Throughout the latter half of the eighteenth century, Benjamin Franklin spent his time on more than just revolutionary printing, diplomacy, and the politics surrounding the emergence of the American Revolution; he was also the leading authority on electrical studies. His theory of electrical charge, first published in 1751, became the dominant explanation throughout the transatlantic scientific community because of its clarity and explanatory power.Footnote ¹ Franklin applied his theories to the practical problem of lightning protection, designing a conductor that used a pointed metal rod connected to the ground by metal wires to divert lightning strikes and reduce their likelihood. Based on experimental evidence and investigations of buildings damaged by lightning, his design was widely adopted on churches, homes, and public buildings throughout Britain, France, and Britain’s North American colonies.Footnote ²

There was a clear scientific consensus by the early 1770s that Franklin was the undisputed expert in electrical matters. It was thus no surprise that in 1772, during the fifteen years he lived in London, Franklin served on a Royal Society committee charged with protecting the Royal Gunpowder Magazine at Purfleet-on-Thames from lightning. When the magazine was nevertheless struck in 1777, Benjamin Wilson, a portrait painter and Fellow of the Royal Society who had long opposed Franklin’s theory, renewed his public criticisms. Although many in the Royal Society and broader scientific community had previously dismissed Wilson’s objections, the political climate created by the American Revolution gave his attacks on Franklin new force in the context of public opinion. The American Revolution had little impact on the scientific understanding of electricity, but the scientific debate on lightning conductors became a proxy for the political conflict playing out in Britain’s North American colonies. After the Purfleet lightning strike, the scientific community continued to support Franklin. But powerful patrons, including King George III, turned against him. The debates surrounding the lightning strike at the Royal Gunpowder Magazine in May 1777 were not merely an internal scientific squabble. Their timing and the cast of characters involved reveal how the American Revolution both reshaped scientific institutions and shifted the public presentation of science in Britain.

Benjamin Franklin began his electrical studies in the mid-1740s and by 1747 had articulated a single-fluid theory of electricity. Previous experimenters explained electrical attraction and repulsion through two distinct “electrical fluids,” but Franklin argued that a single electrical fluid could exist in either a “plus” or “minus” state, accounting for different electrical effects.Footnote ³ He set out this theory of electrical charge in letters to scientific peers in England in 1747 and published them in Experiments and Observations on Electricity in 1751. At the time, Franklin was a loyal subject of Britain and maintained strong connections with Britain’s preeminent scientific society, the Royal Society of London for Improving Natural Knowledge. In 1753, he received the Royal Society’s highest honor, the Copley Medal, and was elected a Fellow of the Society in 1756. Franklin lived in London from 1757 to 1775 during which time he was an active member of this scientific community.Footnote ⁴

Franklin based his lightning rod design on experiments conducted in 1747. He found that bringing “the point of a long, slender, sharp bodkin” within six or eight inches of an electrified glass rod gradually dissipated its charge without producing a spark, whereas a blunt object had to be brought to within an inch of the rod and always discharged with a spark.Footnote ⁵ He further observed that connecting a pointed conductor to a metal object made it nearly impossible to electrify that object, demonstrating that “points will throw off as well as draw off” electricity.Footnote ⁶ Franklin concluded that electrical charge dispersed most readily from acute points, and showed that electricity will flow off a point “till no more is remaining.”Footnote ⁷ For these reasons, Franklin believed a pointed conductor could “prevent a stroke” of lightning by gradually drawing electrical charge from the atmosphere “or, if not prevented, would conduct it, so as that the building should suffer no damage.”Footnote ⁸ He connected the lightning rod to the earth with a wire, a design informed by both experiment and his investigations of lightning damage. His study of a 1754 strike on a church in Newbury, Massachusetts, showed that lightning had followed existing metal wires from the steeple to the ground, sparing the building despite destroying the wires themselves. Franklin concluded that even a relatively small wire could safely conduct lightning away from a structure, although it might need replacing after a strike.Footnote ⁹

Although Franklin’s conductor design (see Figure 1) gained broad acceptance in the English-speaking world and beyond, it also attracted detractors. In 1750, Benjamin Wilson, an experimental philosopher and celebrated portrait painter, published A Treatise on Electricity, in which he explained his opposition to pointed conductors. Wilson’s experiments confirmed that pointed objects drew electrical charge more readily than blunt ones, shown by demonstrating that a needle’s point reduced electrical attraction and produced weaker sparks than its blunt end.Footnote ¹⁰ He gauged the difference in electrical charge by comparing the strength of the spark thrown in each instance.Footnote ¹¹ Wilson feared that because points accept and discharge electricity more easily, pointed conductors would fail to contain lightning strikes, would discharge electricity violently, and therefore could not protect buildings from damage. Instead, Wilson viewed electrical resistance and charge accumulation as safeguards, advocating blunted or ball-ended conductors connected to thick metal bars, which he believed could hold greater quantities of electrical charge.Footnote ¹² Despite their academic disagreement, Franklin and Wilson seem to have maintained a cordial personal relationship through the 1750s. In 1758 Franklin commissioned Wilson to paint his portrait, which he kept in his Philadelphia home until it was taken during the British occupation of the city which lasted from September 1777 to June 1778.Footnote ¹³

Figure 1.

A demonstration of Franklin’s lightning rod conducted in France in 1752. Engraving from Louis Figuier, Les Marveilles de La Science, vol. 1 (Paris, 1867), 521.

Wilson found limited support in his disagreement with Franklin. In June 1764, lightning struck St Bride’s Church on London’s Fleet Street. Edward Delaval, also of the Royal Society, investigated the damage. In a letter published in Philosophical Transactions, he criticized Franklin’s design by likening the church spire to “an apparatus purposely contrived to draw the lightning from the clouds.”Footnote ¹⁴ Although his own illustration showed the spire was topped by a metal cross rather than a point, Delaval also challenged Franklin’s recommendation that relatively thin wires could safely conduct lightning. He argued that “these effects would have been prevented, if a sufficiently large metallic conductor had been extended from the metal at the top of the spire down to the earth.”Footnote ¹⁵ In the same 1764 issue of Philosophical Transactions, Wilson published an open letter to the Marquess of Rockingham outlining his preferred methods for preventing lightning strikes. Rockingham was a Fellow of the Royal Society, a powerful and well-connected Whig politician, and one of Wilson’s patrons.Footnote ¹⁶ In the letter, Wilson reiterated that pointed conductors were dangerous and should be avoided because they “invite” lightning.Footnote ¹⁷ Instead, he proposed installing a rounded metal bar “inside the highest part” of a building, extending it down the wall into moist ground.Footnote ¹⁸ Any metal atop a building, such as a weathervane or cross, should either be removed or connected to this rounded conductor, he insisted.Footnote ¹⁹ Wilson also criticized Franklin’s relatively thin conductors and the use of existing gutters and downspouts as “accidental or partial conductors.”Footnote ²⁰ Despite these arguments, Wilson gained little support (beyond Delaval). Although a capable experimenter, he explained electrical phenomena through Newtonian aether, a theory that failed to account convincingly for observed electrical effects.Footnote ²¹ Franklin’s experiments, theory, and successful conductors proved more persuasive, making him the accepted authority on electrical science.

In 1772, the Office of Ordnance asked the Royal Society to recommend lightning protection for a new gunpowder magazine at Purfleet-on-Thames in Essex. Benjamin Franklin, Henry Cavendish, William Watson, and Benjamin Wilson served on the committee; of these Wilson alone remained unconvinced by Franklinian electrical theory. Purfleet had been selected in the 1750s to replace the smaller naval powder store at Greenwich.Footnote ²² Although the complex was not complete until 1773, the Office of Ordnance began storing powder at the site as early as 1763, probably spurred by the Seven Years’ War to secure powder stores around London. By 1769, Purfleet with the main depot for the British Navy’s gunpowder.Footnote ²³ When it was completed in 1773, the complex featured five barrel-vaulted brick magazines, as well as a storekeeper’s house, a proof house, a clock tower, gardens, and cottages for workers, all of which were encircled by a security wall.Footnote ²⁴

After investigating the buildings and the grounds at Purfleet, the committee delivered their report in August 1772, advising the use of pointed metal conductors on several of the buildings.Footnote ²⁵ These conductors would connect to the metal gutters and coping already present on the buildings, and bars of iron and lead would be installed to connect these elements to wells dug near the base of each building. This proposed solution was a straightforward application of Franklin’s theory and conductor design. Wilson, of course, disagreed with the other committee members, and attached an official dissent to the committee’s report. He reiterated the arguments he had made in his letter of 1764 and his Treatise on Electricity from 1750. Pointed conductors, according to Wilson, were “solliciting the lightning,” and would “increase the quantity of every actual discharge.” He feared that the committee “may be promoting the very mischief we mean to prevent,” and proposed that blunted conductors would be safer and more effective.Footnote ²⁶

Wilson’s objections met with the usual dismissal from his colleagues at the Royal Society, but this time he went over their heads. Wilson wrote a letter to the surveyor general of Ordnance, the man overseeing the magazine at Purfleet, which was published in December 1772. Wilson opened with the sensational claim that “the difference … between pointed and blunted metal, is as 12 to 1.”Footnote ²⁷ He explained that if a pointed conductor would draw lightning from a cloud 1,200 yards away, a blunted one would only do so at a distance of 100 yards, demonstrating that pointed conductors invite strikes.Footnote ²⁸ Wilson briefly presented Franklin’s idea that pointed conductors dissipate electrical charge and could therefore prevent a lightning strike from ever occurring, but decided to “wa[i]ve entering into” the matter, as he found it “liable to many objections,” which he claimed were too numerous to list.Footnote ²⁹

Franklin did not like to argue on matters of science, preferring his writing and experiments to stand on their own merits.Footnote ³⁰ In this case, however, he drafted a letter in response to Wilson’s attack. Franklin explained that Wilson fundamentally misunderstood the experimental basis for favoring pointed conductors, beginning with Wilson’s “12 to 1” claim.Footnote ³¹ In April 1772, William Henly had investigated the effects of a lightning strike at a chapel in Tottenham Court Road. The incident led Henly to conduct a series of experiments comparing the efficacy of pointed and blunted conductors, which he communicated to Franklin and would later publish in Philosophical Transactions in 1774.Footnote ³² In his experiment, Henly set up two electrometers, one connected to a small pointed conductor, the other to a small, blunted conductor. He then electrically charged a glass globe and brought it toward each conductor in turn. The blunted conductor drew a violent spark when the globe came near it. The pointed conductor, on the other hand, began drawing off electrical charge at a greater distance (as shown by the electrometer), and never threw a spark, as it “drew off the charge imperceptibly.”Footnote ³³

In subsequent experiments, Henly found that a blunted conductor received a spark at a distance of two inches, while a pointed conductor began drawing off electrical charge at a distance of two feet, and could even prevent the blunted conductor from being struck if they were beside one another.Footnote ³⁴ This comparison of two inches to two feet was the source of Wilson’s “12 to 1” comparison, but Henly’s experiment clearly showed that the pointed conductor did not draw a spark from a distance of two feet, but instead began harmlessly dissipating electrical charge at that distance. In his letter Franklin explained that Wilson either misunderstood or intentionally misrepresented the evidence from Henly’s experiment, which actually supported the superiority of pointed conductors.Footnote ³⁵ Franklin did not publish this long letter. Instead, a much shorter letter from the committee was published in Philosophical Transactions: “having heard and considered the objections to our Report, concerning the fixing pointed Conductors to the Magazines at Purfleet … from Mr. Wilson … we find no reason to change our opinion, or vary from that Report.”Footnote ³⁶ Wilson’s objections were investigated and found wanting.

During his lengthy stay in London, outside of his scientific pursuits, Franklin spent his time opposing various taxes imposed on colonial subjects. Initially, Franklin opposed any form of violent revolution, believing that peaceful advocacy would be enough to achieve guarantees of fairer treatment for colonial subjects. However, following the passage of the Stamp Act in 1765, Franklin became steadily more disillusioned with British governance, and steadily more estranged from the political center. In 1772, Franklin received an anonymous delivery of letters written by the governor of Massachusetts, Thomas Hutchinson, asking the British government to dispatch soldiers to suppress rebellion in Boston. Franklin circulated these letters among his colonial peers, and John Adams published them in June 1773, against Franklin’s wishes. Franklin admitted his part in the matter, and in January 1774 was called before the Privy Council. He was accused of deceit and fomenting conflict between the Crown and the colonies. With this significant shift in Franklin’s social and political standing, he departed London in March 1775. The battles of Lexington and Concord happened while Franklin was at sea, and by the end of 1776 he was on a diplomatic mission in Paris.Footnote ³⁷ The political fracturing of Britain’s empire, in which Franklin was participating, created a fundamentally different context in which scientific truth and authority would be debated and understood.

On 15 May 1777, around 6pm, lightning struck a building at the Royal Gunpowder Magazine at Purfleet-on-Thames. Witnesses described a heavy cloud settling above the magazine complex, how the “strength of the flash” alone was enough to knock a man down, and how the lightning damaged the stone and brick of the building it hit.Footnote ³⁸ The Royal Society appointed a committee to investigate, made up of electrical experts William Henly, Timothy Lane, and Edward Nairne, as well as the Royal Society’s secretary, Joseph Planta.Footnote ³⁹ The investigative committee found that an iron tie connecting the rain gutter to the building was struck, but the electrical charge was not conducted through the gutters to the ground. Due to heavy rainfall, it conducted through water to a nearby lead plate and destroyed the intervening stonework.Footnote ⁴⁰ The damage to the building was minimal: the committee noted “it would scarce deserve notice” were it not for the fact that a nearby conductor “shewed no marks of its having been affected by the lightning.”Footnote ⁴¹ Ultimately, this committee took no issue with pointed conductors. They recommended creating a channel around the entire building and filling it with lead to more reliably connect all the parts of the existing system.Footnote ⁴²

Despite the findings of the committee, Wilson saw this moment as a vindication of his views, and once again published a dissenting opinion. He wrote that the buildings at Purfleet had never been struck by lightning before a pointed conductor was installed.Footnote ⁴³ He then argued that the only instance in which a pointed conductor could reduce the volume of electricity in a cloud was if that cloud happened to contain so little electricity that it would have already been “incapable of producing any fatal consequences.”Footnote ⁴⁴ His first point ignored the timeframe: Purfleet was not completed until 1773, and had enjoyed five years without a strike since having pointed conductors installed. His second point was a simple tautology. Wilson, however, had learned not to rely on the support of the scientific community. They had never been convinced by his arguments and would continue to support Franklin’s theories. Instead, he leaned on the personal connections he had made through his portraiture business—aristocrats who had the ear of the king, including the Marquess of Rockingham, the Delaval family, and the Duke of York.Footnote ⁴⁵ King George III was quick to weigh in against the treasonous Franklin and in favor of the loyal and well-connected Wilson. The king granted Wilson the use of the Pantheon ballroom to conduct further experiments to show the folly of pointed conductors.

For these experiments, Wilson built a model of the magazine at Purfleet, to which he could add pointed or blunted conductors. He then moved an electrically charged glass cylinder, meant to represent a cloud, toward the model and observed the effects of each type of conductor.Footnote ⁴⁶ Wilson did not use an electrometer, so the presence or absence of sparks, and the subjective measures of how loud and painful a given spark was, were his only gauges of electrical charge.Footnote ⁴⁷ When his model produced results that challenged his theory, he simply dismissed them, as in his fourteenth experiment when a pointed conductor failed to elicit a spark.Footnote ⁴⁸ Wilson wrote (without providing evidence) that this result would not hold “in other circumstances,” when the conductor and building were at full scale.Footnote ⁴⁹ He made no such qualification when a blunted conductor in the model was not struck under the same circumstances. Wilson’s results were inconsistent with each other and with his earlier assertions.Footnote ⁵⁰ A group of Franklin’s supporters led by the Earl of Stanhope countered many of Wilson’s conclusions by staging their own experiments at the Pantheon during the same period as Wilson; he deliberately avoided and ignored these experimental counterdemonstrations.Footnote ⁵¹

Wilson recorded fifty separate experiments, but the low quality of his work, and his failure to adhere to the scientific method, were apparent to others within the Royal Society and broader scientific community. For example, Charles Blagden, who was serving as a surgeon in the Revolutionary War but who later became secretary of the Royal Society, wrote that he had read Wilson’s “very confused pamphlet on his electrical experiments,” but believed they had been designed to appeal to the crowd rather than establish anything new in science.Footnote ⁵² The British physician Benjamin Vaughan described Wilson’s actions as a “contemptible … low intrigue.”Footnote ⁵³ The committee investigating the lightning strike acknowledged Wilson’s experiments, but still concluded that the solution to safeguard Purfleet was adding more pointed conductors.Footnote ⁵⁴ They concluded their recommendations with the definitive statement that “elevated rods are preferable to low conductors terminated in rounded ends, knobs, or balls of metal,” and that “the experiments and reasons, made and alledged [sic] to the contrary by Mr. Wilson, are inconclusive.”Footnote ⁵⁵ Even among loyal British subjects, the scientific consensus remained with Franklin and against Wilson. Despite the official opinion of the country’s leading experts on electricity, and public experiments demonstrating the flaws of Wilson’s interpretation, the king sided with Wilson against Franklin. George III ordered that pointed conductors be replaced with blunted ones on Kew Palace, and urged John Pringle to use his influence to support Wilson, despite the science.Footnote ⁵⁶ Pringle refused, resigned as president of the Royal Society and was removed as Royal Physician. He later claimed that he had retreated from public life due to ill health, but popular rumors held Wilson’s overtures to the king were the cause.Footnote ⁵⁷ Wilson himself would later admit the matter was more political than scientific:

Even Wilson recognized that king sided with him and his patrons at court on political grounds, and was not concerned with the experimental results, the underlying theories, or the consensus of the scientific community.

The controversy surrounding the Purfleet lightning strike demonstrates that the outcome of scientific debates depended on more than experimental evidence. Before 1777, Wilson had repeatedly challenged Franklin’s theory and conductor design, yet his objections failed to persuade the Royal Society because the experimental evidence did not support them. The American Revolution did not alter the scientific understanding of electricity, nor did it convince most natural philosophers that Wilson’s conductors were superior. Instead, it transformed the political context in which scientific authority operated. Franklin’s identification with the American revolutionary cause enabled his scientific opponents to recast a settled technical dispute as a question of loyalty and national interest, attracting the support of influential loyalist patrons, including the Delaval family, the Duke of York, and King George III.Footnote ⁵⁹ Although Franklin’s conductors remained the preferred design among electrical investigators in Britain, France, and North America, the controversy at Purfleet illustrates how political patronage could shape scientific institutions, public debate, and research priorities without overturning the underlying scientific consensus.

In time, Franklin’s scientific views became synonymous with his political ones. In 1783 Maximillien Robespierre defended pointed lightning conductors in court against the claim that they were a hazard.Footnote ⁶⁰ And in revolutionary America, Franklin commented:

In the decades prior to 1777, electrical conduction and the properties of lightning were regular features of experiment and study for the Royal Society. Each edition of Philosophical Transactions from 1770 to 1778 contained multiple articles on electrical experiments, the study of lightning, and the technology of lightning conductors. In the decade after 1777, very few studies related to electricity were published, and those that were published did not touch on the previously popular topics of electrical conduction, lightning protection, electrometry, or Franklinian theory even though these remained popular topics of study in North America and France during the same period. The outbreak of war between Britain and the American colonies overshadowed any scientific basis for valuing Franklin’s work and pursuing that area of academic inquiry. The king disapproved of Franklin’s role in the Revolution and his close connection to France. Wilson provided a political opportunity when he renewed his attacks on Franklinian science. The Purfleet controversy demonstrates that Britain’s response to the American Revolution extended beyond politics and war, transforming even ostensibly objective fields such as science into arenas in which questions of loyalty, patriotism, and political identity shaped authority more than experimental evidence did. This shows why the history of science must be considered in the context of the political and institutional forces that determine how science is valued, supported, and put into practice.