The Spark of Life: Electricity in the Human Body (3 page)

Nine Lords a-Leaping

Another early demonstration of the effects of electricity on the human body was that conducted by the Abbé Nollet. In 1746, he ordered 200 of his monks to form up in a large circle almost a mile in circumference, holding long iron rods between their hands. Once they were all in position, the Abbé surreptitiously connected the two ends of the circle to a Leyden jar. The results were spectacular because the discharge of the jar sent a shock wave through the circle that caused all the monks to jump in turn, thereby demonstrating that electricity travels extremely fast. The French Academician Le Monnier wrote, ‘it is singular to see the multitude of different gestures and to hear the instantaneous exclamations of those surprised by the shock’. Hearing of the performance, King Louis XV demanded a rerun at Versailles and a company of 180 soldiers holding hands leapt simultaneously. Adam Walker, a popular British electrical performer in the late eighteenth century, went even further, boasting, ‘I have electrified two regiments of soldiers, consisting of eighteen hundred men.’

Such experiments created a sensation. Public demonstrations of electrical phenomena rapidly became the rage, and itinerant lecturers roamed the country. Their aim was more spectacle than science, and performances were generally advertised for their entertainment qualities as much as their educational content. One of the most famous presenters was Benjamin Martin, a consummate entertainer who introduced a season of lectures at Bath in 1746 in which he used a Leyden jar to produce luminous discharges, and ‘wonderful Streams of Purple Fire’, which looked both beautiful and exotic in a darkened room. Like the Abbé Nollet, he also excited his audience by getting them to join hands and then applying an electric shock, which was not ‘so violent and dangerous as they have been represented, tho’ they are nearly as great as any Person (especially the
Men
) care to endure’. One letter of the time commented that these public spectacles were ‘the universal topic of discourse. The fine ladies forget their cards and scandal to talk of the effects of electricity’.

On other occasions members of the public were invited to be charged up with static electricity and then ignite brandy or ether with sparks from their fingertips. Ladies donned glass slippers to insulate them from the ground and were electrified so that when their gentlemen friends approached with puckered lips outstretched, sparks flew between their lips. The electrified Venus, as she was known, gave stinging kisses. Electric toys abounded. Hidden words were magically revealed using ‘fulminating boards’ in which sparks jumped between small gaps in a conducting track, paper dancers were animated by the attractive and repulsive forces of static electricity, thunder houses were used to demonstrate the effects of lightning on buildings. Even more dramatic were the pistols and toy cannons that were fired using the heat of an electric spark.

Many of these early demonstrations – and their protagonists – were viewed with suspicion because it was believed that electricity was a manifestation of the force of life and to tamper with it was blasphemy. For others it was a form of fire, which is why Mary Shelley subtitled her book
The Modern Prometheus
, after Prometheus, the mythical Greek who stole fire from the gods to give to mortals.
²
At best, electricity was considered simply a novelty, an entertaining curiosity of no practical value. At which point Benjamin Franklin entered the scene and changed that view forever. In his hands, electricity left the salon and become the province of science.

Snatching Lightning from the Sky
³

Franklin is widely believed to have been the first to show that lightning is a form of electricity. His most famous experiment was carried out in June 1752, when he flew a kite as a thunderstorm approached to prove that lightning is a stream of electrified air. He connected a short, stiff, pointed wire to the top of the kite, tied a metal key to the end of the kite string and attached the key to a silk ribbon, so insulating it from the ground. Whenever a thundercloud passed overhead, Franklin observed that the loose fibres of the hemp string would stand on end, suggesting that the twine became electrified. He even noted that a stream of sparks would leap from the key to his fingers, and that it was possible to charge a Leyden jar by touching it to the key. Franklin was fortunate not to have been struck by lightning, as this was a very dangerous experiment.

But Franklin was not the first to demonstrate that lightning is an electrical discharge. That accolade goes to a Frenchman, Thomas-François Dalibard. In May of the same year, Dalibard erected an inch-thick, 40-foot-high iron pole, carefully insulating it from the ground by standing it on a plank balanced on three wine bottles and securing it with silken ropes. Sparks could be drawn from the rod with a Leyden jar when lightning was in the area. As Dalibard acknowledged, his experiment was inspired by Franklin’s paper describing his ‘Experiments and Observations’ on electricity, in which the American conjectured that such a pointed rod should draw lightning from the cloud and advised on how harm to the experimenter might be avoided. Dalibard’s demonstration created a sensation throughout Europe and was rapidly repeated by many others. Alas, not all were as careful or as lucky as Dalibard. The Swedish scientist Georg Wilhelm Richman was electrocuted a year later while experimenting with lightning conductors; his death is commemorated in a rather flowery poem by Erasmus Darwin (uncle of the more famous Charles), whose narrator –

          eyed with fond amaze

          The silver streams, and watch’d the sapphire blaze;

          Then burst the steel, the dart electric sped

          And the bold sage lay number’d with the dead!

The Franklin Memorial in Philadelphia is inscribed with some of the statesman-scientist’s words of wisdom: ‘If you would not be forgotten as soon as you are dead and rotten, either write things worth reading or do things worth the writing.’ Franklin, of course, did both. One of his lasting legacies is the lightning conductor. Being aware that lightning was simply a form of electricity, and knowing that lightning strikes the tallest objects, he advised fixing on the ‘highest Parts of those Edifices upright Rods of Iron, made as sharp as a Needle and gilt to prevent Rusting, and from the Foot of those Rods a Wire down the outside of the Building into the Ground’. These pointed rods, he surmised, would conduct the strike safely to the ground so the building would not be damaged – or as he more poetically phrased it, ‘secure us from that most sudden and terrible Mischief!’

Initially support for Franklin’s idea was not universal. Some objected that it would attract lightning to the house, thereby increasing the danger. Others considered it presumptuous as it interfered with the will of God; in Franklin’s time many people believed lightning was God’s punishment upon the sinful. Franklin countered that lightning was ‘no more supernatural than the Rain, Hail or Sunshine of Heaven, against the Inconveniences of which we guard by Roofs and Shades without Scruple’. His argument, and the manifest value of his invention, soon led to the installation of lightning conductors on most gunpowder stores, and even cathedrals.

But in England there were problems. An acrimonious debate broke out between those who supported Franklin’s idea of a pointed tip to a lightning conductor and those who preferred a round knob, on the grounds that a sharpened point was dangerously effective and attracted the lightning to it. The latter idea was championed by Benjamin Wilson. He campaigned vigorously against Franklin and he had powerful friends. Matters came to a head in 1777, when the gunpowder magazine administered by the Ordnance Board at Purfleet on the Thames was struck by lightning, and a few bricks were dislodged. The pointed rods previously installed on the advice of Franklin and his colleagues had seemingly not protected the building. Wilson took full advantage of the disaster, producing a spectacular electrical extravaganza at the Pantheon designed to prove that high spikes were dangerous and low blunted knobs were to be preferred. It was performed in the presence of King George III and many prominent ministers, who were impressed by his arguments. The fact that this took place at the time of the American War of Independence added a further charge to the issue. What had begun as a scientific spat quickly escalated into a major feud between the British knob and the American spike factions, with Wilson proclaiming that it was Britain’s patriotic duty to dismiss the invention of the enemy. Franklin’s friends countered with equally damaging political attacks. The Royal Society waded in, carried out a series of experiments and concluded that Franklin was correct. King George, however, sided with Wilson, ordering pointed spikes to be removed from all royal palaces and Ordnance buildings and demanding the Society reverse its conclusions. But John Pringle, the President of the Society, declined to do so, memorably stating that ‘duty as well as inclination would always induce him to execute his Majesty’s wishes to the utmost of his power; but “Sire [. . .] I cannot reverse the laws and operations of nature”’. The king promptly suggested he had better resign. Shortly after, a witty friend of Franklin’s lampooned the king in the following epigram:

          While you, great George, for knowledge hunt,

          And sharp conductors change for blunt,

          The nation’s out of joint:

          Franklin a wiser course pursues,

          And all your thunder useless views

          By keeping to the point.

It was not all plain sailing in France either. Monsieur de Vissery of Arras was ordered to remove a lightning rod he had attached to the chimney of his house. He appealed. By the time the case reached the provincial court of last appeal in 1783, after three years of argument, the case had become the talk of Paris and a political lightning rod. An obscure young lawyer called Maximilien Robespierre made his name by defending science against superstition and winning the case, arguing that while theory required experts to interpret it, the facts did not. Ten years later, the National Convention, led by Robespierre, used a similar argument to get rid of government experts and all national academies and literary societies. Robespierre is best known for instituting the Reign of Terror during which many French aristocrats were guillotined. It is possible that without his successful defence of Monsieur de Vissery and his lightning conductor, Robespierre might not have moved to Paris and the course of French history might have been very different.

Today, almost all tall buildings sport lightning rods similar to those advocated by Franklin, that lead the electric current safely to the ground and spare the building. Large structures may have several of them. St Paul’s Cathedral in London, for example, has them spaced at regular intervals around the roof. And they are essential: the Empire State Building is regularly hit during a lightning storm, demonstrating that the axiom ‘lightning never strikes twice in the same place’ is a dangerous fallacy.

Franklin advised that it was not wise to shelter under an isolated tree in a storm, as it was likely to attract a lightning strike. He also noted that wet clothing provides a low resistance path to ground (outside the body), so that the current flash preferentially runs over the surface of the body rather than through it, and he concluded that this was why a ‘wet Rat can not be kill’d by the exploding Electric Bottle when a dry Rat may’. His idea may explain why one young man hit by a lightning bolt survived unscathed, for he was wearing an oilskin (rain slicker) that was soaking wet from a torrential rainstorm. His father witnessed the lightning strike from the safety of his pick-up truck and rushed his son to hospital; but he was discharged an hour later with no ill effects. Most people are not so lucky, and lightning strikes kill and maim hundreds of people every year.

Bolts from the Blue

Lightning is bred in cumulonimbus, those towering anvil-shaped clouds with billowing sides and flat bottoms that form when warm moist air rises to a height at which it is cold enough to freeze water. In such thunderclouds, ice particles and water droplets are continually colliding as air movements swirl them about. Tiny ice crystals become positively charged and are tossed to the top of the cloud, whereas bulkier chunks of ice and slush, the size of small hailstones, become negatively charged and sink to the bottom. This creates a charge separation, with upper layers of cloud having a positive charge and the lower ones a negative one. The voltage difference between the negatively charged lower layers of the cloud and the ground can reach as much as 100 million volts. At some point this difference is so great that it exceeds the insulating capacity of the air, and the current arcs to ground in a lightning flash. It lasts only a fraction of a second. There is also a rare form of lightning in which the bolt issues from the top of the cloud. Such ‘positive lightning’ is highly dangerous, as it can strike ground many miles from the cloud, without warning, on a sunny day – a veritable bolt from the blue.

A lightning bolt can reach speeds of 60,000 metres a second and temperatures of 30,000°C, five times hotter than the surface of the Sun. It averages three miles long, but is only about a centimetre wide. Each flash is actually made up of several individual discharges that occur too fast for the eye to distinguish them fully, which explains why lightning appears to flicker. A single strike unleashes as much energy as a ton of TNT and the intense heat induces an explosive expansion of the air at speeds that break the sound barrier, which is heard as a thunderclap. Although thunder and lightning are generated simultaneously, light travels much faster than sound; 186,000 miles a second as compared to a mere 0.2 miles a second. Thus you see the flash first and hear the thunder some time later, depending how far away the storm is.