The Acts of God Committee

Lightning-proofing St Paul’s and the Purfleet magazines.

It’s a well-attested fact that when a person embarks on a historical research project, however apparently specific, they start to see it everywhere. My commute to the Royal Society Library takes me under the Thames and past Purfleet, site of the Board of Ordnance’s gunpowder magazines after they were moved from Greenwich in 1765. You can’t see the one surviving magazine building from the train – the lines of sight aren’t quite right – but Purfleet is one of a couple of places on that route with a connection to the history of the Philosophical Transactions of the Royal Society.

In August 1772 the Royal Society was asked by the Board of Ordnance to put together a committee to consult on the best way of securing the new magazines at Purfleet against lightning strikes. Their caution was well-advised; there had been enough recent instances of fires started by lightning strikes, and an explosion in a firework shop in the City of London in 1715 had started a fire which one contemporary estimated to have caused half a million pounds’ worth of damage and killed 60 people before it was stopped – quite a lot more than the official death toll from the Great Fire of 1666. The danger of storing powder in populated areas was surely one of the factors in moving the magazines to Purfleet in the first place.


An example of the effects of a lightning strike: damage to the walls and rafters of Heckingham Workhouse, Norfolk, 1782. Watercolour subsequently published in Phil Trans 72 (1), 1782, pp.355-378.


The Society already acted for the Ordnance Board in a supervisory capacity; they carried out an annual inspection of the Royal Observatory at Greenwich and made recommendations about its fabric, instrumentation, and staffing requirements, as well as supervising the annual publication of the Astronomer Royal’s observations. With a view to avoiding regaling the residents of Gravesend with an inadvertent firework display, the Society asked James Robertson, William Watson, Benjamin Wilson, Henry Cavendish, and Benjamin Franklin – that Benjamin Franklin – to inspect the Purfleet site and make recommendations. This they did, advising the installation of lightning conductors and suggesting specifications for them. Their recommendations were published in Volume 63 of the Philosophical Transactions.

In fact this was the Royal Society’s second committee on the matter of lightning conductors. Some readers may remember a dramatic news photo of lightning striking the Vatican during the last papal conclave, jokingly interpreted in some quarters as a mark of divine displeasure at Benedict XVI’s resignation from the papacy. Back in 1769, the Dean and Chapter of St Paul’s Cathedral, legitimately concerned about the danger to the handsome fabric of Wren’s building, displayed a more practical and less providential attitude, and called the Society in to advise, perhaps remembering the damage caused to the old building by two separate lightning strikes, as well as a more recent one at St Bride’s nearby that had blown an eight-foot section off its beautiful tiered spire. The results of this consultation were also published, in Phil Trans 59. The Society then revisited St Paul’s in 1773, a week after it was actually struck by lightning, and while viewing the damage gloomily noted that their instructions hadn’t been followed precisely – the conductors weren’t continuous and had been allowed to rust, which severely diminished their effectiveness, as Franklin and others had pointed out.

A little unusually, however, one member of the committee publicly dissented from the recommendations. Benjamin Wilson was so concerned about the merits of pointed as opposed to blunt lightning conductors – he thought that a broader surface area at the top of the conductor stood a better chance of surviving a lightning strike undamaged – that he put his objections in writing, and published them in the same volume of the journal. The committee saw no reason to change their recommendation, however, and said as much in the fairly bland note they printed in reply to Wilson.

The conductors at Purfleet were put to the test by a lightning strike in 1778, which did some damage to the brickwork and the roof, renewing the anxiety of the Board of Ordnance and spurring Wilson on to a series of experiments to model the effects of a lightning strike indoors, at the Pantheon on Oxford Street; these were reported in the Phil Trans for 1778, and the apparatus he used is illustrated below. Wilson continued to insist that broad-tipped lightning conductors would work better; the Society continued to stick to its original position, and to insist in print that the Purfleet conductors had worked perfectly adequately.


‘A view of the Apparatus and part of the Great Cylinder in the Pantheon’, by Benjamin Wilson.
From ‘Sundry papers relative to an accident from lightning at Purfleet, May 15, 1777’, Phil Trans 68, 1778, pp.232-317


The Royal Society had supplied advisory committees of this kind before, and would continue to do so through the nineteenth century and beyond. But it’s a little unusual to see the results being published; these articles in the Phil Trans show the Society engaging positively with the idea that science, or natural knowledge, should be deployed for the public good, an idea which had been part of its brief since its inception but which it had sometimes struggled to live up to. It’s even more unusual to see them publishing a dissenting opinion. Resistance to controversy became a very strongly entrenched aspect of the Society’s public face in the eighteenth century, and after the Society took over the publication of Phil Trans in 1752 – it had previously been the private venture of the Society’s Secretary – some of that culture seems to have spread to the Phil Trans as well. The selection of papers for publication was taken by secret ballot and without discussion, just as the Society’s meetings had been transformed from the lively discussions of its early years into a respectful forum in which papers were listened to in silence.

The lightning-proofing committees represent two facets of the Society at this time; it was becoming bolder in its ventures into the public arena, yet oddly restrictive of free debate in its meetings and publications. Joseph Banks, who became President in 1778 and served until 1820, hugely increased the Society’s advisory roles in government affairs, but he was also known for his rather autocratic leadership. It would be this, in the early nineteenth century, which led to increasing calls for reform of the Society, from within and without – calls that would have substantial, if gradual, effects on the Society’s membership, its practices of discussion, and the Phil Trans themselves.