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.
Thunderstruck
If you are unfortunate enough to be hit by lightning, some of the current will flow over the surface of your body and some through your body, with the relative proportions depending on which path offers the least resistance. The former is less dangerous and it is likely that people who survive a strike mainly experience such a ‘flashover’. If you and your clothes are soaked by rain the water turns to steam, which can blow off your garments and burn your skin. Current that flows through the body can cause serious internal damage. Many people hit by lightning suffer cardiac arrest and require immediate cardiopulmonary resuscitation to avoid brain damage (people hit by lightning do not remain charged and can be safely touched). The respiratory centres in the brain may also be affected so that the person ceases to breathe. There are reports of people who were unable to breathe spontaneously for up to twenty minutes after a strike, despite cardiac function returning, so it is essential to continue artificial ventilation of victims who are apparently dead, as resuscitation is often successful. Neurological symptoms such as loss of consciousness, confusion, memory loss and partial paralysis, especially of the lower limbs, are very common. Other effects include hearing loss, blindness, sleep disorders and severe burns. The electric current can also stimulate muscle contraction, which is why people appear to jump or be blown across the room when struck. As all your muscles contract at once, they catapult you into the air.
The Frog’s Dancing Master
The dramatic effects of an electrical discharge, exemplified by electrostatic generators and lightning, led many eighteenth-century experimenters to seek to understand its physiological effects. Among them was the great Italian scientist Luigi Galvani, who was the first to discover ‘animal electricity’. Although Galvani had originally intended to enter the Church, his parents persuaded him to study medicine and by 1762 he was established as a professor of anatomy in his hometown of Bologna. Like many scientists of his day, he was interested in static electricity, and as early as 1780 he began to study its effects on muscle contraction. He worked with a small team that included his wife Lucia and his nephews Camillo and Aldini in a laboratory set up in his home.
Plate 1 of Galvani’s Commentarius showing several sets of dissected frogs’ legs. An electrostatic generator sits on the left of the table and a Leyden jar on the right. The small lace-cuffed hands pointing to the instruments, reminiscent of those used in the Monty Python films, were a common way to mark a point in the Renaissance.
On 26 January 1781, Galvani’s journal records, he serendipitously noticed that when his assistant touched the nerve that supplies the leg of a recently dead frog with a metal implement all the muscles in the legs twitched violently. However, this only happened at the precise moment that a spark was generated by the discharge of an electrical machine. Galvani repeated the experiment many times and in many different ways, but always got the same result. Consequently, he hypothesized that the electric spark was stimulating the muscle to contract. This led him to wonder if lightning could also cause the frog’s muscles to shorten. He tested this idea with the help of his nephew Camillo by attaching the nerve that supplies the frog’s leg muscle to a long wire that was connected to a metal spike that he placed at the top of his house, pointing towards the sky. As he had predicted, he found that the frog’s legs twitched wildly when the lightning flashed during an electrical storm.
Being a careful scientist, Galvani repeated the experiment on a calm day, as a control. This time he suspended the frog’s legs from the iron railings of his balcony by brass hooks that pierced the
spinal cord. At first, nothing happened. Getting impatient, Galvani began to fiddle with the frog’s legs. To his surprise, he noticed they then began to display frequent spontaneous and irregular movements, none of which depended on the variations of the weather, but which occurred when the hooks were pressed against the railing.
Galvani interpreted this result to indicate that animal cells are not only stimulated by electricity – they can actually produce their own. This electrical (self)-stimulation, he surmised, produced contraction of the muscle. In 1791 he published his discoveries in a pamphlet entitled De viribus electricitatis in motu musculari commentarius (‘A commentary on the effects of electricity on the motion of muscles’) in which he contended that animal electricity was different in kind from that produced by lightning or an electrostatic generator, and he argued that ‘the electricity was inherent in the animal itself’. Galvani had a few copies of his article published at his own expense and sent them to his fellow scientists, including his friend and countryman, Alessandro Volta, who was professor of physics at the University of Pavia.
At first his colleagues accepted Galvani’s ideas with cautious enthusiasm, repeating his experiments and obtaining the same results. As a consequence, the supply of live frogs diminished precipitously and a year after Galvani’s publication Eusebio Valli was complaining to a colleague, ‘Sir, I want frogs. You must find them. I will never pardon you, Sir, if you fail to do so. I am without ceremonies, Your most humble servant, Valli’.
Volta’s experiments caused him to revise his initial conclusion that Galvani was correct, and argue instead that the muscle twitches Galvani had observed in the absence of extrinsic electrical stimulation were not due to an innate animal electricity. Rather, he deduced (correctly) that they were induced by an electric current flowing between two dissimilar metals – the iron railing of the balcony and the brass hooks which Galvani had attached to the nerve supplying the frog’s leg. This initiated a heated controversy between the two scientists about whether the origin of the stimulus was biological or physical.
While Galvani acknowledged Volta’s argument, he remained convinced that animal electricity was a real phenomenon. Crucially, he showed that putting the nerve in contact with the muscle was enough to cause a spasm – no metal at all was needed. We now know that this experiment worked because the injured tissue generates an electric current that is able to stimulate the muscle, although Galvani did not realize this. Unfortunately, he published this experiment anonymously, which somewhat diminished the force of his argument.
Power to the People
The fact that contact between the nerve and muscle was sufficient to cause contraction was a triumph for galvanism and a setback for Volta. But he was not defeated and continued to explore the idea that contact between dissimilar metals was involved. Believing that electricity was not of animal origin, he decided to dispense with the frog entirely. He built a stack of alternating silver and zinc discs, separated by cardboard soaked in salt water, and demonstrated that an electric current flowed when the top and bottom of the pile were connected. He had invented the first electric battery. Indeed, he got an electric shock by touching one hand to the top and the other to the bottom of the pile. Volta also drew attention to the striking resemblance of his apparatus to the electric organs of electric eels and rays, fish well known for their ability to give humans a substantial electric shock. The electric organs of these fish consist of stacks of cells separated by conducting fluid, analogous to Volta’s pile of silver and zinc discs.
The shock produced by Volta’s early battery was feebler than that of a Leyden jar, but it had a singular advantage: it was produced indefinitely and did not need to be charged in advance from an electrostatic generator. Larger currents – and thus bigger shocks – could be produced by increasing the height of the pile of discs. Volta described his invention in a letter to the Royal Society of London in 1800 entitled ‘On the electricity excited by the mere contact of conducting substances of different kinds’. Written in French by an Italian scientist to an English institution, it demonstrates that even in 1800 science was an international activity. Volta later presented one of his own voltaic piles to the Royal Institution in London where it can still be seen today.
Clash of the Titans
The disagreement between Galvani and Volta over the interpretation of the frog experiments is sometimes portrayed as a scientific feud, with Galvani being the loser; and the invention of the battery was seen a triumph of Volta over Galvani, and of physics over biology. But Galvani was not completely wrong, because his idea that animals produce electrical signals in their nerves and muscle fibres turned out to be correct. Unfortunately, the fact that Volta’s ideas took precedence probably set back the science of animal electricity for some time.
Although the issue divided the scientific community, and their supporters fought about the matter, the dispute between Volta and Galvani themselves was not acrimonious. Volta wrote of Galvani’s work that it contained ‘one of the most beautiful and most surprising discoveries’ and he is credited with inventing the term ‘galvanism’. He even communicated Galvani’s findings to the Royal Society of London, writing ‘an account of some discoveries made by Mr Galvani, of Bologna; with experiments and observations on them’. Interestingly, in his very first sentence he refers to the subject of his letter as discoveries and researches on ‘L’Electricité Animale’, although he goes on to conclude that it does not exist.
Perhaps some of the reason that Galvani’s ideas fell into abeyance is that he was a less effective champion than his rival. Galvani was a rather retiring individual. He only published his work in 1791, at least ten years after his initial experiments, and he did so (in Latin) in the transactions of the Bolognese Istituto delle Scienze, which were not widely available. He compounded the problem by being averse to travel, a poor correspondent, failing to publish some of his experiments altogether and generally communicating his findings only to his immediate circle. Political problems also hindered Galvani’s work. In 1794 Napoleon conquered Bologna and two years later Galvani was forced to resign his professorship because he refused to take the loyal oath to the French Cisalpine Republic demanded by the university as it contravened his political and religious principles. He fled to the home of his brother Giacomo, where he broke down in despair. His friends obtained an exemption from the oath for him, on account of his scientific accomplishments, but tragically he died before it could be implemented. He was only sixty-one.
Volta had a very different temperament and life. He was a charismatic and dynamic speaker and a prolific (occasionally arrogant) author who published in several languages, promoted his work widely and willingly accepted the new regime. Volta became very well known and was fêted throughout Europe. In 1801, he was invited to Paris, where he was presented with a gold medal and gave three lecture demonstrations on his findings, all of which were attended by Napoleon. Volta collected many other prizes and distinctions, being appointed to the Legion of Honour by Napoleon in 1805 and later being made an Italian senator and subsequently a count. The unit of electrical potential was also named the ‘volt’ in his honour. Far more politically astute than Galvani, Volta continued to find favour even after Napoleon fell and power shifted to Austria.
The ‘Mad’ Scientists
Galvani’s experiments generated considerable excitement. All across Europe, scientists and laymen alike tried to reproduce his findings, not only on recently dead frogs but also on other dead animals. Galvani’s flamboyant nephew, Giovanni Aldini, brought electricity to public attention in a particularly sensational way. An extraordinary synthesis of scientist and showman, his (in)famous public demonstrations may have inspired Mary Shelley’s novel Frankenstein, for not content with merely applying electric shocks to frogs’ legs, Aldini used the bodies of recently executed criminals. Ironically, given his fierce antagonism to Volta, he had to rely on a voltaic pile to generate the necessary shock.
Illustration from Aldini’s treat
ise on his experiments on the decapitated cadavers of criminals, Essai théorique et éxperimental sur le galvanisme. The tall, pencil-like structure is a voltaic pile (a primitive battery), which is used to generate an electric current. The current is applied to the corpse via a curved metal rod attached to an insulating glass handle that is held by the experimenter to prevent him getting a shock.
Aldini’s notes record that in 1802, ‘The first of the decapitated criminals was transported to the room I had chosen, close to the place where the execution was carried out. The head was first subjected to galvanic action using a stack of a hundred pieces of silver and zinc. A metal wire was placed inside each of the two ears, which had been moistened with salt water. The other end of the wire was connected to either the top or the bottom of the pile. I initially observed strong contractions in all the muscles of the face, which were contorted so irregularly that they imitated the most hideous grimaces. The action of the eyelids was particularly marked, though less striking in the human head than in that of an ox.’
His most notorious demonstration took place in London on 17 January 1803 when he electrified the corpse of the murderer Thomas Forster. Immediately after his execution (by hanging), the body of the malefactor was conveyed to the Royal College of Surgeons where a large audience awaited. Aldini took a pair of conducting rods, each connected at one end to a voltaic pile, and applied the other end of the first one to the corpse’s mouth and that of the second to the ear, whereupon ‘the jaw began to quiver, the adjoining muscles were horribly contorted, and the left eye actually opened’. When the rods were applied to the dissected thumb muscles they ‘induced a forcible effort to clench the hand’. In another experiment, violent convulsions were produced in all the muscles of the arm. The highlight of the demonstration came when rods were applied to the ear and rectum, which ‘excited in the muscles contractions much stronger [. . .] so much increased as almost to give an appearance of re-animation’.
The Spark of Life: Electricity in the Human Body Page 3
