment used by Priestley in his experiments on gases, 1775|alt=Engraving of assorted scientific equipment, such as a pneumatic trough. A dead mouse rests under one glass canister.]]
[[File:Priestly-2.jpg|alt=Title page to volume I of Experiments and Observations on Different Kinds of Air (1774)|thumb|upright|Title page to volume I of ''Experiments and Observations on Different Kinds of Air'' (1774)]]

===Experiments and Observations on Different Kinds of Air===
{{see also|Wikisource:An Inventory of the Furniture in Dr. Priestley's Study}}

Priestley's years in Calne were the only ones in his life dominated by scientific investigations; they were also the most scientifically fruitful. His experiments were almost entirely confined to "airs", and out of this work emerged his most important scientific texts: the six volumes of ''[[Experiments and Observations on Different Kinds of Air]]'' (1774–86).<ref>Priestley, Joseph. ''[[Experiments and Observations on Different Kinds of Air]]''. 3 vols. London W. Bowyer and J. Nichols, 1774–77. There are several different editions of these volumes, each important.</ref><ref>See Gibbs 67–83 for a description of all of Priestley's experiments during this time; Thorpe, 170ff.</ref> These experiments helped repudiate the last vestiges of the [[Classical element|theory of four elements]], which Priestley attempted to replace with his own variation of [[phlogiston theory]]. According to that 18th-century theory, the combustion or [[redox|oxidation]] of a substance corresponded to the release of a material substance, ''phlogiston''.<ref>Thorpe, 167–68; Schofield (2004), 98–101.</ref>

Priestley's work on "airs" is not easily classified. As historian of science [[Simon Schaffer]] writes, it "has been seen as a branch of physics, or chemistry, or natural philosophy, or some highly idiosyncratic version of Priestley's own invention".<ref>Schaffer, 152.</ref> Furthermore, the volumes were both a scientific and a political enterprise for Priestley, in which he argues that science could destroy "undue and usurped authority" and that government has "reason to tremble even at an air pump or an electrical machine".<ref>Qtd. in Kramnick, 11–12; see also Schofield (2004), 121–24.</ref>

Volume I of ''Experiments and Observations on Different Kinds of Air'' outlined several discoveries: "nitrous air" ([[nitric oxide]], NO); "vapor of spirit of salt", later called "acid air" or "marine acid air" ([[anhydrous hydrochloric acid]], HCl); "alkaline air" ([[ammonia]], NH<sub>3</sub>); "diminished" or "dephlogisticated nitrous air" ([[nitrous oxide]], N<sub>2</sub>O); and, most famously, "dephlogisticated air" ([[oxygen]], O<sub>2</sub>) as well as experimental findings that showed plants revitalised enclosed volumes of air, a discovery that would eventually lead to the discovery of [[photosynthesis]] by [[Jan Ingenhousz]]. Priestley also developed a "nitrous air test" to determine the "goodness of air". Using a [[pneumatic trough]], he would mix nitrous air with a test sample, over water or mercury, and measure the decrease in volume—the principle of [[eudiometer|eudiometry]].<ref name="Fruton">Fruton, 20, 29</ref> After a small history of the study of airs, he explained his own experiments in an open and sincere style. As an early biographer writes, "whatever he knows or thinks he tells: doubts, perplexities, blunders are set down with the most refreshing candour."<ref>Schofield (2004), 98; Thorpe, 171.</ref> Priestley also described his cheap and easy-to-assemble experimental apparatus; his colleagues therefore believed that they could easily reproduce his experiments.<ref>Schofield (1997), 259–69; Jackson, 110–14; Thorpe, 76–77, 178–79; Uglow, 229–39.</ref> Faced with inconsistent experimental results, Priestley employed phlogiston theory. This led him to conclude that there were only three types of "air": "fixed", "alkaline", and "acid". Priestley dismissed the [[History of chemistry#17th and 18th centuries: Early chemistry|burgeoning chemistry]] of his day. Instead, he focused on gases and "changes in their sensible properties", as had natural philosophers before him. He isolated [[carbon monoxide]] (CO), but apparently did not realise that it was a separate "air".<ref>Schofield (2004), 93–105; Uglow, 240–41; see Gibbs 105–16 for a description of these experiments.</ref>

====Discovery of oxygen====
{{see also|Wikisource:The Mouse's Petition}}

[[File:Bowood House laboratory.jpg|thumb|left|The laboratory at Lord Shelburne's estate, [[Bowood House]] in Wiltshire, in which Priestley discovered oxygen|alt=Photograph of a laboratory, with glass-encased, wooden bookcases on two walls and a window on the third. There is a display case in the middle of the room.]]

In August 1774 he isolated an "air" that appeared to be completely new, but he did not have an opportunity to pursue the matter because he was about to tour Europe with Shelburne. While in Paris, Priestley replicated the experiment for others, including French chemist [[Antoine Lavoisier]]. After returning to Britain in January 1775, he continued his experiments and discovered "vitriolic acid air" ([[sulphur dioxide]], SO<sub>2</sub>).{{citation needed|date=February 2024}}

In March he wrote to several people regarding the new "air" that he had discovered in August. One of these letters was read aloud to the Royal Society, and a paper outlining the discovery, titled "An Account of further Discoveries in Air", was published in the Society's journal ''[[Philosophical Transactions]]''.<ref>Priestley, Joseph. "[https://www.jstor.org/pss/106209 An Account of Further Discoveries in Air]". ''[[Philosophical Transactions]]'' 65 (1775): 384–94.</ref> Priestley called the new substance "dephlogisticated air", which he made in the famous experiment by [[burning glass|focusing the sun's rays]] on a sample of [[mercuric oxide]]. He first tested it on mice, who surprised him by surviving quite a while entrapped with the air, and then on himself, writing that it was "five or six times better than common air for the purpose of respiration, inflammation, and, I believe, every other use of common atmospherical air".<ref>Qtd. in Schofield (2004), 107.</ref> He had discovered [[oxygen]] gas (O<sub>2</sub>).{{citation needed|date=February 2024}}

[[File:Shelburne.jpg|thumb|upright|[[William Petty, 2nd Earl of Shelburne|William Petty-Fitzmaurice, 1st Marquess of Landsdowne]] – who sympathised with  [[Unitarianism]]<ref>{{cite book |last1=Wagner |first1=P. |title=Hypoxia |date=2012 |publisher=Springer |page=10 |isbn=978-1-4419-8997-0 |url=https://books.google.com/books?id=XSDjBwAAQBAJ&dq=unitarian+William+Petty,+2nd+Earl+of+Shelburne&pg=PA11 |access-date=2 January 2024}}</ref> – built a laboratory for the famous dissenter at [[Bowood House]].|alt=Half-length portrait of a man wearing furred robes and a white wig and looking regal. Underneath his white robes, he is wearing red and gold and he is sitting in a red chair.]]

[[File:OxygenApparatus.jpg|thumb|alt=Reproduction of Joseph Priestley's oxygen apparatus|Reproduction of Joseph Priestley's oxygen apparatus]]

Priestley assembled his oxygen paper and several others into a second volume of ''Experiments and Observations on Air'', published in 1776. He did not emphasise his discovery of "dephlogisticated air" (leaving it to Part III of the volume) but instead argued in the preface how important such discoveries were to rational religion. His paper narrated the discovery chronologically, relating the long delays between experiments and his initial puzzlements; thus, it is difficult to determine when exactly Priestley "discovered" oxygen.<ref>Schofield (2004), 105–19; see also Jackson, 126–27, 163–64, 166–74; Gibbs, 118–23; Uglow, 229–31, 241; Holt, 93.</ref> Such dating is significant as both Lavoisier and Swedish pharmacist [[Carl Wilhelm Scheele]] have strong claims to the discovery of oxygen as well, Scheele having been the first to isolate the gas (although he published after Priestley) and Lavoisier having been the first to describe it as purified "air itself entire without alteration" (that is, the first to explain oxygen without phlogiston theory).<ref>Kuhn, 53–55.</ref>

In his paper "Observations on Respiration and the Use of the Blood", Priestley was the first to suggest a connection between blood and air, although he did so using [[phlogiston theory]]. In typical Priestley fashion, he prefaced the paper with a history of the study of respiration. A year later, clearly influenced by Priestley, Lavoisier was also discussing respiration at the [[French Academy of Sciences|Académie des sciences]]. Lavoisier's work began the long train of discovery that produced papers on oxygen respiration and culminated in the overthrow of phlogiston theory and the establishment of modern chemistry.<ref>Schofield (2004), 129–30; Gibbs, 124–25.</ref>

Around 1779 Priestley and Shelburne – soon to be the [[Marquess of Lansdowne|1st Marquess of Landsdowne]] – had a rupture, the precise reasons for which remain unclear. Shelburne blamed Priestley's health, while Priestley claimed Shelburne had no further use for him. Some contemporaries speculated that Priestley's outspokenness had hurt Shelburne's political career. Schofield argues that the most likely reason was Shelburne's recent marriage to Louisa Fitzpatrick—apparently, she did not like the Priestleys. Although Priestley considered moving to America, he eventually accepted [[Birmingham]] New Meeting's offer to be their minister.<ref>Schofield (2004), 141–43; see also Jackson, 198–99; Holt, 81–82.</ref>

Both Priestley and Shelburne's families upheld their Unitarian faith for generations. In December 2013, it was reported that [[Sir Christopher Bullock]]—a direct descendant of Shelburne's brother, [[Thomas Fitzmaurice (MP)]]—had married his wife, [[Lupton family|Lady Bullock]], née Barbara May Lupton, at London's Unitarian [[Essex Street Chapel|Essex Church]] in 1917. Barbara Lupton was the second cousin of [[Family of Catherine, Duchess of Cambridge|Olive Middleton]], née Lupton, the great-grandmother of [[Catherine, Duchess of Cambridge]]. In 1914, Olive and Noel Middleton had married at Leeds' [[Mill Hill Chapel]], which Priestley, as its minister, had once guided towards Unitarianism.<ref>{{cite news |last1=Nikkah |first1=Roya |title=The Duchess discovers blue blood in her own family |url=https://www.telegraph.co.uk/news/uknews/kate-middleton/9747412/Duchess-of-Cambridge-discovers-blue-blood-in-her-own-family.html |website=UK Sunday Telegraph |date=16 December 2012 |page=9 |access-date=8 July 2014 |url-status=live |archive-url=https://web.archive.org/web/20141029061649/http://www.telegraph.co.uk/news/uknews/kate-middleton/9747412/Duchess-of-Cambridge-discovers-blue-blood-in-her-own-family.html |archive-date=29 October 2014}}</ref>