History and Philosophy in the Classroom Joseph Priestley and the Discovery of Photosynthesis

There are three important social and educational considerations that justify
dealing with Joseph Priestley in school science programmes:
• First, schools are asked to address pressing environmental problems and
especially the ‘goodness of air’ (to use Priestley’s phrase) and, thus, they
need to teach about the process of photosynthesis, something on which
Priestley shed so much early understanding.
• Second, NOS goals are included in numerous international curricula, and
Priestley’s writings and practice well illustrate many of the essential
features of NOS.
• Third, there is a widespread concern in education and in culture with
reappraising and re-examining the tenets of the European Enlightenment
tradition, and in particular its universalist, naturalist and secular commitments. Michael Peters, quoted earlier, well captures this widespread
concern (Peters 1995, pp. 327–328). Priestley’s life and achievements
provide a good case for evaluating what is dead and what is living from
the original Enlightenment claims and achievements.
Priestley made significant contributions to all three areas, and, pleasingly,
he wrote simply and engagingly, with ‘the public’ in mind; he wrote in such
a way that readers could themselves experiment and observe as he was doing;
he might be considered the first advocate of ‘science for all’. So, infusing
historical and philosophical dimensions into this standard curriculum topic
allows, not just the content of science to be learned, but also important things
about science, about important contributors to its history, and, consequently,
the nature of science can be better appreciated.
Photosynthesis is a fundamental process for life on earth, with many
biologists rating it the most important natural process; as such, it has long
been a core part of the school biology curriculum. However, it is well known
that children at all levels have great difficulty comprehending and understanding photosynthesis: students’ conceptual understanding of the process
routinely lags behind what might be anticipated from their grade level and
from the curriculum they have been taught.2 Given the current, well-publicised
environmental problems concerning the state of the atmosphere, carbon
Chapter 7
trading, CO2 emissions, greenhouse gases, forest preservation and so on, then
correcting the inadequate student and general public knowledge of such a
fundamental natural process becomes more pressing.
The science part is tied up with two basic, complementary processes:
photosynthesis3 and respiration:
Photosynthesis: carbon dioxide + water + energy (light) → organic compounds
(starch) + oxygen
Respiration: organic compounds + oxygen → carbon dioxide + water + energy
The first process represents both ‘carbon capture’ and the restoration of
air; when buried coal seams are dug up, or forests are cut down and burned,
there is massive carbon release via the second process. The two processes are
major components of the Earth’s ‘carbon cycle’. Clearly, it is important for
students to learn about these processes and their wider social, economic,
cultural and ethical dimensions and impacts. This is part of responsible
citizenship. However, additionally, there is great value in learning about how
these fundamental processes came to be discovered and understood; such
learning provides appreciation and understanding of the nature of science and
the scientific enterprise.
As was mentioned in Chapter 2, Priestley was one of the foremost scientists
(natural philosophers) of the eighteenth century, he was a lifelong devout
Christian minister and he was an energetic exponent of Enlightenment
principles. In particular, Priestley advocated: the application of the methodology of the new Newtonian science to all fields of enquiry – historical,
theological, educational, ethical; the separation of Church and state; freedom
of speech; freedom of religion; decriminalisation of religious belief and
practice; and the freedom of science (including historical studies of religious
scripture) from political and religious control. As with Locke, Kant, Rousseau
and all Enlightenment figures, he was a ceaseless advocate of education and,
specifically, of what would now be called ‘science education’.4 Thus, the
teaching of photosynthesis, with attention to the historical and philosophical
dimensions of Priestley’s life and work, allows each of the above current
educational concerns to be productively addressed.
Some Appraisals of Priestley
Modern appreciation of Priestley has been blighted by the harsh and unfair
judgement of Thomas Kuhn in his best-selling Structure of Scientific Revolutions (Kuhn 1970). In a famous passage, Kuhn writes of the irrationality of
paradigm change and of old paradigms just dying out until, ‘at last only a
few elderly hold-outs remain’. He then singularly names Priestley as an
example ‘of the man who continues to resist after his whole profession has
been converted’ and adds that such a man ‘has ipso facto ceased to be a
scientist’ (Kuhn 1970, p. 159). This outrageous charge ‘blackened’ Priestley’s
reputation in the academic world; Kuhn’s has become the widely accepted
History and Philosophy: Joseph Priestley 271
obituary for Priestley – the stubborn old man who held on to belief in a
peculiar phlogiston substance and who resisted the dawning bright light of
Lavoisierian chemistry. Pleasingly, some historians and philosophers have
provided extensive studies that refute Kuhn’s caricature of Priestley, but,
unfortunately, their work is not translated into more than twenty languages,
nor set as class reading in countless thousands of courses, nor read by millions.
A more generous and accurate assessment of Priestley was given by Frederic
Harrison, in his Introduction to a nineteenth-century edition of Priestley’s
Scientific Correspondence, as follows:
If we choose one man as a type of the intellectual energy of the eighteenth century,
we could hardly find a better than Joseph Priestley, though his was not the greatest
mind of the century. His versatility, eagerness, activity, and humanity; the immense
range of his curiosity in all things, physical, moral, or social; his place in science,
in theology, in philosophy, and in politics; his peculiar relation to the Revolution,
and the pathetic story of his unmerited sufferings, may make him the hero of the
eighteenth century.
(Bolton 1892, Introduction)
Priestley’s Life
There has been a good deal written about Priestley’s life and accomplishments
that teachers can draw on for elaborating contemporary lessons.5 Priestley
was born in Yorkshire in 1733 and died on 6 February 1804 in the United
States, in the small, isolated backwoods town of Northumberland in the state
of Pennsylvania. Although the bicentenary of his death was rightly marked
in historical and chemical circles, it unfortunately went unnoticed in education
circles. This is a pity, as Priestley was a dedicated teacher, educationalist and,
perhaps, the first modern science teacher. As well as teaching, preaching
and researching, Priestley wrote a number of influential works on the theory
and practice of education.
Priestley had a severe and disturbing Calvinistic upbringing.6 In his late
teenage years, being a religious dissenter and, hence, barred from Oxford and
Cambridge universities, he attended Daventry Academy, where, as a teenager,
he read Locke, Newton, Hartley and many of the major philosophical,
scientific and religious works of the time. It was an institution where the
‘serious pursuit of truth’ was the preoccupation (Priestley 1806/1970, p. 75).7
This was in marked contrast to the scholarly climate in the established
universities.8 He acquired fluency in Greek, Latin, Syriac and a number of
European languages, including, later, High Dutch.
At 22 years of age, he was ordained a Dissenting minister, the duties of
which vocation were the central preoccupation of his adult life. He ministered
in a number of small rural towns, where he also established schools, being
perhaps the first ever teacher of science to engage students in laboratory work
(Schofield 1997, p. 79). In his late twenties, he taught language, history, logic
and literature at the Warrington Academy, where he also began reading
272 History and Philosophy: Joseph Priestley
contemporary works in chemistry and electricity that supplemented his earlier
readings of Newton’s optics and astronomy.
At age 34 years, he was called as minister to the Presbyterian Chapel in
Leeds, which was a centre for Yorkshire’s newly born and thriving commercial
and industrial life. He left Leeds and worked for 5 years as a secretary and
children’s tutor for Lord Shelburne, a prominent liberal English politician who
negotiated the Treaty of Paris that ended the American Revolution. During
this employment, he travelled in Europe, famously meeting, in October 1774
in Paris, with Antoine Lavoisier, with whose name Priestley’s has ever since
been entwined, because of controversy over the discovery of oxygen and
Priestley’s dogged refusal to accept the latter’s ‘new’ chemistry.9 Priestley
lent support to the American and French Revolutions, seeing both of them
as the victory of liberty and freedom over the stultifying, autocratic power of
the established church (be it Roman Catholic in the ancien régime of France,
Anglican in the United Kingdom or Lutheran in Germany and Scandanavia)
and state.10 He publicly rejected Trinitarian belief, notwithstanding that such
denial was a capital offence at the time, and founded the Unitarian sect. In
detailed publications, he argued that the Church’s triune doctrine was the
product of Hellenistic philosophical corruption of the early Christian church
(Priestley 1786). Newton, of course, held the same position, but never
advertised the matter; Priestley’s liberalism, and ultimately his epistemological
convictions, led him to very public affirmation of Unitarianism: truth emerges
from dispute and defence of positions.
England was never a comfortable place for supporters of the 1789 French
Revolution, and it was distinctly less so after the initial ‘middle-class’ revolution gave way to the Paris Commune in 1792, and after England joined the
counter-revolutionary, reactionary coalition in war against France in 1793. So,
at age 61 years, after his laboratory and library were destroyed by an enraged
‘King and Church’ reactionary mob, and after various close dissenter friends
and political liberals were transported as convicts to Botany Bay, Priestley fled
England in 1794 and travelled to Northumberland in a remote rural corner
of Pennsylvania, where he spent the last decade of his life writing, ministering
and productively engaging with prominent politicians, especially Thomas
Jefferson.11 He died in 1804, in his own, still-standing home.12
Priestley’s Publications
Christian ministry was the most important thing in Priestley’s life, and he kept
affirming this, from his ordination in 1755 at age 22 to his death at age 70.13
However, along with his active clerical life, Priestley published an enormous
number of substantial and authoritative works across a wide range of fields:
these included over 200 books, pamphlets and articles on history of science
(specifically of electricity and optics), political theory, theology, biblical
criticism, church history, theory of language, philosophy of education,
rhetoric, as well as chemistry, for which he is now best known. Included in
this corpus are about twenty substantial, multivolume works, many of which
History and Philosophy: Joseph Priestley 273
went into second, third and fourth editions. Priestley’s Collected Works
(twenty-five volumes), which do not include all his scientific publications, are
in Rutt (1817–1832/1972). Some of Priestley’s scientific correspondence is in
Robert Schofield’s edited anthology (1966). The most accessible source for
a range of his major writings is still the 350-page anthology edited by John
Passmore (Passmore 1965).14
Priestley and the Enlightenment
Priestley’s life spanned the core years of the European Enlightenment, which
was inspired by the achievements and writings of the new science of Bacon,
Galileo, Huygens and, above all, Isaac Newton.15 Indeed, the whole Enlightenment began with the conviction of Newton, Locke, Hume and others that the
methods of the new science should be applied in the moral and political
sciences. Newton expressed the matter in his Opticks as follows: ‘If natural
philosophy in all its Parts, by pursuing this Method, shall at length be
perfected, the Bounds of Moral Philosophy will be also enlarged’ (Newton
1730/1979, p. 405).16 David Hume echoed this expectation with the subtitle
of his famous Treatise on Human Nature, which reads, Being an Attempt to
Introduce the Experimental Method of Reasoning into Moral Subjects. In the
Preface, he says he is following the philosophers of England who have ‘began
to put the science of man on a new footing’ (Hume 1739/1888, p. xxi).
At Daventry Academy, Priestley read Newton and Locke and their major
expositors and there began developing his particular variant of the Enlightenment worldview. He was a devout Christian, not a Deist believing in an
impersonal Creator or ‘Intelligent Designer’, who set the world going then
left it alone. He believed in a personal God and concurrently developed a
rationalist and materialist worldview that was consistently brought to bear
upon his scientific and other investigations and was in turn reinforced by these
Priestley was a polymath and, in current terminology, a ‘public intellectual’;
he had staggeringly wide interests, but, more than this, he explicitly sought
for coherence and intellectual unity in his scholarly, personal, religious and
political activity. Newton had established that the single law of attraction
applied on Earth and in the heavens. Priestley thought the same simplicity of
law would apply through the social and mental (psychological) realms as well;
this, in part, because there was only a single substance, matter, throughout
all realms. He was a forceful advocate of the materialist tradition in the
Enlightenment. He was an ontological monist, rejecting all dualisms in natural
philosophy, psychology and religion.17 He did not believe there were a
multiplicity of kinds of substance in the world: recourse to ‘imponderable
fluids’, including Lavoisier’s caloric, to explain magnetic, electric, optical or
heat phenomena, was both unnecessary (as they explained nothing, and the
phenomena could be explained by suitable movement of particles, as was
maintained by the atomists) and fanciful, as no such entities (non-material
274 History and Philosophy: Joseph Priestley
‘fluids’) existed. As he said of supposed electrical fluid: ‘there is no electric fluid
at all, and that electrification is only some [new] modification of the matter of
which any body consisted before that operation’ (Schofield 1966, p. 58).18
For Priestley, his epistemology (empiricism) related to his ontology
(materialist monism), and both related to his theology (Unitarianism) and to
his psychology (associationism). All the foregoing bore upon his political and
social theory (liberalism). He was a consciously synoptic or systematic thinker:
knowledge and life were a whole and had to relate consistently. Whether
Priestley achieved the coherence he sought has been a matter of considerable
debate. From the very outset, many have disputed the coherence of Priestley’s
claimed conjunction of ontological materialism and Christian belief. Aiming
for coherence and arriving at it are, of course, two different things.
Priestley was committed to a Christian worldview that was informed by
natural philosophy. The worldview is developed throughout his work; one
partial expression is in the Preface to his History of Electricity:
A philosopher [scientist] ought to be something greater, and better than another
man. The contemplation of the works of God should give sublimity to his virtue,
should expand his benevolence, extinguish every-thing mean, base, and selfish in
his nature, give dignity to all his sentiments, and teach him to aspire to the moral
perfections of the great author of all things. . . . A life spent in the contemplation
of the productions of divine power, wisdom, and goodness, would be a life of
(Priestley 1767/1775, Preface)
With such a worldview, the pursuit of what we now call ‘scientific’ know –
ledge was a religious virtue, indeed almost a religious obligation: to ignore
the world was to ignore God’s handiwork; to find out about the world was
to give respect and honour to God. Certainly, there was a religious obligation not to thwart the advance of knowledge, not to stand in the way of, or
suppress, truth. And, as authoritarianism and absolutism were antithetical to
the pursuit of truth, both had to be opposed, in churches and states. For
Priestley, religion and epistemology were combined or codependent. Contrary
to many popular present-day views, for Priestley, religious knowledge was not
a different kind of knowledge with a different epistemology; he was not an
eighteenth-century exponent of ‘non-overlapping magisteria’ (NOMA).
Priestley’s First Steps Towards the Discovery of
Priestley did not begin serious chemical studies until his early 30s, during his
ministry at the Leeds Presbyterian Chapel (1767–1773). In quick succession,
by utilising a new method of collecting ‘airs’ over water and mercury, and by
utilising a new and massive burning lens as a source of heat,19 Priestley created,
isolated and listed properties of a dozen or more of the major ‘airs’.
History and Philosophy: Joseph Priestley 275
The 1772 Royal Society Talks
The experiments and investigations of airs, conducted in Leeds by Priestley,
were announced to the scholarly world in a series of talks he delivered to the
Royal Society in London, in March 1772. The talks subsequently were
published as his famous 118-page paper in the Society’s Philosophical
Transactions of the same year – ‘Observations on Different Kinds of Air’
(Priestley 1772a).20 This paper was translated into many European languages;
it was widely read, including by Lavoisier; and, in 1773, it was awarded the
coveted Copley Medal of the Royal Society – the eighteenth-century equivalent
of the Nobel Prize.21 The paper was elaborated, with further experiments, in
his three-volume Experiments and Observations on Different Kinds of Air
(Priestley 1772b). These publications established Priestley as the undisputed
‘father of pneumatic chemistry’.
On 21 February 1770, he wrote to his lifelong intimate friend and fellow
Unitarian Theophilus Lindsey (1723–1808) that, ‘he was now taking up some
of Dr. Hale’s inquiries concerning air’ (Schofield 1997, p. 237). As he wrote
in his Royal Society address:
The quantity of air which even a small flame requires to keep it burning is
prodigious. It is generally said, that an ordinary candle consumes, as it is called,
about a gallon in a minute. Considering this amazing consumption of air, by fires
of all kinds, volcanoes, etc. it becomes a great object of philosophical inquiry, to
ascertain what change is made in the constitution of the air by flame, and to
discover what provision there is in nature for remedying the injury which the
atmosphere receives by this means. Some of the following experiments will,
perhaps, be thought to throw a little light upon the subject.
(Priestley 1772a, p. 162)
Priestley’s Christian worldview motivated this quest: with centuries of animal
and human respiration, plus volcanoes and natural fires, the atmosphere
should be progressively rendered unfit for human life, but there were
theological reasons why this could not happen. A beneficent, all-powerful
Creator would not design such a world; God must have made some provision
for the natural restoration of air.
Priestley’s first thought, or hypothesis, was the common-sensical one: as air
is necessary both for animal and vegetable life, then both animals and plants
must process air in the same manner. However, experiment led him to reject
this idea. As he wrote:
One might have imagined that, since common air is necessary to vegetable, as
well as to animal life, both plants and animals had affected it in the same manner,
and I own that I had that expectation when I first put a sprig of mint into a glass
jar standing inverted in a vessel of water; but when it had continued growing there
for some months, I found that the air would neither extinguish a candle, nor was
it at all inconvenient to a mouse, which I put into it.
(Priestley 1772a, p. 162)
276 History and Philosophy: Joseph Priestley
Priestley’s investigations bore fruit and, on 23 August 1771, he wrote again
to Lindsey saying: ‘I have discovered what I have long been in quest of, viz.,
that process in nature by which air, rendered noxious by breathing, is restored
to its former salubrious condition’ (Schofield 1966, p.133). In his Royal
Society address, Priestley said:
This observation led me to conclude, that plants, instead of affecting the air in
the same manner with animal respiration, reverse the effects of breathing, and
tend to keep the atmosphere sweet and wholesome, which it had become noxious,
in consequence of animals living and breathing, or dying and putrefying in it.
(Priestley 1772a, p. 166)
Priestley did suggest a mechanism for the beneficent effect: ‘this restoration
of vitiated air is affected by plants imbibing the phlogistic matter with which
it is overloaded by the burning of inflammable bodies’ (Priestley 1775–1777,
Vol.1, p. 49), but, in keeping with his strict epistemological principle of only
giving cautious or provisional status to conjectured, unseen mechanisms, he
added, ‘whether there be any foundation for this conjecture or not, the fact
is, I think indisputable’ (ibid.). His distinction between observational facts,
upon which there could and should be agreement, and unseen, putative
mechanisms was a fundamental one for Priestley. The distinction appears
many times in his writings. For example, in a 1779 letter to Giovanni Fabroni
concerning plants thriving in inflammable air, he says: ‘The facts appear to
me to be rather extraordinary. You must help me to explain them, for I am
a very bad theorist’ (Schofield 1966, p. 171). His insistence on the distinction
between fact and interpretation was such that he has sometimes been called
a ‘proto-positivist’. The philosophical issue has long been whether the ‘facts
of the matter’ can be articulated or described without recourse to theory.
The 1772 paper is a tour de force and justly known as a landmark in the
history of science. It describes Priestley’s manufacture of soda water (Pyrmont
water); his creation, but not recognition, of oxygen by heating saltpetre
(potassium nitrate); his nitric oxide test for the ‘goodness of air’; and, last but
not least, his identification of the mechanisms for the restoration of ‘the
goodness of air’. Any one of these achievements singularly would probably
have earned him the Copley medal.
Testing the Goodness of Air
An important step towards understanding the process of restoration of air by
plants (photosynthesis) was having some quantitative test for the ‘goodness
of air’. Without such a test, it was akin to saying that some treatment made
something heavier, or longer, without scales or tapes to indicate just how much
heavier or how much longer. Priestley’s novel nitrous air test provided such
a quantitative instrument.
Priestley took a given volume of insoluble, colourless nitrous air, mixed this
with double its volume of insoluble, colourless common air, waited for the
History and Philosophy: Joseph Priestley 277
reaction that formed soluble, brown nitrous vapour to take place, then shook
the resultant air over water and measured how much was dissolved by noting
the rise in water level in the collecting jar. In modern terms, the nitrous air
(NO) was combining with oxygen (O2) in the air to form the red, turbid and
soluble nitrogen dioxide (NO2). The more the water rose, the more oxygen
had been consumed, and, hence, the better the ‘goodness’ of the air in the
sample. This was his famous, and much used, Nitrous Air (nitric oxide, NO)
Test for the goodness of air (Boantza 2007, pp. 513–516).
Priestley’s Final Steps Towards Photosynthesis
When Priestley left Leeds in 1773 to begin work as a librarian, companion
and child’s tutor for Lord Shelburne, he had put into place a good many pieces
of the ‘restoration of air’ puzzle. In the 1770s and 1780s, he would return to
the puzzle and put other pieces into place. Priestley’s ‘experiments and
observations’ in 1778 caused him to refine his 1772 accounts of the restoration
of air. He wrote:
In general, the experiments of this year were unfavourable to my former
hypothesis. For whether I made the experiments with air injured by respiration,
the burning of candles, or any other phlogistic process, it [the air] did not grow
better but worse.
In most of the cases in which the plants failed to meliorate the air they were
either manifestly sickly, or at least did not grow and thrive, as they did most
remarkably in my first experiments in Leeds; the reason for which I cannot
(Priestley 1779–1786, Vol.I, p. 298, in Nash 1948, p. 359)
One of his problems was lack of sufficient light: experiments conducted
outdoors gave better results than those conducted indoors, especially indoors
away from windows. He scaled down the degree of conviction that he placed
in the restoring power of vegetation, saying:
Upon the whole, I still think it probable that the vegetation of healthy plants,
growing in situations natural to them, has a salutary effect on the air in which
they grow. For one clear instance of the melioration of air in these circumstances
should weigh against a hundred cases in which the air is made worse by it, both
on account of the many disadvantages under which all plants labour, in the
circumstances in which these experiments must be made, as well as the great
attention, and many precautions, that are requisite in conducting such a process.
I know no experiments that require so much care.
(Priestley 1779–1786, Vol.I, p. 299, in Nash 1948, p. 360)
Within a few months of penning the above letter, and while working on a
range of philosophical, theological and political tasks, he was prepared to
278 History and Philosophy: Joseph Priestley
think further about the source of the pure air he saw released by green matter
and plants in his phials. Initially, he thought it came from the green
matter or leaves, but he was able to devise a nice experimental test of
this hypothesis. In September 1779, he wrote to his good friend Benjamin
Franklin (1706–1790), relating that:
Though you are so much engaged in affairs of more consequence [drafting the
Declaration of American Independence], I know it will give you some pleasure to
be informed that I have been exceedingly successful in the prosecution of my
experiments since the publication of my last volume [his Experiments and
Observations on Different Kinds of Airs].
I have confirmed, explained, and extended my former observations on the
purification of the atmosphere by means of vegetation; having first discovered that
the green matter I treat of in my last volume is a vegetable substance, and then
that other plants that grow wholly in water have the same property, all of them
without exception imbibing impure air, and emitting it, as excrementitious to
them, in a dephlogisticated state.
(Schofield 1966, pp. 178–179)
Other experiments confirmed that the green matter, along with aquatic
green leaves, only produced pure air in the presence of sunlight; heat was no
substitute for light. Thus, the vegetable hypothesis was restored and, indeed,
extended: not only did vegetation restore atmospheric air depleted by fires
and animal respiration, it also restored water that had dissolved unhealthy
air and whose dissolved air was being rendered noxious by respiration of fish.
Priestley’s research on the restoration of air basically finished at this point.
Most of the outlines of what would, in the late nineteenth century, come to
be called ‘photosynthesis’ were in place.22
Priestley was aware of the need for control groups and for the identification
and control of variables in experiments, and of the need to be cautious in
deriving definite conclusions from experiments in natural philosophy. All of
this is inconsistent with the ‘narrow-minded dogmatist’ image of Priestley that
was so casually, and without foundation, broadcast by Thomas Kuhn – an
inconsistency that should not be lost on students and that might encourage
them to be careful about what they read in history, philosophy and education
texts and what they are told in lectures.
Features of Science
As with the pendulum example, the suggestion here is that philosophical
(methodological, ontological, metaphysical and epistemological) themes and
issues be identified and discussed at whatever level is appropriate to students
and their educational circumstance, when they are learning photosynthesis.
As will be argued in Chapter 11, teachers should be relaxed about just what
might constitute ‘the nature of science’ and think more about dealing with
History and Philosophy: Joseph Priestley 279
‘features of science’ in their classes, and doing this as they teach scientific
topics. Some of the features that clearly arise in a Priestley-informed, historical
approach to teaching photosynthesis are at least the following.
Metaphysics and Science
To the end of the sixteenth century, Aristotle was the most significant figure
in the history of Western thought. Along with everything else he accomplished,
he was the founder of biological science. He was an amazingly acute observer
of the natural world and wrote five books on animals and one on plants.23
However, for 2,000 years, two Aristotelian scientific/philosophical positions
– first, his account of plant nutrition; second, his account of the elemental
nature of air – thwarted the discovery and formulation of a correct account
of the ‘restoration of air’ (photosynthesis). Both Aristotelian positions grew
out of his more fundamental embrace of observation-based common sense as
the foundation of all natural philosophy. One contemporary Aristotelian
writes: ‘In an effort to understand nature, society and man, Aristotle began
where everyone should begin – with what he already knew in the light of his
ordinary, commonplace experience’ (Adler 1978, p. xi).
In his On Plants, Aristotle sees the parallel between plants and animals,
saying: ‘the absorption of food is in accordance with a natural principle, and
is common to both animals and plants . . . and animals and plants have to
be provided with food similar in kind to themselves’ (Barnes 1984, Vol.2,
p. 1253). In his treatise On the Soul, he mentions how plants are fed: ‘if we
are to distinguish and identify organs according to their functions, the roots
of plants are analogous to the head in animals’ (Barnes 1984, Vol.1, p. 662).
Plant roots and animal mouths both have the function of absorbing food.
Plants have their head, so to speak, in the ground; this accords with people’s
naive and immediate understanding, and with their agricultural practice:
plants build themselves up from seeds by taking food and water from the soil
through their roots. This was the basis of the medieval ‘analogist’ understanding of plants. Very slowly, this common-sense view of plants began to
be unravelled by seventeenth-century ‘experimentalist’ investigators who took
as their model, not Aristotelian observation of plants, but Baconian and
Galilean-like experiments on plants (Delaporte 1982).
The second conceptual barrier to an understanding of photosynthesis was
the Aristotelian conception of air. Until Priestley’s time, the understanding of
air as a single, fundamental, non-divisible element held sway in science (natural
philosophy) and, of course, in everyday life. In the Aristotelian worldview, or
scheme of things, water was another such singular element (along with earth
and fire). It was recognised that not all air was the same: just as water could
be made dirty and fouled, so too could air be contaminated by smoke, dust,
putrefaction and so on. Such was the bad air of mines, swamps, prisons, etc.
However, the bad airs were not thought of as a composite, they were regarded,
in modern terms, as a mixture; as with dirty water, the impurities were just
280 History and Philosophy: Joseph Priestley
added to, and carried in, the air and could be filtered out. The properties or
physics of air – in particular, air pressure and its dependence on altitude, and
the compressibility of air – had been investigated by Torricelli, Boyle, Pascal,
von Guericke and others, but not the composition of air. As has been
mentioned in Chapter 4, the Aristotelian ‘elemental’ category acted as an
‘epistemological obstacle’ to such investigations. Priestley well expressed this
understanding in his justly famous Experiments and Observations on Different
Kinds of Air:
There are, I believe, very few maxims in philosophy that have laid firmer hold
upon the mind, than that air, meaning atmospherical air (free from various foreign
matters, which were always supposed to be dissolved, and intermixed with it) is
a simple elementary substance, indestructible, and unalterable, at least as much
as water is supposed to be.
(Priestley 1775–1777, Vol.II, p. 30)
As will be further elaborated in Chapter 10, this Aristotelian and commonsense picture was beginning to break down in Priestley’s time. The mechanical
worldview of Galileo, Boyle, Newton and the new science was seen to render
pointless the whole Aristotelian metaphysical picture and its corresponding
scientific programme of explanations in terms of natures, forms and essences
transforming matter in accordance with inner teleological potentials. On the
Aristotelian account, an acorn seed contained the potential of the tree, and
this potential directed the development of the seed into an acorn tree, not a
banana tree or a rose bush. With the demise of Aristotelian metaphysics,
the idea of air and water as fundamental, homogenous elements was made
contingent or contestable: it was something that could be investigated by
empirical procedure, and this was done.
Experiment and Science
Along with the philosophical critiques of Aristotelian metaphysics, the new
science legitimated the experimental investigation of nature; it was no longer
constrained by the Aristotelian strictures on interfering with nature. For
Aristotle, natural philosophy was to study ‘natural motions’, not ‘violent
motions’; experiment, which constrained nature, resulted in unnatural motions
and, thus, shed no light on natural processes.24
Johann Baptista van Helmont (1577–1644), the Flemish physician and
cross-over figure between alchemy and chemistry, had published his famous
willow-tree experiment, showing that, over a 5-year period, a willow-tree
seedling planted in a pot gained around 164 lb of ‘tree material’, seemingly
just from the addition of water (Helmont 1648). Thus, water was apparently
being turned into wood, an earthy material; water was ‘transmuted’ into
earth, as the alchemists expressed it.
Robert Boyle (1627–1691), the well-known English natural philosopher and
less well-known alchemist, utilised van Helmont’s experiments in his detailed
History and Philosophy: Joseph Priestley 281
criticism of the Aristotelian metaphysical system published in his 1661 The
Sceptical Chymist. He bypassed Helmont’s potted earth by growing plants
just in water and found the same effect: the plant grew (an increase in earthy
material) just by addition of water. This result strengthened the alchemist’s
claim that water could be transmuted into earth, thus refuting the Aristotelian
view that they were separate elements. This was yet another case of scientific
practice forcing an adjustment in metaphysics.
Stephen Hales (1677–1761), the English clergyman, in his 1727 Vegetable
Staticks, recognised experimentally that air literally entered into plants when
they grew, and was in turn given off by growing plants. The worldview that
motivated and informed his quantitative and experimental investigation of
nature was the then standard Christian one:
Since . . . the all-wise Creator [had] observed the most exact proportions, of
number, weight and measure, in the make of all things; the most likely way,
therefore, to get any insight into the nature of those parts of the creation, which
come within our observation, must in all reason be to number, weigh and measure.
(Hales 1727, p. 1, in Scott 1970, p. 44)
Joseph Black (1728–1799), a Scottish chemist, had, by heating marble
(calcium carbonate), in 1756, isolated and identified carbon dioxide or ‘fixed
air’ as he called it.25 He recognised that it was a thoroughly different kind of
air from atmospheric air – it turned limewater milky and did not support
combustion. A colleague wrote of Black’s discovery that:
He had discovered that a cubic inch of marble consisted of about half its weight
of pure lime and as much air as would fill a vessel holding six wine gallons. . . .
What could be more singular than to find so subtile a substance as air existing in
the form of a hard stone, and its presence accompanied by such a change in the
properties of the stone.
(Leicester 1956/1971, p. 134).
Thus began the idea that there were a number of separate airs; the term ‘gas’,
coined by van Helmont, was not widely used. However, despite these
advances, the idea that common atmospheric air was a composite of airs
(gases) was not at all widespread. As late as 1771, the French chemist Turgot
was writing of air as a ‘ponderable substance which constantly enters into the
state of vapour or expansive fluid according to the degree of heat contained’
(Brock 1992, p. 102).
Worldviews and Science
The educational importance of connecting science and worldviews was
recognised by the AAAS in its Project 2061: ‘Becoming aware of the impact
of scientific and technological developments on human beliefs and feelings
282 History and Philosophy: Joseph Priestley
should be part of everyone’s science education’ (AAAS 1989, p. 173). A
historical approach to teaching photosynthesis allows context for discussion
and elaboration of these abstract themes.
Pringle’s much-cited Copley Medal address well conveys the overarching
sense of cosmic design, teleology and anthropocentric purpose that constituted
Priestley’s worldview and that of most natural philosophy of the period.
The ideas of design and providence were famously articulated by another
of Priestley’s contemporaries, William Paley (1743–1805), whose Natural
Theology (Paley 1802/2006) was a compulsory text for all students in
Cambridge and Oxford. It was the deep-seated idea of providence that, for
most, flowed naturally from belief in a beneficent Creator. God was absolutely
pervasive in medieval and early-modern natural philosophy; for all natural
philosophers, nature was in the foreground of their investigations, but God
was the background; they simply assumed that they were studying God’s
handiwork, in much the same way as a person today studying a clock is aware
that they are studying something that someone made, and that what they are
seeing reflects good or bad design and craft skills.26
Providence was variously held to be operative at three levels: it governed
the natural world (the occurrence of earthquakes, storms, etc.), it controlled
human history (the outcome of wars, etc.), and finally it was operative in
individual human lives (recovery from illness, avoidance of accidents, etc.).
For Muslims, ‘God willing . . .’ still prefaces all claims about future events.
Priestley shared this ubiquitous worldview. In his First Principles of Govern –
ment, he wrote:
Such is my belief in the doctrine of an over-ruling providence, that I have no doubt,
but that every thing in the whole system of nature, how noxious soever it may
be in some respects, has real, though unknown uses; and also that every thing,
even the grossest abuses in the civil or ecclesiastical constitutions of particular
states, is subservient to the wise and gracious designs of him, who, notwithstanding
these appearances, still rules in the kingdoms of men.
(Miller 1993, p. 6)
Priestley’s investigation of the restoration of air cemented his worldview.
For him, nature is shown thus to be so wonderfully formed that ‘good never
fails to arise out of all evils to which, in consequence of general laws, most
beneficial to the whole, it is necessarily subject’ (Priestley 1774–1786, Vol. II,
p. 63). In his Memoirs, he wrote that the greatest virtue of scientific studies
was their tendency ‘in an eminent degree, to promote a spirit of piety, by
exciting our admiration of the wonderful order of the Divine Works and
Divine Providence’ (Priestley 1806/1970, p. 200). And further, with the
philosophical unbelievers of the Enlightenment directly in mind (just as Isaac
Newton had in writing the Principia), Priestley adds that those of a ‘speculative
turn’ could not avoid the perception and admiration of ‘this most wonderful
and excellent provision’ (ibid.).
History and Philosophy: Joseph Priestley 283
The significant issue in discussion of science and worldviews is just how,
and if, any particular worldview is supported, or contradicted, by science.
Abductive Reasoning
Priestley’s argument for a providential worldview is best understood as neither
a deductive argument (which would clearly be invalid) nor as an inductive
inference (the argument is not from a sample to a whole), but as an abductive
argument, to use the term introduced by Charles Sanders Peirce in the late
nineteenth century (Aliseda 2006). More recently, this kind of argument has
been called ‘inference to the best explanation’ (Lipton 1991, Psillos 2004)).
Its structure is:
There is some well-documented observation O about the world.
If some theory or supposition T were true, then O would be expected to be the
Therefore O provides grounds for believing in the truth of T.
Priestley’s final step from the understanding of natural processes to knowledge of divine (supernatural) properties, from knowledge of the world to
knowledge of God, was the standard inference in all natural theology
(theological speculation that was independent of revelation). In the eighteenth
century, it was a step taken by nearly all natural philosophers.
In his History of Electricity, Priestley had written:
The investigation of the powers of nature, like the study of Natural History, is
perpetually suggesting to us views of the divine perfections and providence, which
are both pleasing to the imagination, and improving to the heart.
(Priestley 1767/1775, p. iv)
Priestley realised that this step was not logically compelling, it was not
demonstrative. It was ‘suggestive’, but psychologically it ‘could not be avoided’.
In the eighteenth century, both things were true, given background knowledge
and culture; but then, and now, the step was not logically compelling; it was
not demonstrative. Priestley well knew that the step from observation of
nature to unseen natural mechanisms did not result in indubitable knowledge.
Aristotle and the medievals recognised the same limitation for this argument
form; they knew that an argument of the following form is invalid:
T (theory) implies O (observation)
O (observation occurs)
Therefore T (is true)
The argument commits the Fallacy of Affirming the Consequent (also known
as modus ponens): many other Ts could also imply O, and, thus, any particular
284 History and Philosophy: Joseph Priestley
T was not proved by occurrence of O. Consequently, the step from observation
to supernatural mechanisms was even less compelling.
‘Argument to the best explanation’ can be illustrated using one of Peirce’s
examples: if we find fish fossils inland, far from the current ocean shore (O),
then we can abduce the theory or hypothesis that the ocean once covered the
area (T). This theory provides the best current explanation of O. Thus, O
provides support for belief in T. This typical piece of scientific reasoning is
neither deductive nor inductive; Peirce labelled it ‘abductive’ and, of course,
he recognised that it was not demonstrative (Peirce 1931–1935, Vol.2,
p. 629). The observation O provides support for belief in T; it does not prove
the truth of T. The process begins with the scientific assumption that there
has to be some explanation of O; in science, there is also the assumption
that there is a natural explanation of O; super-natural best explanations are
not allowed, as will be elaborated in Chapter 10; they are ruled out by
commitment to methodological naturalism.
For Priestley, O was the restoration of air, and T was his Christian worldview. The latter provided the best explanation of the observed phenomena.
He knew that inferences to the best explanation were still tentative and not
demonstrative. However, the inference had another support: Priestley was
an ardent believer in the Christian Revelation; his entire life was spent as a
Christian clergyman and serious scholar of scripture. His view was that the
two classes of premise – observations of nature plus revelation correctly
interpreted – jointly justified a compelling inference to divine or supernatural
agency as the best explanation of the observations and effects his science
However, within half a century of Priestley’s death, the work of Darwin
would severely challenge, and for many completely undermine, the theistic
picture of a providential natural world. This was, at least, the case for the
natural level of providential operation, Darwinism having nothing to say
about either historical or personal levels. Priestley’s observations about natural
processes, such as the role of vegetation in the restoration of air, would hold,
but less and less was there agreement with his theological explanations of the
observations. After Darwin, the recognition of adaptation without design was
a commonplace; there was a competing ‘best explanation’ for the existence
of O that was also a natural explanation; it did not require recourse to
supernatural agency. Many gave up Judaeo-Christian (and Islamic) belief;
many retained the belief sans providence; many, such as contemporary
‘Intelligent Design’ proponents, reinterpreted providence to align it with a
seemingly ‘independently functioning’ world.27
Priestley provides ample opportunity for the elaboration and appraisal of a
long-standing ontological position in philosophy, namely materialism. Priestley
believed in a single God above and a single matter below. He was a materialist:
History and Philosophy: Joseph Priestley 285
his ontology did not allow spirits, souls or minds of a kind that were
ontologically distinct from matter.28 He was an ontological monist, writing:
What peculiar excellence is there in those particles of matter which compose my
body, more than those which compose the table on which I write. . . . If I knew
that they were instantly, and without any painful sensation to myself, to change
places, I do not think it would give me any concern.
(Gibbs 1967, p. 99)
In the Introduction to his edition of Hartley’s Theory of the Human Mind,
Priestley writes:
I rather think that the whole man is of some uniform composition, and that the
property of perception, as well as the other powers that are termed mental, is the
result (whether necessary or not) of such an organical structure as that of the brain.
(Priestley 1775, p. xx)
Although seemingly a contradiction, his was a Christian materialism, as clearly
stated when he reflected upon the impact of his writings:
The consequence (which I now enjoy) is a great increase of materialists; not of
atheistical ones, as some will still represent it, but of the most serious, the most
rational and consistent christians.
(Passmore 1965, p. 169)
Priestley rejected any belief in the soul as existing apart from the body; this
was a ‘false philosophy from the East’ and was entirely without scriptural
warrant. He regarded belief in an independent and individual soul, and its
required ontology that separated matter and spirit, as entirely un-Hebraic,
un-Christian and the root of most aberrations, fantasies and corruptions in
the Christian churches. In 1778, he wrote to the Revd C. Rotherham that:
I was an Arian till I went to Leeds, and my Materialism is but of late standing,
though you see that I now consider the doctrine of the soul to have been imported
into Christianity, and to be the foundation of the capital corruptions of our
(Priestley 1806/1970, p. 40)
For Priestley, not only was belief in a soul un-Christian, it was just
philosophical folly. One had to embrace some version of either Platonism or
Aristotelianism for the soul to make philosophical sense, and he rejected both.
Ethics and Animal Experimentation
Until Priestley’s new nitrous air test, the only means available for ascertaining
the ‘goodness of air’ were variants of the miner’s canary test; most commonly,
286 History and Philosophy: Joseph Priestley
a laboratory mouse was placed in a sealed container of the air to be tested,
and its ‘goodness’ was measured by how long the mouse lived. The mouse
test stoked the embryonic Romantic and humanistic reactions against the new
science, which were so dramatically captured by Joseph Wright of Derby in
his evocative 1768 painting of An Experiment on a Bird in the Air Pump.
There, a bird lies dead from suffocation in an evacuated jar, with a pensive
audience looking on, and one woman looking away, inviting a ‘science is not
for women’ response in viewers.
Priestley encountered this reaction: Anna Laetitia Aikin, the daughter of
a close friend and an admirer of Priestley, published a book of verse in 1773
that contains a poem entitled ‘The Mouse’s Petition’ – it concerns a mouse
that she found in a cage in Priestley’s study. She knew the nature of his
experiments and also of his championing of human freedom, and so she wrote
the piece, leaving it alongside the mouse cage to provoke him.29
O hear a pensive prisoner’s prayer,
For liberty that sighs;
And never let thine heart be shut
Against the wretch’s cries!
For here forlorn and sad I sit,
Within the wiry grate;
And tremble at the approaching morn,
Which brings impending fate.
If e’er thy breast with freedom glowed,
And spurned a tyrant’s chain,
Let not thou strong oppressive force
A free-born mouse detain!
Pleasingly for countless generations of mice, for the repute of science and for
precision in pneumatic measurement, Priestley was so moved by the poem that
he found a new chemical test for the goodness of air.
As has been discussed in Chapter 5, questions of values, ethics, morals and
science cannot be avoided in science programmes. All major universities now
have ethics committees that regulate research in science and social science that
impinges directly and indirectly on humans, animals and, more broadly, social
welfare, and researchers need to justify their methods and aims to such
committees. The once straightforward and unreflective use of animals for
scientific experiments and laboratory dissections is now strictly controlled
(Rollin 2009). More than this, however, concern for animals is explicitly
cultivated and even demanded – an aim of the New Zealand science syllabus
is ‘the care of animals’ and recognition of their rights. Hitherto, partly under
the influence of belief in value-free science, these questions have largely been
ignored in science education – rats, mice and frogs were routinely killed in
History and Philosophy: Joseph Priestley 287
furtherance of curricular objectives. The Priestley example allows this
philosophical and educational subject to be placed in historic context and
provides an occasion for students to analyse and debate the issues.
Commercialisation of Science
In 1767, Priestley became first person to create and bottle soda water, or
‘Pyrmont water’ as he called it.30 Pyrmont was a famous medicinal spa in
Hanover. Priestley saw that the Pyrmont bubbles were carbon dioxide (fixed
air), which he had captured as a by-product of a Leeds brewery and which
he was able to independently produce by mixing chalk and acid and capturing
the emitted air in a bladder, thus putting it under pressure. There was, at the
time, great interest in ascertaining the efficacious component of English and
Continental mineral waters, but no one was thinking of manufacturing them.
Priestley, who recognised the enormous wealth that could be made,
nevertheless turned down the opportunity of commercial bottling of his
Pyrmont water, saying that natural philosophers should ‘search for truth, not
money’. The commercial opportunities were not lost on Johann J. Schweppe
(1740–1821), who, from 1793, began manufacturing and selling high-pressure
soda water from his factory off Cavendish Square. As they say, the rest is
Priestley’s innocent, almost saint-like, turning away from the commercial
windfall that would have followed his selling his revolutionary soda-water
process can be an occasion for taking up the whole issue of science’s
engagement, if not entanglement, with business and commerce. This is not as
simple as Romanticists might wish: Priestley was a champion of applied
science and the commercial utilisation of scientific knowledge; for him,
pursuing good science was both a religious obligation and the way of
furthering the Enlightenment project of ‘improving man’s estate’; hence, his
support of the manufacturing and business-focused Lunar Society (Schofield
1963, Uglow 2002). The commercialisation of science and its implications for
‘the nature of science’ have been much written on over the past few decades.32
Has science ‘sold its soul’ or ‘gained a body’? If NOS curricular objectives
are extended beyond the usual methodological and epistemological core, then
commercialisation warrants the attention of teachers and students.
Priestley in the Classroom
William Brock, in his massive The Fontana History of Chemistry, describes
Priestley as ‘one of the most engaging figures in the history of science’ (Brock
1992, p. 99). Enough has been indicated here to give credence to Brock’s claim.
Enough has also been said to support the claim that the practice of science is
interwoven with philosophy and worldviews; all three mutually affect each
other. As mentioned at the outset of the chapter, there are three strong
considerations that make easy the utilisation of Priestley’s life and work in
classrooms: the acknowledged environmental problem of the ‘goodness of air’,
288 History and Philosophy: Joseph Priestley
the inclusion of ‘nature of science’ in many curricula, and the widespread
concern with reappraising aspects of the European Enlightenment tradition.
With informed teachers, Priestley can be used to further student understanding
of each of these matters.
With the lessons from the past few decades of incorporating historical and
philosophical studies into science programmes,33 there are some obvious ways
in which Priestley’s work might be incorporated.
Historical Vignettes
Suitable for the curriculum at any level is the presentation by students or
teachers of brief historical vignettes concerning Priestley. At a minimal level,
this is designed to put a human face on chemistry and biology lessons and to
indicate something of the history of the subject. Such vignettes can be tailored
to the interests, sophistication and grade level of the class. Topics might
include Priestley’s religion, his politics, his educational theory and practice,
his marriage and family life, his support of the American and French
Revolutions, his dealings with Lavoisier, his creation of soda water, his
opposition to the new oxygen theory of combustion, his opposition to
colonisation and the slave trade, his influence on the Founding Fathers of the
US and so on.
Additionally, vignettes might be presented on the wider scientific, political,
social, religious and intellectual circumstances of Priestley’s time: the practice
of religious discrimination; the intertwining of religion and state in Europe
and England; the role of science in the French and English Enlightenments
and its role in European Imperialism; the state of parliamentary government;
European colonisation; the impact of the French Revolution; the social effects
of embryonic capitalist production in England; the role of science in the
furtherance of navigation, commerce and industry. Vignettes can take the form
of individual or group essays that might be presented to the class as talks or
powerpoint presentations. They can contribute to better understanding of
scientific content; to better appreciation of the scientific tradition and,
hopefully, a sense of being indebted to that tradition; to increased interest in
science; and to more general educational goals concerning students’ sense of
place, culture and identity. One not inconsiderable advantage of vignettes is
that they allow controversial matters to be dealt with in classrooms with the
safety of historic remove. Whereas, for example, critical discussion of the state,
of censorship and of religious entanglement in the state might be dangerous
or forbidden in many contemporary Western and Islamic societies, or in
Communist China, it can be relatively safe and objective to discuss these
matters in the context of Priestley’s life, times and arguments.34
Historical–Investigative Teaching
A more rigorous way of bringing Priestley to the classroom is to try to wed
laboratory classes to historical stories; that is, to follow along the path of
History and Philosophy: Joseph Priestley 289
experimental science; to follow in the footsteps of the masters, as one might
say. While doing this, it is possible to reproduce something of the intellectual
puzzles and scientific debates that originally prompted the experiments.
Participation in this sort of journey can give students a much richer appreciation of the achievements, techniques and intellectual structure of science,
while developing their own scientific knowledge and competence.
Ernst Mach (1838–1916) recognised this at the end of the nineteenth
century, when he wrote:
Every young student could come into living contact with and pursue to their
ultimate logical consequences merely a few mathematical or scientific discoveries.
Such selections would be mainly and naturally associated with selections from
the great scientific classics. A few powerful and lucid ideas could thus be made
to take root in the mind and receive thorough elaboration.
(Mach 1886/1986, p. 368)
With the exception of Westaway, Holmyard, Bradley and a few others in
England, and Conant and some others in the US, Mach’s suggestions were
ignored by science teachers. Mach’s approach was famously taken in Conant’s
Harvard Case Studies in Experimental Science (Conant 1948). Chapter 2 is
titled, ‘The Overthrow of the Phlogiston Theory: The Chemical Revolution
of 1775–1789’ (Conant 1948), and Chapter 5 is titled ‘Plants and the
Atmosphere’ (Nash 1948). The chapters provide historical texts, glossaries,
details of experimental apparatus and so on, all of which can be utilised in
classroom discussion of Priestley.
In recent times Nahum Kipnis has promoted this historical–investigative
approach (Kipnis 1996). He has, for example, based a course on optics around
retracing the classic, and usually very simple, experiments and demonstrations
in the history of the subject (Kipnis 1992). Students read original literature,
they re-enact historical experiments and themselves elaborate and debate
interpretations of what they see in the laboratory. Readings and experiments
on photosynthesis could suitably be substituted for the optics material. In such
courses, students do not just read history, they do practical work and carry
out investigations, but, instead of the practical activities being isolated, they
are connected with a tradition of scientific development.35
Another current example of this historical–investigative approach is at the
University of Chester, where John Cartwright has taught an elective history
of science course that has a 4–6-week component on The Discovery of
Oxygen. The course aims are:
1 to promote an understanding of the historical origins of science and the
distinctive nature of scientific enquiry;
2 to develop an awareness of the interaction between scientific thinking and
the wider culture;
3 to foster an empathetic understanding of ideas from previous cultures;
4 to develop an awareness of the nature of historical enquiry;
290 History and Philosophy: Joseph Priestley
5 to enable students to appreciate the force and impact of scientific thinking
and ideas.
The course and its Student Guide (Cartwright 2004) are a nice example
of a wider, contextual approach to the teaching and learning of chemistry.
It could provide a template for a comparable course on The Discovery of
Priestley’s studies on the restoration of air are well suited to this historical–
investigative approach. A good many of his discoveries are relatively simple
to reproduce: making soda water, producing oxygen by heating metal oxides,
darkness versus light conditions for effectiveness of green plants in restoring
air, the nitrous air test, the observation of ‘green matter’ and the conditions
under which it creates pure air and so on.
What makes the use of Priestley attractive is that he wrote very complete
and readable accounts of his work. Priestley meant for his experiments to be
reproduced by readers. His writings were a means for the education of the
populous and, thus, to realising Priestley’s conception of the true goal of the
Enlightenment – the development of an informed citizenry who respected
reason, were distrustful of authority, prized autonomy and recognised an
open society and public debate as the preconditions of knowledge growth in
all fields of endeavour, but especially for scientific and religious understanding.
Priestley was an advocate of ‘science for all’, some two centuries before it
became an educational slogan.
Interdisciplinary Teaching
Priestley’s intellectual engagements were wide-ranging – science, theology,
education, politics, history, philosophy – it is unrealistic to think that all this
can be covered in a science course. However, it is not unrealistic to hope that
some coordination between subject areas can be achieved in a school, or
college, and, thus, for teachers in related fields to work together on the ‘big
picture’ presented by Priestley’s work.
Such coordination is, of course, almost unheard of in school systems.
History, science, mathematics, music, social studies, literature, religion and
philosophy – all go their own way, with barely a passing curricular nod to
each other. From the students’ point of view, and even from the teachers’,
knowledge is truly fragmented. However, well-chosen themes, such as ‘the
restoration of air’, that are heuristically rich, can organise a curriculum to
maximise the degree to which the interdependence of knowledge becomes
more transparent. It may be, minimally, a matter of looking at existing,
independently generated curricula and simply pulling the related parts together
and arranging for some coordination and cross-referencing, but it can be
more than this.
A praiseworthy example, and potential model, of coordination between
disciplines occurs at the Oberstufen Kolleg of the University of Bielefeld,
History and Philosophy: Joseph Priestley 291
Germany. The college utilises a ‘historical–genetical approach to science
teaching’. At the Oberstufen Kolleg:
There is attention given to the historical, social and philosophical dimension of
science. Frequently, historical examples are presented in a rather anecdotal fashion
in courses of science, in order to motivate students for the ‘real thing’, the scientific
content. History and philosophy are merely instrumentalised and serve to ‘sell the
product’. Our intention differs: we consider the historical and philosophical
dimension to be an essential part of science and of instruction in science, that
aims to present science in a social and historical context.
(Misgeld et al. 2000)
Further examples of such cross-disciplinary and coordinated teaching are
the various science, technology, engineering, arts and mathematics (STEAM)
curricula in the US, Korea and some other countries,36 and some such efforts
towards coordination are part of the US Next Generation Science Standards
statements, where ‘cross-cutting’ concepts and curricula are identified and
Reading, understanding in their context and appreciating selections from
the range of Priestley’s work on restoration of air, on methodology, on
philosophy and theology, along with some historical–investigative redoing of
his simple experiments, would make excellent material for such cooperative,
interdisciplinary curricula. The school curriculum might then look something
like the following table (Figure 7.1) with subjects or disciplines in the columns
and topics in the rows.
Priestley is an under-utilised figure in science education. Although his
contribution to the discovery of oxygen is recognised, this is usually glossed
by comment about him being an obscurantist concerning Lavoisier’s new
chemistry and a dogmatist concerning his own adherence to the phlogiston
account of combustion and respiration. Unfortunately, Priestley’s contribution
to the modern understanding of photosynthesis is seldom mentioned in school
curricula. This is a pity, as his role was pivotal, and students can very easily
be led through many of the same steps that he took. There is the opportunity
for students to ‘walk in the footsteps’ of a great scientist and, thereby, not
only learn scientific content, method and methodology, but also get a sense
of participation in a tradition of thought and analysis that is at the core of
the modern world.
Such Priestley-guided participation allows students to appreciate and
understand key elements of the scientific tradition: hard work, experimentation, independence of mind, a respect for evidence, a preparedness to bring
scientific modes of thought to the analysis and understanding of more general
social and cultural problems, a deep suspicion of authoritarianism and
292 History and Philosophy: Joseph Priestley
dogmatism, and the concern for promotion of an open society as the condition
for the advance of knowledge.
Bringing Priestley into education allows light to be shed upon the mutual
interaction of worldviews and science; it allows the scientific sources of the
European Enlightenment to be investigated; and it allows the evaluation of
the special Enlightenment niche occupied by Priestley, namely the theistic,
albeit dissenting, strand of the Enlightenment. Understanding and appreciating
this connection between science and the Enlightenment and having the
opportunity to examine what is dead and what is living in that tradition can
be a major contribution of science classes to the general education of students
in the modern world.
1 This chapter is dependent on research published in Matthews (2009).
2 Among countless studies documenting children’s inadequate (given age and grade level)
understanding of photosynthesis see: Cañal (1999), Eisen and Stavy (1988), Wandersee
(1985) and references therein.
3 The term ‘photosynthesis’ was coined in 1898 by the Englishman Charles Barnes
(1858–1910) to denote the complex biological–chemical process of the ‘synthesis of
complex carbon compounds out of carbonic acid, in the presence of chlorophyll, under
the influence of light’ (Gest 2002, p. 7).
The equation for the process is:
6CO2 + 6H2O + solar energy → C6H12O6 + 6O2
History and Philosophy: Joseph Priestley 293
Religion History Science Philosophy Technology
Figure 7.1 HPS-Informed Curricular Linkage. (a) Revelation, (b) French Revolution, (c)
composition of air, (d) experiment, (e) soda water, (f) epistemology, (g) the
Enlightenment, (h) providence
4 For details, see Chapter 2 and the references therein.
5 The definitive and exhaustive biographical study of Priestley is Robert Schofield’s twovolume work (Schofield 1997, 2004). See also the studies of William Brock (Brock 2008)
and John McEvoy (McEvoy 1978–79, 1990, McEvoy & McGuire 1975) and
contributions to Rivers and Wykes (2008) and Anderson and Lawrence (1987).
6 In his Memoirs, Priestley writes: ‘I felt occasionally such distress of mind as it is not
in my power to describe, and which I still look back upon with horror’ (Priestley
1806/1970, p. 71).
7 For accounts of the dissenting academies, see Wykes (1996).
8 Richard Westfall, in his biography of Newton, says that Cambridge at the time was
‘fast approaching the status of an intellectual wasteland’ (Westfall 1980, p. 190).
9 A good popular account of the intellectual entanglement of Priestley and Lavoisier is
Jackson’s A World on Fire (Jackson 2005).
10 For a selection of Priestley’s political writings, see Miller (1993).
11 For studies of Priestley in America, see Graham (2008).
12 Priestley’s house in the town long functioned as the Priestley Museum and Research
Centre. Sadly, state budget cuts have now closed it.
13 There are numerous studies of Priestley’s theological and religious life; see especially
Brooke (1990) and Wykes (2008).
14 A full bibliographic listing of Priestley’s books, pamphlets and articles is contained in
Schofield (2004, pp. 407–422).
15 See references in Chapter 2.
16 At the time, ‘moral philosophy’ covered a broad field; it meant more or less all studies
other than ‘natural philosophy’ (or science, in our terms).
17 For Priestley’s materialism, see Priestley (1778). For critical exposition and discussion
of his position, see Schofield (1970, pp. 261ff.) and Dybikowski (2008).
18 Modern teachers trying to dissuade students of their ‘fluid’ view of electricity are
following in Priestley’s footsteps.
19 This was a 12-inch (30-cm) magnifying glass, with a 20-inch (50-cm) focal distance,
that gave more heat than any other means available. Continental chemists were
purportedly using it to melt diamonds.
20 All Royal Society Transactions papers are now available on the Society’s web page.
21 For further details of the paper and the Copley Medal, see Guerlac (1957) and McKie
22 After the passage of 60 years, a still excellent treatment of the historical development
of early photosynthesis studies is the essay of Leonard Nash in James Conant’s Harvard
Case Studies in Experimental Science (Nash 1948, pp. 369–434). For more recent
work, see Magiels (2010).
23 See the excellent, two-volume Jonathan Barnes edition of Aristotle’s Collected Works
(Barnes 1984).
24 For qualification of this standard interpretation of Aristotle, see Newman (2004,
Chapter 5).
25 Called ‘fixed’ because he thought it was, as a whole air, trapped or ‘fixed’ in calcium
and other metal carbonates; the heating released the air; when dissolved in limewater
and precipitated, it again became fixed.
26 For informed discussion of providence and science, see at least: Funkenstein (1986) and
contributions to Lindberg and Numbers (1986).
27 These are all philosophically and theologically complex options. Clearly, Christian and
Islamic belief among philosophically and scientifically sophisticated people survived
Darwin, with many retaining some conception of providence.
28 On Priestley’s materialism, see Schwartz (1990) and Yolton (1983, Chapter 6).
29 The poem is in O’Brien (1989, p. 62). This book also contains a wealth of material on
Warrington Academy and Priestley’s teaching career there.
30 See Priestley (1772a). An informative discussion of the soda-water episode, with
diagrams of apparatus, can be found in Gibbs (1967, pp. 57–58, 69–70). See also Coley
(1984) and Golinski (1999, pp. 112–117).
294 History and Philosophy: Joseph Priestley
31 This explains why ‘1793’ is stamped on the tops of Schweppe’s drink bottles.
32 See at least: Kitcher (2001), Resnik (2007) and contributions to Irzik (2013) and to
Radder (2010).
33 See contributions to the journal Science & Education from its first volume in 1992 to
the present.
34 See Wandersee and Roach (1998) for examples of types and effectiveness of such
35 For an extensive overview and appraisal of this ‘historical–investigative’ tradition, see
Heering and Höttecke (2014).
36 These are coordinated and integrated coordinated science, technology, engineering, art
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