Updated 1 Feb 2005

WIRKSWORTH Parish Records 1600-1900

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Rev. Abraham Bennet, an Appreciation

This appreciation of Abraham Bennet, (1749-1799), Curate of Wirksworth and Fellow of the Royal Society, was written by Paul Elliott and published by Online journals of The Royal Society. Copyright lies with the Author and The Society. The Royal Society has granted permission for use of this material.
Paul Elliott writes: I am now at Nottingham University and I was wondering if you would mind putting that down if anyone does want to contact me regarding Bennet. My Email is Paul.Elliott@Nottingham.ac.uk. My current address is: Dr. Paul Elliott, School of Geography, University of Nottingham NG7 2RD


    Reference: Paper by P Elliott, Abraham Bennet,FRS(1749-1799): A provincial Electrician in Eighteenth Century England, from Not. Rec. Roy. Soc. Lond. Vol 53, No 1, pp 59-78 (1999)


    ABRAHAM BENNET, F.R.S. (1749-1799): A PROVINCIAL ELECTRICIAN
    IN EIGHTEENTH-CENTURY ENGLAND

    by
    PAUL ELLIOTT
    172 Clarendon Park Road, Leicester LE2 3AF, UK

    SUMMARY
           Abraham Bennet was a clergyman and electrical experimenter who invented the gold-leaf electroscope and the doubler of electricity. He used a mechanical revolving version of the latter to devise a concept of 'adhesive electricity', which had an important influence on Volta in the formulation of his contact theory of electromotivity. Bennet managed to balance his clerical position, obtained by patronage, with the friendship and assistance of the local philosophical community, which included Erasmus Darwin, White Watson and the members of the Lunar and Derby Philosophical Societies. The Lunar members helped him to publish his research and supported his nomination as F.R.S. in 1789; however, the relative harmony of the philosophical community represented by the Royal Society, which temporarily united provinces and metropolis, was shattered by the political turbulence of the revolutionary era. The delicate balancing act that allowed Bennet to claim support from Banks and Kaye at the same time as from Priestley and Darwin became more difficult and Bennet’s research activity foundered due to ill health and political division.

    INTRODUCTION
           Announcing the discovery of the pile in 1800, Alessandro Volta (1745-1827) paid tribute to three British electricians who had stimulated his work; these were William Nicholson (1753-1815), Tiberius Cavallo (1749-1809) and Abraham Bennet.1 Bennet remains by far the least known of the three despite the fact that contemporaries including Davy and Erasmus Darwin recognized his importance. This neglect has been due in part to the fact that Bennet was based in the small Derbyshire town of Wirksworth. Yet in the later 18th and early 19th centuries, there was a vibrant scientific culture in the English provinces exemplified by the Lunar Society of Birmingham and the Manchester and Derby Philosophical Societies. Bennet had connections with both the Derby Society and the Lunar Society. Provincialism did not mean parochialism or irrelevance and a reappraisal of Bennet’s position in the history of science is long overdue.

    ABRAHAM BENNET, CURATE OF WIRKSWORTH
           Born in 1749, the son of Abraham Bennet, schoolmaster of Whaley Lane, Cheshire, and his wife, Ann Fallowes of Cheadle, Abraham Bennet was baptised at Taxal, Derbyshire, on 20 December. He was probably the eldest son, but had at least one brother, named William. 2 Abraham married and his widow, Jane, was to survive him for 27 years, dying at Mappleton in July 1826. 3 They had six daughters and two sons. In September 1775, he was ordained in London and appointed to curacies at Tideswell and a year later at Wirksworth, on a double stipend of £60 per annum.4 A memorial tablet in Wirksworth church records that he was additionally, ‘Rector of Fenny Bentley; Domestic Chaplain to his grace the Duke of Devonshire; Perpetual Curate of Woburn and Librarian to his grace the Duke of Bedford.’ He was the author of New Experiments on Electricity (1789) which ‘established his reputation for science amongst the philosophers of all countries’. Bennet’s name is recorded in the list of schoolmasters at Wirksworth Grammar School, where he is described as M.A.5 His notebook has survived and a portrait of him hangs in the vestry of Wirksworth Church which is half-length, done in oils and about 10.5 by 9 inches in size (figure 1). The picture, though in need of a clean, clearly shows a profiled figure in clerical dress with grey hair, a large forehead and a straight, aquiline nose. It can be dated to between 1789 and 1799 because Bennet is shown holding a copy of his New Experiments with another book and a roll of parchment, probably representing his scientific papers. In

    Figure 1. Portrait of Abraham Bennet by an unknown artist kept in the vestry of St Mary’s Church, Wirksworth, showing him with copies of his works. Reproduced from Ann. Sci. 1, plate v, pp. 98–99 (1936), with the kind permission of Taylor & Francis. [see also X253 for a better photo of the painting of Bennet]

    addition to his own speculations, Bennet’s notebook contains extracts from books, periodicals and newspapers demonstrating the thought processes of a man of the 18th century ‘well versed in different branches of natural philosophy’. 6 Bennet died in 1799 after a ‘severe illness’ and was buried on 9 May.7

    THE NEW EXPERIMENTS ON ELECTRICITY
           The New Experiments was published by subscription and contained a summary of all his electrical work to date. Of most importance are his invention of the gold-leaf electroscope, invention of the doubler of electricity and anticipation of Volta’s contact theory.8 In the New Experiments, Bennet described his general electrical theory and the new electroscope before giving an account of experiments with a Lichtenberg electrophorus with reproductions of chalk figures and patterns that he produced. The phenomenon of electricity caused by evaporation—for example from heated metals plunged into water— was illustrated, followed by a description of the doubler. The work concluded with a theory of atmospheric electricity and how different electrical states were associated with different weather conditions, but the most important sections described the mechanization of the doubling process and the experiments on ‘adhesive electricity’.

           Various phenomena had always betrayed the existence of electric charge produced in different ways, such as rubbing wool on glass. Threads and pieces of leaf brass had been used in the early 18th century because they would diverge if electrified. The first real electrometer was invented by John Canton (1718-1772) and used a pair of pith balls hung on fine linen threads. On the air being electrified in a room, the balls would diverge. The invention of the Leyden jar showed that electricity could be ‘stored’ and perhaps the strength of the charge estimated. The jar consisted of a bottle partly filled with water that contained a metal rod projecting through the neck. Foil was placed inside and outside the bottle to prevent damage to the leaves. If the rod was connected to the prime conductor of a static generating machine and then the jar taken away, it was found that the charge could be kept and transported.9

           Electrical theories followed the suggestions in the queries of Newton’s Optics (1723), which had speculated about the properties of the mysterious ether apparently inhabiting the universe and seeming to obey the laws of attraction and repulsion. The electrical theory of Benjamin Franklin (1706-1790) which became widely known after 1750—primarily in connection with experiments culminating in the invention of the lightning conductor—was no exception. According to the Franklin’s theory, largely accepted by Bennet, there were three states of electric charge, positive, negative and the state of equilibrium. In the positive state, charged bodies held an abundance of the electrical ‘fluid’ and in the negative state, there was a privation or lack of fluid. The state of equilibrium was the natural state of charge of a body. The Franklinist system suffered from one obvious problem, how to explain the fact that negatively charged bodies repulsed each other. One answer was a rival theory which held that there were actually two electrical fluids, the vitreous (positive) and the resinous (negative) fluid, thus, the charging of a body by rubbing would represent the rushing of one kind of ‘fluid’ into the place previously occupied by the other. The two theories were incommensurable, as no experiments had been devised which could conclusively prove either.10

           Bennet’s electroscope was based on another instrument made by his friend Cavallo. Instead of threads or pith balls, Cavallo used silver wire terminated by pieces of cork contained in a glass bottle and held in place by a glass tube. A wire ran from the tube to the large brass cap and strips of tin-foil (earthed) allowed the electricity to be ‘conveyed off’ when the corks touched. Many of these innovations were adopted by Bennet, but his electroscope was larger with a 5-inch tall glass case (figure 2).

    Figure 2. Bennet’s gold-leaf electroscope and simple doubler.

    Two inches in diameter, it rested on a wood or metal base. Two slips of leaf-gold were suspended in the glass, and the peg and tube holding them touched the outer cap. Two pieces of tin foil were fastened on opposite sides of the internal surface of the glass.11 Bennet’s electroscope was important because the glass case allowed atmospheric electricity to be easily detected without interference from air currents. The instrument was more sensitive than other kinds because it was larger and because the gold leaves were finer and lighter than other materials. Bennet put the electroscope to use in a series of experiments detecting the presence of charge, such as when different types of powder were blown at the electrometer and found to register electricity. He compiled a diary of the charge present in different weather conditions. To carry out some of these tests he utilized an extraordinary apparatus consisting of a candle (found to increase the detection sensitivity) held in a small lantern fixed to a tinned iron funnel and fastened to the end of a 10-foot deal rod. To the lower end of the funnel a brass wire was fastened which could be used to communicate the electricity inside to the cap of the electroscope (figure 3). This must have been an interesting spectacle for the locals as their curate carried it about.12

           For the detection of even smaller charge, Bennet found that he could use Volta’s condenser. In 1778, Volta had announced the invention of the electrophorus which was a ‘perpetual’ electrical creator consisting of a dish of metal containing the dielectric cake, a wooden shield covered with tin-foil and an insulating handle. The dielectric cake was a mixture of turpentine, resin and wax. Operation was simple. The plate was

    Figure 3. The deal-rod apparatus for detecting atmospheric electricity, a device for diffusing powders to reveal their charges, and other of Bennet’s apparatus described in the New Experiments

    charged from a machine and then discharged by touching the shield and plate together or alternately. When the shield was removed its negative charge could be given to the hook of a Leyden jar, then replaced, touched, brought back to the hook, etc., until the condenser was sufficiently charged. Volta’s condenser was in fact an electrophore that had a layer of varnish as cake. Bennet used both the larger and smaller of Volta’s condensers remarking on their ‘amazing power’. The idea of using both was actually Cavallo’s, but, even with both, Bennet found that some charges still could not be detected. Solving this problem led to his second important invention, the doubler of electricity.13

           The discovery of the doubler was announced in a paper sent to the Royal Society by Reverend Richard Kaye, F.R.S., in 1787. This instrument, the ‘simple doubler’, consisted of two polished brass plates (B and C) with insulating handles one in the middle and the other on the side (figure 2). The plates were varnished on the underside, with the handles insulated by glass covered with sealing wax. Collected electricity in the Leyden jar was applied to the cap of the gold-leaf electroscope upon which was placed the plate B, touching it with the forefinger stretched over the insulating nut. Thus the electricity ‘spreads upon the cap’, which served as a condensing plate and electrified the plate B contrarily (because it was earthed) with the varnish interposed as a charged electric.14 The jar was then removed and the forefinger lifted up. The plate B was separated from the cap and the plate C placed on its upper side and touched by stretching a finger over the nut of its insulating handle. Then the last plate was electrified contrary to B, and the finger was removed with the plate C separated from B. It would then be evident ‘to electricians that the electricity of the cap and that of the plate C will be of the same kind, and nearly of equal quantity’.15 Thus the original charge was effectively doubled. Next the edge of the plate C was applied to the side of the cap, and touching and placing B as before, the electricity of C and that of the cap both acted on the plate B. The result was that in Bennet’s terms, the ‘intensity’ of its contrary electricity became equal to both. When C was removed in an unelectrified state, and the forefingers were taken off from B, then B was lifted up. Once C had been placed upon it, the process could proceed as before, repeated until the gold leaves diverged. Bennet took the fact that the gold leaves diverged about twice the distance on each operation as a rough indication that the electricity was being doubled.

           There were problems. Cavallo announced that though the merit of Bennet’s invention was considerable, the use of it was ‘far from precise and certain’ and it was ‘not an instrument to be depended upon’.16 The primary purpose of the doubler was manifesting small charges by augmentation, but it was found that the doubler produced electricity even when no charge was given to it in the first place. Suspecting friction to be a cause, Cavallo designed a collector of electricity which needed no touching during doubling. Bennet too had noticed the problem of adherent or ‘spontaneous’ charge and suspecting friction, and tried to devise a doubler with sliding or revolving parts. But before he had finished, William Nicholson, a London teacher and instrument maker, sent him an ingenious revolving doubler that he had constructed. This consisted of two insulated and immovable plates about 2 inches in diameter and a moveable plate, also insulated, which revolved in a vertical plane parallel to the two other plates passing alternately (figure 4). A ball ‘I’ was made heavier on one side than the other and placed on the axis opposite the handle to counterbalance plate B so it could be stopped at any part of its revolution. The plate A was constantly insulated and received the communicated electricity. Plate B revolved and when opposite to plate A, the connecting wires at the end of the crosspiece D touched the pins of A and C at EF. A wire proceeding from the plate B touched the middle piece G, which was supported by a brass conducting pillar in connection with the earth. In this position, if electricity was given to A, then B would acquire a contrary state and revolving

    Figure 4. Nicholson’s revolving doubler.

    further—the wires also moving with it by means of the same insulating axis—the plates were again insulated till the plate B was opposite to C. Then the wire at H touched the pin on C, earthing it and giving the same kind of electricity as that of A.17 By moving the handle still further, B was again brought opposite to A with the connecting wires joining A and C. These both acted on B, which was earthed as before hence nearly doubling ‘its intensity’. Simultaneously, the electricity of C was absorbed into A because of the increased capacity of A while opposed to B. This was capable of acquiring a contrary state because it was earthed ‘sufficient to balance the influential atmospheres of both plates’. By continuing to revolve the plate B the process was performed ‘in a very expeditious and accurate manner’.18

           Nicholson’s doubler was found by Bennet to still retain its spontaneous charge, which he thought was due to ‘the increased capacity’ of approximating parallel plates that ‘might attract and retain their charge tho’ neither of them were insulated’.19 The idea that substances always contained a residual charge either positive or negative, regardless of whether they were insulated or not, proved to be a very fruitful line of research. Bennet tried various methods to deprive the doubler of all spontaneous charge, such as earthing and rapidly rotating it before any experiment. In one experiment a copper plate was applied to plate A while A and B were parallel (so that B was earthed). After only five revolutions of B the gold leaf diverged negatively by a quarter of an inch. But where was this electricity coming from? Bennet concluded that different substances had different ‘adhesive affinities’ to the electrical fluid. They could be either positive or negative, the charge being attracted by the position of different plates in parallel.20 After finding that different types of flower on the plates could change the charge produced, he drew the following pregnant conclusion:

    It easily occurred, that if the spontaneous electricity in the beginning of the process was sufficiently weak, the mere contact of metals or other substances having a different adhesive affinity with the electrical fluid might also change it.21

           This was a momentous discovery in the history of electricity, and Bennet confirmed his supposition in a series of experiments with different substances. First, with the plate B parallel to A but insulated, A was touched with a steel blade and B touched with softened iron wire. After 16 revolutions the gold leaf diverged positively. On reversal of the experiment, with the knife applied to B and the soft wire to A, negative charge was registered. Similarly, other metals were applied to the plates and the charge doubled. Reversal of the metals changed the state of the final charge; therefore Bennet proved to his satisfaction that the metals were causing the charge.

           Various single metals were then tested on different plates. In one experiment the metal was applied to plates A and C and the crosspiece, then to plate B with B standing in the lower part of its plane. The results of these single contact experiments were twofold and of crucial importance. Bennet had identified a method of determining the nature of the ‘adhesive affinity’ of electricity to different metals, in other words, the natural electrical state of metals. Second, as the number of revolutions approximated inversely to the strength of the ‘adhesive affinity’, then metals could in theory be graded according to the strength of affinity. When lead ore was applied to plates A, C and the crosspiece, positive electricity was registered. Zinc produced negative charge, so the ‘adhesive affinity’ was positive for lead ore and negative for zinc. Gold, silver, copper and brass were also found to be positive, while tin and zinc were negative. Bennet widened his theory to include non-metal substances with pure antimony, bismuth, tutenag, and different woods and types of stone producing positive charge. He proved that the shape of the substance affected the strength of the charge registered, with thin plates of zinc being stronger than a large lump.22

    BENNET AND VOLTA
           Bennet’s research had an important influence on Volta in the formulation of his contact theory, though Volta had already influenced the British electricians. Bennet, Cavallo and Nicholson had met Volta in London in 1782 when he demonstrated the work of his condenser during a European tour.23 In the Commentarius of 1791, Luigi Galvani (1737-1798) demonstrated how frogs’ legs jerked under certain electrical conditions, such as when touched by metals. This was taken as proof that an animal electricity existed which was secreted by the brain and distributed through the nerves causing motion. Volta disagreed, arguing that the mere contact between metals generated a charge, with animal parts being unnecessary, and proceeded to rank metals according to their electromotive power; he wondered, like Bennet, if metals were mere passive agents. Indeed the frogs’ legs served for Volta an analogous position to that of the revolving doubler in Bennet’s experiments. Volta found that two metals in contact with the legs produced no convulsions, unlike one metal. After various experiments, including the application of metals to the tongue (producing an acid taste), Volta made this explicit statement: ‘Metals are thus not only perfect conductors, but motors of electricity.’ The earliest announcement of this theory was June 1792, three years after Bennet’s New Experiments had been published.24 From 1796, Volta dispensed with the frogs’ legs for good, using Nicholson’s doubler instead to detect small contact charge. In one conclusive experiment, metal strips of zinc and silver were held together and allowed to touch a condenser plate, with negative charge being registered. He then used Nicholson’s doubler to test the effects of two metals in contact. These experiments led to the invention of the pile, which was thought by Volta to be decisive proof that Galvani was wrong. Thus the letter to Banks was entitled ‘On electricity generated by the contact of conducting substances’ and Volta paid little attention to the chemical effects of the pile.25

    Nicholson, the inventor of the revolving doubler wrote that:

    With regard to the principle of the electric-motors of Signor Volta, I must observe that Bennet made many direct experiments by the application of different metals, by the single contact and double touch, to the plates of the doubler, followed by the production of electricity, which were published in his New Experiments ...

    He did not know the date of Volta’s experiments but believed them:

    to be much later than those of the same kind by Bennet. This last philosopher, as well as Cavallo appears to think that different bodies have different attractions or capacities for electricity 26

           Cavallo’s experiments were made after Bennet, so that as Nicholson indicated, it was Bennet who anticipated Volta’s concept of electromotive potential. Volta’s experiments with the doubler, notably those using different metals in contact, were strikingly similar and other contemporaries recognized this, including Davy and Darwin.27 Bennet’s concept of adhesive affinity was similar to Volta’s electromotive potential of substances. When he spoke of the fact that ‘the mere contact of metals or other substances having a different adhesive affinity with the electrical fluid might also change it’ and the ‘method of single contact’ which ‘appeared to cause a positive charge’28 this equated to Volta’s electromotivity. Only the terminology was different. Certainly Volta was a much greater experimenter and his formulations were more precise; but when he investigated the electromotive potential of metals and other substances he was following a lead already taken by Bennet, who had extended his concept of ‘adhesive affinity’ to non-metals such as wood, and substances such as bismuth, antinomy and tutenag. These he had then graded according to the strength of their adhesive affinity.

           Doubtless Volta’s primary motivation for investigating contact properties came from the rivalry with the Galvanists. In 1792 Volta stated that ‘Metals are thus not only perfect conductors, but motors of electricity … This is a new virtue of metals, which no one has yet suspected, and which I have been led to discover’.29 This was three years after Bennet’s book, which if Volta had closely read would have prevented him from making this statement. Therefore the relationship between Volta and Bennet is not straightforward. Volta subscribed to the New Experiments, but may have not read it until 1795, or perhaps he read it quickly and was only reminded of it after Cavallo’s work. Whatever the precise details, the closeness of Volta’s experiments with the doubler to those undertaken by Bennet confirm the influence, as does Volta’s own tribute to Bennet in the letter to Banks announcing the discovery of the pile.30

    BENNET’S PHILOSOPHICAL CIRCLE
           The New Experiments subscription list demonstrates the breadth of Bennet’s scientific contacts. The most important relationships were with the Lunar Society and various Derbyshire philosophers, notably Erasmus Darwin. From the middle of the 18th century groups of professionals, prosperous traders and philosophers came together in different provincial towns to form societies that had scientific and literary aspirations. Their appearance reflected the new economic prosperity and importance of many Midland towns, which enjoyed a growth in population and geographical area. Bennet’s own Wirksworth was at the centre of the Derbyshire lead mining industry, which had enjoyed a boom in the 18th century. The construction of fashionable classical houses and public buildings, the beginnings of industrialization and the deliberate emulation of London culture all marked the onset of a provincial urban renaissance. The ideal of scientific education was prized—often as a mark of social success—by the middle classes and was satisfied by the philosophical societies and roving itinerant lecturers who advertised in the local press, delivering courses for those who could afford it. The most important of the Midland societies were the Lunar Society and the Derby Philosophical Society.31

           Robert Schofield has described the Lunar Society as:

    A brilliant microcosm of that scattered community of provincial manufacturers and professional men who found England a rural society with an agricultural economy and left it urban and industrial.32

           The original members of the Lunar Society included: Darwin; John Whitehurst; Matthew Boulton (1728-1809), mechanical engineer; William Small (1730-1775), physician, chemist and machinist; Josiah Wedgwood (1730-1795), industrialist and chemist; Richard Lovell Edgeworth (1744-1817), author and philosopher; and James Watt (1736-1819), chemist and engineer. Other members included Thomas Day, James Keir and Joseph Priestley (1733-1804). Most of these subscribed to Bennet’s New Experiments and supported his election to the Royal Society in 1789. Priestley was an English Unitarian minister from Leeds who attended a Dissenting academy in Daventry, later teaching at the Warrington Academy. A meeting with Franklin and other London electricians inspired his electrical work culminating in the History of Electricity (1767). He moved to Birmingham in 1780, where he continued to work on airs and wrote controversial philosophical and theological books. The Lunar Society

    Figure 5. Electrical pattern made with an electrophorus and formed from powdered resin

    crystallized during the 1760s, though some of the members, such as Darwin, Boulton and Whitehurst, already knew each other. It was known as the Lunar Society because they met at member’s houses once a month in the afternoon of the Monday nearest the time of the full moon. The Society was informal and had no fixed rules or constitution. Even if it is an exaggeration to talk of these men as having ‘manipulated a revolution’, they were certainly a successful group of technological and scientific innovators. Wedgwood founded a pottery business, and the Boulton and Watt steam engines that emerged from their Soho plant were more efficient then previous designs. This was a unique period in British history when an aspiring middle-class intelligentsia helped to make provincial science and industry of paramount importance, though in blurring the distinction between inventor, manufacturing process and final product, they tended to ignore the oppressive realities and social dislocation of the new ‘satanic mills’. This was the context of Bennet’s work.33

           Priestley received the dedication of Bennet’s 1786 paper on the gold-leaf electroscope, which already had ‘the honour’ of his ‘approbation’. Bennet had carried his electrometer ‘from Birmingham to London, [and] another from Wirksworth to Etruria in a portmanteau on horseback, yet without injury’.34 This was a tour of the Lunar map, taking in Derby, Birmingham and Wedgwood’s Etruria. Bennet used an electrophorus to create Lichtenburg figures—beautiful patterns made on the resinous electrophorus by drawing over it the knob of a charged glass—which were shown by projecting fine powdered resin over the plate. One such figure was represented in the New Experiments’ frontispiece (figure 5). Wedgwood had the idea of commercially producing the figures by using fine powdered enamel instead of resin and then baking the plate or vessel, hence Bennet’s visit to Etruria.35 In 1785, John Southern, one of the ‘Soho Group’ of Birmingham inventors and industrialists, published A Treatise Upon Aerostatic Machines, one of the earliest English books on balloon construction. He was a ‘special subscriber’ to Bennet’s New Experiments and included in his treatise a description of a process for manufacturing inflammable air and a method of pasting sheets together for making experimental paper balloons given to him by Bennet. In Bennet’s notebook there is evidence that he worked on the problems of lighting, likewise a Lunar interest. He recorded a design for ‘a convenient fountain lamp’ using a glass vial placed in a socket of tin with the neck downwards and a looking glass to concentrate the light which was illustrated with five drawings. From about 1784 to 1786, lamp designs often featured in Lunar correspondence. Aimé Argand (1755–1803) had created a new oil lamp incorporating a tubular wick and glass chimney. An upward draught of air reduced smoke and smell while increasing the light. Boulton and Watt became involved in the manufacture and Wedgwood corresponded with Darwin on the subject of creating marketable lamps.36 Nicholson, the creator of the revolving doubler, was also closely involved with the Lunar Society, having worked for Wedgwood’s pottery company and been a member of J.H. Magellan’s London Philosophical Society in the 1780s with Wedgwood, Whitehurst and other Lunar Members who travelled to London.37

           Darwin was the most important of Bennet’s philosophical friends. A successful physician, inventor and writer, Coleridge said that ‘Dr Darwin possesses perhaps a

    Figure 6. Bennet’s pendulum doubler as pictured in Erasmus Darwin’s Phytologia

    greater range of knowledge than any other man in Europe, and is the most inventive of philosophical men. He thinks in a new train on every subject except religion’.38 Darwin’s letters and books reveal a close collaboration between himself and Bennet during the 1780s. Darwin had invented a mechanical doubler, which he passed to Bennet for development, and he continually praised Bennet’s work in his books, probably encouraging Joseph Johnson the publisher to sell the New Experiments in London. Darwin had known Franklin since the 1750s and in his last letter to him of 1787, he described Bennet’s doubler.39 In the Zoonomia, Darwin singled out Bennet’s ‘ingenious’ experiments with metals and the doubler, calling it ‘the greatest discovery made in that science since the Coated Jar and the eduction of lightning from the Skies’.40 In The Temple of Nature, Darwin again described the doubler and associated the metal contact experiments with galvanism and Volta’s pile. Darwin’s first Royal Society paper had concerned electricity, being an attempt to refute a theory that cloud formation was only the result of the electric fire forcing vapour particles into the air and that rain was the result of the loss of electricity—hence lightning.41 Later he argued that cloud formation was due to adiabatic expansion, the expansion of a gas (in this case water vapour) from a region of high pressure to a region of low pressure; in conditions of low pressure heat was removed from the water, which then condensed to form precipitation. By contrast, in the New Experiments, Bennet tended to stress the electrical origins of various natural phenomena, such as weather conditions, the aurora borealis and meteors. He confirmed that ascending water vapour was electrified positively and so felt justified in interpreting lightning as the release of the charge from

    Figure 7. Bennet’s magnotometer, which utilized spider’s thread

    clouds and therefore the cause of rain.42

           Darwin dealt extensively with electrical phenomena in The Economy of Vegetation, ranging from Bennet’s electroscope to electrical fish and lightning. The creation of the electroscope and the doubler were partly motivated by Darwin, as Bennet recorded:

    I therefore contrived the following doubler for the purpose of more easily making an electro- meteorological diary, which I undertook at the request of my friend Dr Darwin, who hoped that from thence some light might be thrown on the causes of the sudden changes of aerial currents, a circumstance of so much importance to the early growth and maturity of vegetation.43

           Together they investigated the role of electricity in the germination and growth of plants. In Phytologia, Darwin suggested that water was decomposed into oxygen and hydrogen by the action of electricity in plants, ‘by the decomposition of water in the vegetable system when the hydrogen unites with carbon and produces oil, the oxygen becomes superfluous, and is in part exhaled’.44 To test this hypothesis, a Leyden jar or revolving doubler were of no use, because the supply needed to be continuous, so Bennet invented the pendulum doubler portrayed in Phytologia, which kept the flower pots ‘perpetually subject to more abundant electricity’ (figure 6). The device incorporated three plates, two of which were fixed and a third that swung between them. A system of springy wires completed connections during different stages of the doubling process. The loose plate swung from the pendulum of a Dutch wooden clock and electricity was passed to the plant pot via another connection.45

           Analogies and shared concepts and terminology abound in the works of both Bennet and Darwin, such as the analogy of a cork smeared with oil placed on water as an illustration of electricity flowing from points, which first appeared in Bennet’s notebook and then in Darwin’s Economy of Vegetation and was used again in The Temple of Nature.46 But Bennet was an individual philosopher and not merely an actor reading a Darwinian monologue. Their magnetic theories reveal an interchange of ideas and a theoretical divergence between the two. In his final Royal Society paper, Bennet announced the discovery of a magnetometer for the detection of minute forces (figure 7). Previous magnetometers had used materials that twisted out of shape, such as cotton; but Bennet’s utilized spiders thread,47 which had remarkable tenuity and once took 18,500 revolutions before the thread broke, with the line never deviating from the meridian. Darwin borrowed Cavallo’s book on magnetism from the Derby Philosophical Society library and asked Bennet to investigate Cavallo’s claim that inflammable air caused magnetism using the magnetometer. Later ‘at the request of Dr Darwin’ Bennet repeated another experiment of Cavallo’s which claimed that iron filings increased their magnetic attractions by effervescence with diluted hydrochloric acid. Cavallo, Bennet and Darwin were testing the degree to which chemical changes induced by heat could effect electric or magnetic forces.48

           Darwin had been primarily responsible for the foundation of the Derby Philosophical Society in 1783. Members subscribed to Bennet’s New Experiments both individually and collectively, though he never joined. The membership of the Derby Society, which was dominated by medical men, included: Brooke Boothby, the poet, philosopher and political theorist; Robert Bage the radical novelist; William Strutt (1756–1830), the inventor and industrialist (later F.R.S.); and individuals from the Wedgwood and Evans industrial families. Other local philosophers included the geologist John Whitehurst, F.R.S. (1713–1788), and James Pilkington, the radical minister and author of A View of Derbyshire (1789), which described the geology, antiquities, industry and botany of the county.49 During the 1790s, Darwin and Strutt moved away from Bennet’s Franklinist unitarian position towards a dualist electrical theory. This situation was mirrored by magnetism. In The Temple of Nature Darwin advocated two magnetic fluids, an ‘arctic’ and an ‘antarctic’, partly on the basis of a kind of symmetry with his electrical dualism.

           Bennet and Darwin favoured different earthquake theories. After an earthquake in November 1795 that appeared to centre on Derbyshire and Nottinghamshire, Bennet sent an account to the Royal Society which was printed in a paper by Gray. Bennet suggested that the:

    circumstances seem to favour the supposition of earthquakes being caused by electricity, but it is only from a collection of numerous facts, that any rational theory can be formed upon the subject.50

           The theory that earthquakes were caused by electricity had been held by the antiquarian William Stukeley and repeated by Priestley. Evidence for the electric origins of earthquakes was said to include the appearance of fireballs—one of which had reportedly been seen at Derby—wind direction, the fact that vegetables grew more quickly, the sight of a bright aurora borealis and even medical complaints. Bennet wrote for more descriptions of the earthquake to his Derbyshire friends including Reverend Peach of Edensor, John Chatterton of Derby and White Watson of Bakewell. The Chattertons, John I (1742–1800) and John II (1771–1857), were plumbers and glaziers living in Derby. John II, presumably Bennet’s correspondent, was a chemist, inventor, friend of Darwin and member of the Derby Philosophical Society.51 White Watson (1760–1835) was a geologist, fossil dealer and lecturer who supplied specimens to Darwin, Wedgwood, Strutt, Alexandre Brogniart in Paris and Joseph Banks (1743–1820), the President of the Royal Society, who had an estate in Derbyshire. Watson produced stratigraphical sections of Derbyshire inlaid with actual rock and mineral samples. He was a corresponding member of the London Mineralogical Society and the author of A Delineation of the Strata of Derbyshire (1811).52

           In The Economy of Vegetation, Darwin had described the earth as a ‘large mass of burning lava’ in ‘basaltic caves imprisn’d deep’ with ‘vaulted roofs of adamantine rock’.53 He argued that the evidence for the existence of the ‘billowy lavas’ came from the heat found in mines and his own observations on warm springs such as St Anne’s Well at Buxton, which he contributed to Pilkington’s View of Derbyshire. Whitehurst held that volcanic activity deep in the Earth’s crust caused many geological phenomena. Strata were thrust up into mountains and the size and depth of oceans, rivers and valleys were the result of pressure from these forces.54 Darwin accepted this position and following Whitehurst saw evidence in the geology of Derbyshire. It was these ‘central fires’ of fluid lava that caused earthquakes, like a stroke on liquid in a bladder which would be felt on the other side. Thus Bennet and Darwin had different views of the causes of earthquakes, with Bennet suggesting electricity to be involved while Darwin saw heat from fluid lava to be important. Related to this, the two had different theories about the cause of the Earth’s magnetism, Darwin holding that molten iron in the Earth’s core caused the field, while Bennet thought that a magnetic atmosphere existed over the Earth, being rarified at one pole and condensed at the other.55 An electrical theory for earthquake origin was less ideologically challenging than a gradualistic developmental geological theory based on central volcanic fires which challenged the Mosaic account.

    CONCLUSION
           Bennet was a clergyman who owed his position to patronage. He was dependent on his contacts in the church for his living and for the publication of his scientific research. His most important patrons included: Reverend Richard Kaye, F.R.S, Dean of Lincoln and Vicar of Wirksworth; Joseph Banks; the Dukes of Devonshire and Bedford; George Adams, the instrument maker to George III; and members of the Gell family, the local Wirksworth gentry of Hopton Hall. Bennet also managed to obtain the support of other provincial philosophers, notably the Derby philosophers and members of the Lunar Society. The Royal Society served as the official forum for the announcement of his discoveries and sanctioned their authenticity in the scientific community. However, Bennet’s researches ended abruptly by the mid-1790s due to ill health and possibly because the balancing act between support from radicals such as Darwin and Priestley and ‘establishment’ figures such as Banks and Richard Kaye was no longer tenable. British provincial science suffered in the 1790s because of its association with radicalism. This had been heightened by the French Revolution and forced the only Anglican member of the Derby Philosophical Society to resign in 1791. Bennet was among those who signed a loyalist petition against Jacobinism with his patrons the Gells in 1795.56 Two years before, an address of the Derby Society for Political Information, whose membership included some of his erstwhile supporters such as Darwin and the Strutts, had been condemned by the Government as seditious and libellous.57

    ACKNOWLEDGEMENTS
           I am grateful to Linda and the staff of Derby Local Studies Library for their assistance, and to Mr Michael Handley of Wirksworth for sharing some of his knowledge of Bennet’s personal background and showing me the portrait. Professor W.H. Brock, then of the University of Leicester, read through an early draft and made some useful criticisms.

    NOTES
  1. A. Volta, ‘On the electricity excited by the mere contact of conducting substances of different kinds’, Phil. Trans. R. Soc. Lond. 90, 403–431 (1800), English translation from, W. Ostwald, Electrochemistry; History and Theory, (Leipzig, 1896), translated by N.P. Date, pp. 115–141 (Washington, 1980).

  2. D.C. Witt, ‘Abraham Bennet’, Dictionary of National Biography, Missing Persons, p. 58 (Oxford University Press, 1993), written with the assistance of Michael Handley.

  3. Derby Mercury (5 July 1826), Derby Reporter (6 July 1826).

  4. D.C. Witt, op. cit., note 2.

  5. No record of Bennet has been discovered in the registers of Cambridge, Oxford, Dublin, Aberdeen or Glasgow universities.

  6. A. Bennet, memoranda miscellania, mss., Derby Local Studies Library.

  7. Derby Mercury (23 May 1799). The bicentenary of Bennet’s death is to be commemorated by a special service on 6 May 1999, at St Mary’s Church, Wirksworth.

  8. A. Bennet, New Experiments on Electricity Wherein the Causes of Thunder and Lightning are Explained… Also, A Description of a Doubler of Electricity… (Drewry, Derby, 1789), prefaced by a list of over 400 subscribers; A. Bennet, ‘Description of a new electrometer’, Phil. Trans. R. Soc. Lond. 76, 26–34 (1786); A. Bennet, ‘An account of a doubler of electricity’, Phil. Trans. R. Soc. Lond. 77, 288–296 (1787); A. Bennet, ‘A new suspension of the magnetic needle invented for the discovery of minute quantities of magnetic attraction’,

    Phil. Trans. R. Soc. Lond. 82, 81–98 (1792); generally see, F.W. Shurlock, ‘Abraham Bennet FRS’, Science Progress, 452–464 (1925); W.C. Walker, ‘The detection and estimation of electric charges in the eighteenth century’, Annals of Science 1, 66–100 (1936); D. King-Hele, Doctor of Revolution, the Life and Genius of Erasmus Darwin, pp. 117, 179 (London, 1977); W. Ostwald, Electrochemistry, pp. 74–86, trans. Date; R. Schofield, The Lunar Society of Birmingham: a social history of provincial science and industry in eighteenth-century England, pp. 8, 166, 275 (Oxford, 1963); J. Heilbron, Electricity in the 17th and 18th Centuries: a study of early modern physics, pp. 450–451, 457–458 (California, 1979); P.L. Mottelay, A Bibliographical History of Electricity and Magnetism, pp. 289–291 (London, 1922).

  9. Heilbron, op.cit, note 8, pp. 312–334; Walker, op. cit., note 8, pp. 70–72.

  10. J. Priestley, The History and Present State of Electricity, with Original Experiments, pp. 455–479 (London, 1767); Heilbron, op. cit., note 8, pp. 337–339, 384–387.

  11. T. Cavallo, ‘Some new experiments in electricity with the description and use of two new electrical instruments’, Phil. Trans. R. Soc. Lond. 70, 15–29 (1780); A. Bennet, ‘Description of a new electrometer’, Phil. Trans. R. Soc. Lond. 76, 26–34 (1786).

  12. Bennet, New Experiments…, op. cit., note 8, pp. 112–114 and plate III.

  13. Heilbron, op.cit., note 8, pp. 412–417, 457; Bennet, op. cit., note 11, p. 32.

  14. Bennet, ‘An account of a doubler…’, op. cit., note 8, pp. 289–291; New Experiments…, op. cit., note 8, pp. 75–79.

  15. Bennet, New Experiments…, op. cit., note 8, p. 78.

  16. T. Cavallo, ‘Of the methods of manifesting the presence, and ascertaining the quality of small quantities of natural or artificial electricity’, Phil. Trans. R. Soc. Lond. 78, 2 (1788).

  17. W. Nicholson, ‘A description of an instrument which by the turning of a winch, produces the two states of electricity without friction or communication with the earth’, Phil. Trans. R. Soc. Lond. 78, 403–407 (1788); Bennet, New Experiments…, op. cit., note 8, p. 83.

  18. Bennet, New Experiments…, op. cit., note 8, p. 83.

  19. Bennet, New Experiments…, op. cit., note 8, p. 83.

  20. Bennet, New Experiments…, op. cit., note 8, pp. 83–89.

  21. Bennet, New Experiments…, op. cit., note 8, p. 91.

  22. Bennet, New Experiments…, op. cit., note 8, pp. 97–100.

  23. Walker, op. cit., note 8, pp. 82–84.

  24. L. Galvani, De Viribus electricitatis in motu musculari commentarius cum Joannis Aldini dissertatione et notis, (Modena, 1792); M. Pera, The Ambiguous Frog: the Galvani-Volta controversy on animal electricity, translated by J. Mandelbaum, p. 111 (Princeton, 1992).

  25. Ostwald, op. cit., note 1, p. 126.

  26. C.H. Wilkinson, Elements of Galvanism in Theory and Practice, vol. II, p. 23 (London, 1804).

  27. E. Darwin, The Temple of Nature: or the origin of society, additional note, pp. 50, 62 (Johnson, London, 1803); H. Davy, ‘Bakerian lecture, on some chemical agencies of electricity’, Phil. Trans. R. Soc. Lond., 97, 1 (1807).

  28. Bennet, New Experiments…, op. cit., note 8, pp. 91, 100.

  29. Pera, op. cit., note 24, p. 111.

  30. A. Volta, ‘On the electricity excited by the mere contact of conducting substances of different kinds’, Phil Trans. R. Soc. Lond. 90, 431 (1800).

  31. R.P. Sturges, ‘The membership of the Derby Philosophical Society 1783–1802’, Midland History, 4 (1978); E. Robinson, ‘The Derby Philosophical Society’, Ann. Science, 9, 359–367 (1952).

  32. Schofield, op. cit., note 8, p. 3.

  33. M. McNeil, Under the Banner of Science, Erasmus Darwin and His Age, 14–24 (Manchester University, 1987).

  34. Bennet, New Experiments…, op. cit., note 8, p. 21.

  35. Bennet, New Experiments…, op. cit., note 8, p. 50

  36. Schofield, op. cit., note 8, pp. 252–253; D. King-Hele (ed.) The Letters of Erasmus Darwin, letters to Wedgwood, pp. 169, 170–171 (Cambridge University Press, 1981).

  37. Musson and Robinson, Science and Technology In the Industrial Revolution, pp. 126–127 (Manchester, 1969); E. Robinson, ‘R.E. Raspe, Franklin’s club of thirteen and the Lunar Society’, Ann. Sci. 11 (1955); S. Lilley, ‘Nicholson’s Journal’, Ann. Sci. 6, 78–101 (1948–50).

  38. E.L. Griggs (ed.), The Collected Letters of Samuel Taylor Coleridge, vol. I, p. 99 (London, 1956–59); for Darwin see, D. King-Hele, Doctor of Revolution (London, 1977); McNeil, op. cit., note 33; D. King-Hele, Erasmus Darwin and the Romantic Poets (London, 1986); D. King-Hele (ed.) The Essential Writings of Erasmus Darwin (London, 1968); D. King-Hele, Erasmus Darwin: a life of unequalled achievement (de la Mare, 1998).

  39. E. Darwin, letter to Franklin, 29 May 1787, King-Hele (ed.) op. cit., note 36.

  40. E. Darwin, Zoonomia; or the Laws of Organic Life, vol. I, p. 120 (Johnson, London, 1794).

  41. E. Darwin, ‘Remarks on the opinion of Henry Eeles Esq., concerning the ascent of vapour’, Phil. Trans. R.. Soc. Lond.. 50, 240–254 (1757).

  42. Darwin, op. cit., note 27, additional note XII, pp. 46–79; E. Darwin, ‘Frigorific experiments on the mechanical expansion of air’, Phil. Trans. R. Soc. Lond. 78, (1788); King-Hele, Doctor of Revolution, op. cit., note 38, p. 184.

  43. E. Darwin, The Botanic Garden: a poem in two parts: Part I: the Economy of Vegetation (Johnson, London, 1791); Bennet, ‘An account of a doubler of electricity’, op. cit., note 8, p. 289.

  44. Bennet, ‘An account of a doubler’, op. cit., note 8, p. 289; Darwin, Phytologia: or the Philosophy of Agriculture and Gardening, p. 194 (Johnson, London, 1800).

  45. Darwin, op. cit., note 44, p. 312.

  46. Bennet, memoranda miscellania, 136; Darwin, op. cit., note 43, note XIII, p. 25; Darwin, op. cit., note 27, additional note XII, p. 52.

  47. In 1775 Gregorio Fontana had suggested that spider’s thread be used as a substitute for wires, Mottelay, A Bibliographical History of Electricity and Magnetism, p. 290.

  48. A. Bennet, ‘A new suspension of the magnetic needle’, Phil Trans. R. Soc. Lond. 82, 81–82, 92–96 (1792); King-Hele, op. cit., note 36, letter to Thomas Beddoes, pp. 173–174.

  49. J. Whitehurst, Enquiry into the Original State and Formation of the Earth, 1st edn (London, 1778); J. Pilkington, A View of the Present State of Derbyshire, 2 vols (Drewry, Derby, 1789).

  50. E.W. Gray, ‘Account of an earthquake felt in various parts of England, November 18, 1795: with some observations thereon’, Phil. Trans. R. Soc. 86, 361 (1796).

  51. S. Glover, History and Gazeteer of the Town of Derby, vol. II, p. 601 (Derby, 1833); Derby Mercury (2 October 1832); Derby Philosophical Society cash ledger (1813-1845) mss. 7625, Derby Local Studies Library; Derby Local Studies Library, queries answered 153 (1966).

  52. T. D. Ford, ‘White Watson (1760–1835) and his geological sections’, Proc. Geol. Assoc. 71 (1960).

  53. Darwin, op. cit., note 43, canto I, l. 137–142, additional note VI.

  54. J. Whitehurst, Enquiry (1778).

  55. Gray, op. cit., note 50, pp. 353–381; Darwin, op. cit., note 27, additional note XII, pp. 68–72; Bennet, ‘A new suspension of the magnetic needle…’, op. cit., note 8, p. 92. For later researches in Palaeomagnetism, notably evidence for the reversal of the earth’s magnetic field, see, P. Bowler, The Fontana History of the Environmental Sciences, pp. 413–416 (London, 1992).

  56. Derby Mercury (3 December 1795); A letter from Richard French to William Strutt apparently dated August 1792, urged Strutt to persuade Darwin that a local clergyman ‘Mr. B’ should not be recommended for preferment to Sir Francis Burdett as he was ‘not even a Whig in politics’, ‘superstitiously religious’ and had signed an address in support of the war whilst urging his scholars to do likewise. Given that Bennet signed a loyalist address, sought preferment and was a schoolmaster, this may have been him, but this cannot be confirmed as the letter is now missing from the Strutt correspondence in Derby.

  57. Address to the Friends of Free Enquiry and the General Good, Derby Society for Political Information, broadsheet (Derby, December 1791); D. King-Hele, ‘The 1997 Wilkins Lecture: Erasmus Darwin, the Lunaticks and evolution’, Notes Rec. R. Soc. Lond. 52, 153–180 (1998).



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