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Cartwright, J. The discovery of oxygen: Student guide. Department of Chemistry, University of Chester. Conant, J. Harvard case histories in experimental science Vol. Cambridge: Harvard University Press. Kipnis, N. CrossRef Google Scholar. A history of science approach to the nature of science: Learning science by rediscovering it. McComas Ed. Dordrecht: Kluwer. Misgeld, W. The historical-genetical approach to science teaching at the Oberstufen-Kolleg. Priestley, J. His scientific discoveries have usually been divorced from his theological and metaphysical publications to make an analysis of his life and writings easier, but this approach has been challenged recently by scholars such as John McEvoy and Robert Schofield.

Although early Priestley scholarship claimed that his theological and metaphysical works were "distractions" and "obstacles" to his scientific work, scholarship published in the s, s, and s maintained that Priestley's works constituted a unified theory. However, as Schaffer explains, no convincing synthesis of his work has yet been expounded. Priestley has been remembered by the towns in which he served as a reforming educator and minister and by the scientific organisations he influenced.

Two educational institutions have been named in his honour— Priestley College in Warrington and Joseph Priestley College in Leeds [] now part of Leeds City College —and an asteroid, Priestley , discovered in by Duncan Waldron. Additional recognition for Priestley's work is marked by a National Historic Chemical Landmark designation for his discovery of oxygen, made on 1 August , at the Priestley House in Northumberland, Penn. May we not infer from this experiment, that the attraction of electricity is subject to the same laws with that of gravitation, and is therefore according to the squares of the distances; since it is easily demonstrated, that were the earth in the form of a shell, a body in the inside of it would not be attracted to one side more than another?

The most exhaustive biography of Priestley is Robert Schofield's recent two-volume work; several one-volume treatments exist, all somewhat older: Gibbs, Holt and Thorpe. Graham and Smith focus on Priestley's life in America and Uglow and Jackson both discuss Priestley's life in the context of other developments in science.

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From Wikipedia, the free encyclopedia. English theologian, chemist, educator, and political theorist. Priestley by Ellen Sharples [1]. Northumberland, Pennsylvania , US. Further information: Joseph Priestley and education. Further information: Joseph Priestley and Dissent. See also: History of Unitarianism. Priestley's Study. See also: Wikisource:The Mouse's Petition.


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See also: Chemical Revolution. Main article: Priestley Riots. See also: Joseph Priestley House. Main article: List of works by Joseph Priestley. The Royal Society. Archived from the original on 1 August Retrieved 1 August Schlesinger General Chemistry 4th ed. The difficulty in precisely defining the time and place of the "discovery" of oxygen, within the context of the developing chemical revolution , is one of Thomas Kuhn 's central illustrations of the gradual nature of paradigm shifts in The Structure of Scientific Revolutions.

Oxford Dictionary of National Biography online ed. Oxford University Press. Subscription or UK public library membership required. The Rudiments of English Grammar ; adapted to the use of schools. With observations on style. London: Printed for R. Griffiths, Retrieved 26 June Philadelphia, Penns. Archived from the original on 2 June Retrieved 11 September London: Printed for C.

Henderson under the Royal Exchange; T. Becket and De Hondt in the Strand; and by J. Johnson and Davenport, in Pater-Noster-Row, A Chart of Biography. London: J. Johnson, St. London: Engraved and published for J. London: Printed for J. Johnson, The History and Present State of Electricity , with original experiments. Dodsley, J. Johnson and T. Cadell, See: J. A Familiar Introduction to the Study of Electricity. Dodsley; T. Cadell; and J. Institutes of Natural and Revealed Religion. Johnson, Vol.

Joseph Priestley Discovers Different Kinds of Air 1774

I, , Vol. II, , Vol. III, Essay on the First Principles of Government ; and on the nature of political, civil, and religious liberty. Remarks on some paragraphs in the fourth volume of Dr. Blackstone's Commentaries on the laws of England, relating to the Dissenters.


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Johnson and J. Payne, Proposals for printing by subscription, The history and present state of discoveries relating to vision, light, and colours. Leeds: n. Directions for impregnating water with fixed air; in order to communicate to it the peculiar spirit and virtues of Pyrmont water, and other mineral waters of a similar nature. Robert C. Sleigh, Jr. New Haven: Yale University Press , xxxviii, New York: W. Norton , Leibniz: Determinist, Theist, Idealist.

New York: Oxford University Press , 10—13, 1—20, 41— Letter to a Layman, on the Subject of the Rev. Lindsey's Proposal for a Reformed English Church. Wilkie, Experiments and Observations on Different Kinds of Air. London W. Bowyer and J. Nichols, — There are several different editions of these volumes, each important. Philosophical Transactions 65 : — UK Sunday Telegraph.

Archived from the original on 29 October Retrieved 8 July Gibbs, —40, ; Uglow, —20, ; Jackson, —28; Holt, — American Academy of Arts and Sciences. Archived PDF from the original on 15 May Retrieved 28 July An History of the Corruptions of Christianity. The importance and extent of free inquiry in matters of religion: a sermon, preached before the congregations of the Old and New Meeting of Protestant Dissenters at Birmingham.

To which are added, reflections on the present state of free inquiry in this country. Birmingham: Printed by M. Swinney; for J. Johnson, London, A letter to the Right Honourable William Pitt, Debrett, Birmingham: Printed by Thomas Pearson; sold by J. Chemical Heritage Magazine. Archived from the original on 12 January Retrieved 1 January Archived from the original on 3 March Retrieved 11 June Thompson; sold by J.

Truman; McEvoy, John G. Boston, Mass. Archived from the original on 3 June Archived from the original on 24 June Retrieved 21 June Archived from the original on 24 December Retrieved 23 December See Rutt, XXV, Priestley in America, taken on board of a neutral vessel London, In France, to avoid arrest as an Englishmen, he assumed the name of Jean Martin, and lived quietly at Passy.

John G. Alger , Englishmen in the French Revolution London, , Tony Rail, op. A General History of the Christian Church. Northumberland: Printed for the author by Andrew Kennedy, His original headstone gives his age as "LXXI" Archived from the original on 23 December Retrieved 17 November See also page of Walker, William H. Journal of Chemical Education. Bibcode : JChEd Joseph Priestley College.

Archived from the original on 14 November Dictionary of Minor Planet Names. Berlin and New York: Springer , Williamson , unveiled in There are Blue Plaques commemorating him on the side of the Church of St. Michael and St. Dickinson College.


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  • Archived from the original on 5 January Retrieved 8 February Joseph Priestley and the Discovery of Oxygen. American Chemical Society. Archived from the original on 26 December Retrieved 12 November Lindsay, Jack, ed. Autobiography of Joseph Priestley. Teaneck: Fairleigh Dickinson University Press, Miller, Peter N. Priestley: Political Writings. Cambridge: Cambridge University Press, Passmore, John A. Priestley's Writings on Philosophy, Science and Politics.

    New York: Collier Books, Rutt, John T. London: George Smallfield, Life and Correspondence of Joseph Priestley. Schofield, Robert E. Cambridge: MIT Press, Gibbs, F. London: Thomas Nelson and Sons, Graham, Jenny. Transactions of the American Philosophical Society 85 Holt, Anne. A Life of Joseph Priestley. London: Oxford University Press, Jackson, Joe. New York: Viking, Johnson, Steven. Priestley also developed a critical method in his approach to scripture based on careful linguistic and historical study.

    He emphasized the highly figurative nature of the scriptures and argued that many misunderstandings were merely verbal, the result of taking ancient languages out of their cultural context. Furthermore, Priestley studied history in order to explain the ways in which Christianity had become corrupted over time as misunderstandings crept in, disfiguring the pure and simple beliefs of the early church.

    Application of his theological methods allowed Priestley to develop a set of religious beliefs which he regarded as highly rational and as close as possible to the pure Christianity of the early church. Already denying the Trinity, Priestley left Daventry Academy an Arian and tells us that it was after reading Nathaniel Lardner's Letter on the Logos ofthat he adopted the Unitarian creed he held for most of his adult life.

    Priestley argued that the notion of the Trinity is an essentially irrational tenet of an unquestioning faith. It requires a willingness to replace individual reason with trust in the teaching of church authorities whose power is perpetuated by ideas shrouded in superstition and mystery. He compared this belief to the simple idea of a unified God, a rational truth present in both natural and revealed religion. His historical work allowed Priestley to argue that the early Christians and Church Fathers were Unitarian and that belief in the Trinity was a corruption that had crept into scripture over the centuries.

    Joseph Priestley, Scientist, Philosopher, and Theologian - Oxford Scholarship

    The Trinity slowly developed over time as gentile and heathen beliefs infiltrated simple "pristine" understanding of the unlearned. The most important message of the Old Testament, argues Priestley, is that God is unified and indivisible. In the New Testament, while the role of Jesus is essential, the Father is entirely exclusive of the Son. He tells us that when scripture appears to say that the Father, Son and the Holy Spirit are equally divine, the language is highly figurative and should not be read literally.

    This leaves Jesus as wholly human and the powers he possessed as those granted by God to an ordinary man. Christ has the power for resurrection and ascension, but he is not God, according to Priestley. He is not divine and should not be worshipped, despite being an object of our utmost respect. Priestley undermined the divinity of Jesus and in doing so deeply altered the whole interpretation of his death and resurrection. Priestley insisted that the death of Jesus was only a sacrifice in the figurative sense.

    His death was not a means by which the wrath of God had been diverted, and his sacrifice was not an atonement for sin. Jesus was not a divine mediator between God and humanity; he was a savior simply because his life was a demonstration of perfect moral duty and the truth of physical resurrection. Priestley argued that the Calvinist notion of predestination was irrational and had only a flimsy basis in scripture.

    Arguing from utilitarian premises, Priestley writes that God's manifest plan is to produce the greatest happiness for his people; a system which condemns many to eternal torment and therefore produces exceptional misery cannot be part of this plan. Priestley was drawn to the idea of universal salvation, the only system to ensure the greatest happiness. He acknowledged the role of punishment as an important part of divine justice and even wrote that it should be long and severe in order to be effective.

    However, he could not accept that finite humans would be punished infinitely. The notion of grace that was prevalent among the clergy and orthodox believers was based on the idea of original sin pardoned by the death of Christ, a sacrifice for the sake of fallen humankind. Instead of believing in this idea of innate sinfulness and supernatural reconciliation, Priestley held that everyone had the potential to attain the perfect moral knowledge that Jesus had exemplified and taught. Part of this potential for perfection, writes Priestley, is that God has given us moral laws that we are perfectly capable of following.

    Although he concedes that everyday fallible humans are unlikely to be morally perfect, he contends that we can choose to lead a life pleasing to God and make constant effort to repent and change our behavior. He places this at the center of Christian life, rather than the emotional evangelical faith, the Calvinist "experience" or the fallacy of the death bed conversion. He tells us that it is not arrogance or pride which allows us to dismiss the idea of original sin and believe that all humankind can do what God tells us.

    It is simply the power that God has given to all of us.

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    The idea that we are justified by faith or predestination diminishes this power that every person has to do the will of God. The metaphysical basis for Priestley's disavowal of the existence of the soul is explored in the section of this article on "Matter and Spirit. He writes that there is no scriptural basis for a split between body and soul. Not only is belief in the soul unreasonable based on the evidence around us, writes Priestley, it is also a belief which careful historical exploration shows was an idolatrous heathen tenet that crept into Christianity and slowly corrupted it.

    Priestley was a fervent millenarian, trusting in biblical prophecy and waiting for the second coming of Christ. He read widely on the millennium and placed himself within a well established scholarly tradition of millenarian study. Priestley was hopeful that he was living in the "last days" before the foretold return of Christ. Reading Daniel and Revelation, Priestley believed that the return of the Jews to their homeland would precede the glorious second coming and waited eagerly for such an event.

    He carefully watched worldwide political developments for signs that Christ's rule on earth was soon to begin, and it is likely that looking for such evidence that the bible contained absolute truths and tangible proofs of the existence of the deity appealed to Priestley's scientific mindset. The American Revolution seemed a good sign and his optimism intensified after the French Revolution and the Birmingham riots.

    At the end of his life Priestley became increasingly preoccupied with the millennium, putting a great deal of hope in the imminent arrival of Christ and studying scriptural prophecy in great detail. For Priestley there was an order, even a beauty, which stemmed from the process of obtaining truth through reason, and in the pure, rational and simple truth that this process revealed.

    Although his enemies called him "gunpowder Joe," his grains of gunpowder were no more than a series of necessarilyrelated ideas which, when marshaled by strict reason and controlled by rational thought, would always have the same outcome. However, to some of Priestley's Anglican opponents his reason-driven truth was subversive and seditious. He was accused of demolishing the foundations of revealed truth and, in consequence, of morality. They saw moral upheaval where Priestley saw rationality and order. Contemporary reactions to Priestley's theological and religious works often involved in-depth scriptural analysis.

    This kind of discussion has been seen as less relevant today. Some secondary comment has focused on the interaction between Priestley's theological position and his political beliefs, often identifying interesting conceptual links. For example, J. Waterman has added to the debate, arguing that although challenging the Trinity is enough to undermine the principle of subordination in church and society, there is no necessary link between dissent and subversive politics Haakonssen Other comment has examined Priestley's belief in miracles and biblical prophecy in light of his highly rational stance.

    For example, Martin Fitzpatrick asks us to consider whether Priestley's obsession with apocalyptic texts in his later life was the sign of an unbalanced mind Fitzpatrick However, Clark-Garrett argues that, far from a weakness or drift in old age, Priestley's millenarian speculations were consistent with his overall outlook. His attention focused by the French Revolution, Priestley was simply using his scientific method to observe the unfolding patterns of Providence, and the fulfilment of prophecy was a key part of this search for facts and evidence to bolster his rational religion At the heart of Priestley's political philosophy lie the twin themes of progress and perfectibility.

    His work is shot-through with an optimism that arises from his unswerving belief in progress and a perfect future state. Priestley's work rests on an assumption that humankind will be better off in the future than it is at present and that society in the present is already more perfect than life in the past. Unlike brute animals who continue in the same way without change, human society is constantly in a state of development, change and improvement.

    He tells us of the happiness he experiences because of the realization that whatever the world was like at the beginning the end will be perfect and "paradisiacal. Priestley conjectures a social contract to illustrate his ideas on liberty. He tells us of a group of unconnected individuals who lead separate lives.

    They are exposed to many wrongs and have few advantages. If the people voluntarily submit to join forces as part of a group they resign some of their natural liberty in return for protection, alliance and other advantages. Some liberty has to be given up just for the society to function. A large group of people would need representatives in order to make decisions on behalf of society and, although this may seem like a sacrifice of liberty, these men would act purely for the good of society and reflect the sentiments of the whole body. The only thing that gives them power is that they are there to act for the public good.

    Reason and conscience guide them and the people judge them. Significantly, Priestley divides "natural" liberty into civil and political liberty after the contractual agreement. This is a distinction which Robert E. Schofield says was only commonplace after Mill and that Priestley felt was necessary for the sake of clarity Political liberty, Priestley tells us, is the power of holding or electing public office.

    It is the "right of magistracy," the power of the private opinion made public. Civil liberty is the power an individual has over their actions and only refers to their own conduct. It is the right to be exempt from the control of others. Priestley tells us that when natural liberty is resigned upon entering into society, it is civil liberty that is relinquished for the sake of increased political liberty. Once elaborated, Priestley's articulation of two types of liberty allows him to place his theory on utilitarian grounds.

    The good and happiness of the whole of society is made identical with the good and happiness of the majority of its members. Happiness, good and progress become inextricably linked within this theory, as Priestley had insisted that progress towards perfection is the ultimate goal for mankind and would result in unbounded happiness.

    He tells us that government is required to identify what is most conducive to progress, and therefore to happiness, and to eradicate barriers and limits to progress. For example, division of labor is useful and should be encouraged, as it aids the economy and increases knowledge. Specialization helps everyone reach their potential and means that the arts and sciences are likely to flourish.

    Meanwhile, progress is hindered by encroachments on civil liberty. Priestley was concerned that progress would stagnate if education and religion were not left free to flourish and reach perfection. He wrote against established religion and against state education, wary of uniformity and unnecessary authority. He insisted that diversity of opinion was essential for free debate and ultimate progress and therefore advocated complete religious liberty and freedom of speech. Although Priestley celebrated freedom and was concerned to limit government intervention for the sake of individual liberty, he did not have an antagonistic opinion of the law.

    Good government plays an important role within Priestley's philosophy, protecting liberty and rights but also serving as an active agent of change. Priestley's political philosophy has a psychological foundation based on the doctrine of association. Human perfection was to be achieved along associationist lines. Good government and society was crucial to this process. Government should explore what circumstances are most conducive to progress and happiness and apply these principles, even if this means intervening or limiting freedom to some extent.

    Priestley's theology and his status as a dissenter informed much of his political work. At a political level Priestley was keen to speak on behalf of rational dissent and outline the political principles most often associated with Protestant dissent in general. Eager to inform the Anglican clergy of the political opinions to be found amongst their dissenting counterparts, Priestley writes that there is no reason to assume that dissenters are anarchists or republicans. The vast majority are peaceful, law-abiding and property-owning.

    He tells us that dissenters respect human authority in most matters, respect the government and support the Hanoverian succession. However, they do not recognize human authority in religion, seeing no spiritual or scriptural reason for church authority or established religion. The church has no business in civil government, and one of the many reforms required was a full separation of church and state, as well as a purging of other popish ways still left within the Church of England.

    At a philosophical level, Priestley's demands for religious liberty were often for utilitarian reasons, recognizing the need for liberty in order to foster truth and aid progress. He was skilled in illustrating these abstract arguments with numerous historical examples to consolidate his case. Priestley did believe firmly in the absolute nature of divine truth, but he argued for full toleration for dissenters, Catholics and even atheists.

    This was because at the root of his call for toleration was a powerful conviction that to uncover divine truth should be the ultimate aim of all human endeavors, and this needed an atmosphere of free and unrestrained debate. Rational dissent held that truth arose from the application of human reason and conversely that unnecessary intervention could be extremely harmful. If laws were in place that stifled free discussion and forced belief in superstition or falsehood, the cause of truth was left in the dark. Priestley's Essay on the First Principles of Government went swiftly through two editions and continued to be published throughout the nineteenth century.

    Clearly influential at the time, the work also had significant long-term impact. Jeremy Bentham acknowledged the Essay as the inspiration for his utilitarian "greatest happiness" principle. Although Bentham's famous words do not appear anywhere in the work of Priestley, it is fair to say that this is a significant legacy. However, in his own time, Priestley's work was met with criticism and attack. Priestley backed the campaign for the repeal of the test and corporation acts, and this provoked a huge conservative backlash fuelled in part by heightened reactionary fears following the French revolution.

    In this heated atmosphere, accusations of sedition and treason were common currency, and Priestley came under serious criticism for his political and theological views. Priestley's critics entangled religion and politics and made little attempt to identify Priestley's own first principles. Priestley was accused of attempting to undermine the authority of the church and the government. His political philosophy seemed dangerously egalitarian and his insistence on continual progress was a dangerous threat to the old order.

    Priestley's insistence on the importance of unfettered individual reason had dangerous consequences. His enemies explicitly stated that Priestley's concern for the truth had inverted the order of things. Priestley had destroyed the necessity for a separate Clergy and attacked the sacredness of their profession. By questioning the need for obedience and asserting the authority of the individual, it seemed to nervous minds that he had inverted the whole social hierarchy. One way this division has manifested itself is in the interesting relationship between natural law and utility as it appears in Priestley's political philosophy.

    Schofield suggests that Priestley's brand of utilitarianism is significantly less relativist than Bentham's. While Bentham used the happiness principle as the only guiding force of government, Priestley never doubted that there was a perfect way of governing and that it was towards this that mankind should progress. Canovan also questions the idea that Priestley was a proto-Benthamite. She says that the underlying assumptions of the two men are significantly different. Priestley firmly believed in the existence of a benign and all powerful God who presided over a well-ordered and structured universe.

    So it was in this realm of natural law that Priestley's utilitarianism was supposed to operate. Priestley believed in the existence of an objective moral order so while happiness for Bentham could be whatever society or any individual decided it should be, happiness for Priestley was universal, fixed and could be evaluated in moral terms.

    While Bentham constructed a moral order from utilitarian grounds, Priestley simply used the principle in order to evaluate and discern moral laws. This places Priestley firmly in the natural law tradition. It allows him to use the language of rights as part of his political philosophy without compromising his utilitarianism. The real extent of Priestley's liberalism is debated in a variety of different ways in the secondary literature. For example, Martin Fitzpatrick has highlighted that, while Priestley supported toleration whole-heartedly, this was because of his conviction that absolute truth would eventually prevail, rather than the pluralistic outlook of Richard Price Margaret Canovan has pointed out that, although Priestley is rightly remembered as a liberal, he often celebrated a paternalistic view of class relations Celebrating the bourgeois station, he stressed the importance of middle class charity to the poor, which would encourage their ambition and create useful social bonds.

    He also wrote that inequalities were part of God's plan for the present, despite his general support for social mobility. Kramnick argues that the scientifically minded Priestley viewed the state as a kind of laboratory where intervention was required to perfect humankind, and so his thought is shot-through with a regard for authority and discipline 11, The principle of association states that ideas are generated from external sensations.

    Complex ideas are made up of simple ideas. These complex ideas are formed through repeated juxtaposition or "association" over time. This means that ideas become united in the mind so that one idea will be invariably followed by the other. Hartley tells us that this principle has not escaped the notice of writers both ancient and modern but that it was John Locke who affixed the word "association" to the theory.

    Locke had argued that ideas are not innate but derived from experience. In mechanistic terms he explained the ways in which simple ideas become associated in experience and therefore build up complex ideas. Locke had posited a mind blank before experience of sense impressions had made their mark. Hartley picked up this idea and added to it a physiological basis for the associationist theory, an idea that it was vibrations acting on the brain that laid down ideas and that when two vibrations occurred simultaneously over time they become associated in the mind.

    Hartley used Locke's epistemology but removed Locke's emphasis on reflection as a means to knowledge. Locke had written that all knowledge is based on sensation and then reflection. Hartley simply said that all types of ideas were derived from sensation. Priestley followed Hartley and dropped Locke's need for reflection as a distinct source of knowledge. Priestley also read the Rev. John Gay who had used Locke's associationist principle to argue against the innatist theory of morals of Francis Hutcheson.

    Gay had argued that morality and the passions were acquired through experience; as we attempt to avoid pain and seek pleasure our morals and passions are formed. Enjoying debate and finding creativity in opposition, Priestley expounded his most coherent theory of association as an attack on the notion that innate common sense can stand above reason when it comes to religious belief. Published in Priestley's Examination of Dr. Reid ' s Inquiry Beattie ' s Essay Oswald ' s Appeal is a harsh and rigorous refutation of common sense in favor of association.

    Like Hartley, Priestley was keen to make association the sole basis of human understanding. Hobbes had written of association as one means that certain ideas become linked by resemblance or causality. In contrast to Hobbes, Locke was more interested in unnaturally associated ideas, or when two things that have nothing in common end up united. However, for Priestley association was the foundation and excluded all other epistemological sources.

    This certainly ruled out what he took to be Reid's theory, that sensations are made into ideas by innate principles implanted by God, and it excluded the argument that sensations act on the passive matter of the brain and that innate instincts act to turn them into knowledge. Priestley writes that living is about experience.

    That something seems instinctive does not mean that it has not derived ultimately from external experience. Associationism allowed Priestley to identify the general laws of human nature he was looking for and is therefore the basis for much of his metaphysical, educational and political writing, as well as informing his theology. For example, Priestley's work on the nature of matter enabled him to add a physiological basis to the doctrine of association. Once association was understood physiologically Priestley was able to argue against Cartesian dualism, against the existence of an immaterial soul, and in favor of the material unity of body and mind.

    In his political and educational philosophy the doctrine of association furnished Priestley with a means by which circumstances could be understood to shape the intellectual and moral life of individuals. This allows for progress in society and in the acquisition of knowledge because it allows for controlled change through experience. It gives teachers and legislators the power to shape others through altering circumstances or environment. Association consolidated Priestley's determinist doctrine of philosophical necessity as it allowed all actions to be traced back to motives and ideas formed entirely from experience and therefore potentially determined by Providence.

    Finally, association also appears in Priestley's theology. In the Institutes of Natural and Revealed Religion Priestley explains that revealed religion has followed the same pattern historically as an individual does when learning through association. The development from the Old Testament to the New is like the process of acquiring knowledge of pain and difficulty but also love of god and the pleasures of life as an individual.

    Priestley's devotion to the doctrine of association was one of the less controversial aspects of his thought. The system was already part of a respected tradition and Priestley's ideas were not especially innovative or shocking. However, the polemic feel of his attacks on Reid, Beattie and Oswald did provoke some sharp replies and Priestley actually issued an apology for the tone he had struck.

    Robert E. Schofield has argued that Priestley played a crucial role in maintaining Hartley's ideas, especially among the utilitarians, and therefore had an important influence on the nineteenth century. While late nineteenth-century associationist psychology is often regarded as the precursor to the behaviorism of the twentieth century, studying Priestley allows us to locate the ideas considerably further back Priestley wanted to elucidate a physiological theory to refute his interpretation of the Scottish "common sense" system of separate instinctive perceptions.

    Priestley writes that all sensations are the same. They arise from experience as vibrations in the brain. Priestley argued that this system offered a simplicity that the theory of separate and original instincts could not. An outside stimulus causes the brain to vibrate. For example, "seeing" is actually the result of vibrations of the optic nerve caused by light.

    Vibrations consisted of tiny movements of small particle, of the nerves and then of the brain. These movements were caused by the impressions made by external objects on any of the five senses. Priestley tells us that all matter vibrates and that all matter can transmit these vibrations to our brains.

    Following Hartley, Priestley tells us that once the brain has been made to vibrate a trace of that vibration is left behind. Hartley calls this a "vibratiuncle. A "vibratiuncle" is laid down as a tendency for the brain to vibrate the same way again. If the initial vibration was strong or intense, then so too will be the vibratiuncle. If the vibration is weak or small, then the vibratiuncle too is weaker. If the vibration occurs many times, this has the same affect, strengthening the trace and increasing the tendency to vibrate.

    When two vibrations occur together they act on each other or modify each other so that, as they occur repeatedly together, they become associated in the brain. This association means that when one occurs the other will also occur.

    Joseph Priestley (1733—1804)

    Vibrations can build up sets of vibratriuncles so that if only one vibrates, the others in the system will vibrate too. One occurrence triggers all of them. This is the physiological basis of the associationist doctrine. It explains how sensations become ideas and how simple ideas can build up into complex ones through this process. While Hartley did acknowledge the parallel process between ideas and physiological vibrations, he was keen to leave room in his theory for the existence of an immaterial soul. Priestley lacked his caution and was driven to question the means by which a non-physical substance could act upon a physical one.

    While Hartley had left this a mystery and posited an "elementary substance" that was neither matter nor spirit but linked them both, Priestley's answer was to abandon any kind of dualism at all. He writes that our understanding is troubled simply because of the way in which matter appears to us. Superficially it seems solid and inert. However, Priestley tells us, experiments reveal that this is not the case.