The Spark of Life: Electricity in the Human Body (2 page)

1

The Age of Wonder

I am attacked by two very opposite sects – the scientists and the know-nothings. Both laugh at me – calling me ‘the Frog’s Dancing-Master’, but I know that I have discovered one of the greatest Forces in Nature.

Luigi Galvani
¹

‘It was on a dreary night of November, that I beheld the accomplishment of my toils. With an anxiety that almost amounted to agony, I collected the instruments of life around me, that I might infuse a spark of being into the lifeless thing that lay at my feet. It was already one in the morning; the rain pattered dismally against the panes, and my candle was nearly burnt out, when, by the glimmer of the half-extinguished light, I saw the dull yellow eye of the creature open; it breathed hard, and a convulsive motion agitated its limbs.’ Thus did Victor Frankenstein, in Mary Shelley’s great gothic novel
Frankenstein
, written in 1818, record his creation of a monstrous being.

It is widely believed that electricity, in the form of a lightning bolt, was used to waken Frankenstein’s creature to life. But this is a misconception that probably originates with the famous 1931 film in which Boris Karloff played the monster. Shelley herself was far more circumspect and refers only to the ‘instruments of life’. Nevertheless, the novel leads us to infer that electricity was used to instill the monster with ‘a spark of being’, for Frankenstein gives a dramatic description of a lightning strike he witnessed as a young man that blasted an ancient oak tree to smithereens; and on inquiring about the nature of lightning from his father, he was informed it was ‘Electricity’. Shelley also uses her preface to make a marriage of physiology and electricity – ‘perhaps a corpse would be reanimated; galvanism had given a token of such things’.

Indeed, both Mary and her lover Percy Bysshe Shelley took a keen interest in the emerging science of electricity and its effects on the human body. Percy was a particular enthusiast having experimented with electricity at Eton, at Oxford and even at home – his sister recounts how she was terrified of being ‘placed hand-in-hand round the nursery table to be electrified’. Percy was eventually sent down from Oxford for his atheist views and in 1810, during the winter vacation before his last term, he wrote to his tutor that he supposed man to be ‘a mass of electrified clay possessing the power to confine, fetter and deteriorate the omnipresent intelligence of the universe’. Over 200 years later, ‘electrified clay’ remains a fair description of the human brain.

Although we may scoff at the idea that electricity could animate a lifeless creature and know that a lightning strike is often lethal, even today we are not immune from the idea that electricity is the spark of life. A late-night arts programme on British television (
The South Bank Show
) is introduced by a modified version of Michelangelo’s famous painting of God creating Adam, in which an electric spark leaps from God’s outstretched finger. Nor is the idea entirely fanciful for, like almost all organisms, humans are electrical machines. As this chapter shows, the development of our knowledge of ‘the body electric’ is intimately entwined with our understanding of electricity itself.

The Dawn of Understanding

On a dry wintry day you may receive a sharp electric shock when you open the car door or grab a metal doorknob, and find that sparks fly and crackle when you pull off a nylon shirt. Petticoats that cling to your legs, clothes fresh from the tumble dryer that stick together, hair that stands on end when you remove your hat, an electric jolt when you kiss someone, the faint battle-rattle of electric sparks, like ‘tiny ghosts shooting’, as you comb your hair – all these phenomena happen because static electricity builds up on our bodies. In humid atmospheres the charge dissipates quickly, but under dry conditions it can build up to thousands of volts. Close proximity to metal, however, or even another person, will cause it to discharge. Direct contact is unnecessary, as the electricity will jump the gap, generating a spark in the process. The ‘electricity’ between two people, that special spark, may be more than just lovers’ talk.

The science of static electricity starts with the ancient Greeks’ fascination with amber. It is from their word for amber,
electrum
, which derives from
elector
, meaning ‘the shining one’, that we get the word electron, and hence electricity. Because it was usually found washed up on the seashore, amber’s origin was always considered mysterious. The historian Demostratus supposed it the crystallized urine of lynxes. Ovid tells a different story. He relates how Phaethon drove Apollo’s chariot (the Sun) too close to the Earth and was struck down by Zeus to prevent a catastrophe. His grief-stricken sisters were transformed into poplar trees and shed golden tears of amber that fell into the River Eridanus in which Phaethon drowned.

Of course, we now know that amber is the petrified resin of extinct pine trees and are familiar with it as jewellery, or as the medium in which prehistoric insects have been encapsulated and perfectly preserved. But amber has another interesting and curious property. When rubbed with wool it generates static electricity, causing it to attract light, dry objects like small bits of tissue paper, feathers, specks of wheat chaff, and even your hair; this may be why Syrian women, who used decorative amber weights on the end of their spindles when spinning wool, called it the ‘clutcher’. Thales of Miletus is credited with being the first to note the attractive properties of amber, in the fifth century
BC
, although it is hard to be certain, as his findings were only passed down orally until later philosophers, such as Theophrastus, wrote them down.

Amber generates a static charge because it attracts electrons from the atoms of the wool, becoming negatively charged in the process and leaving the wool positively charged. The charge is transferred by close contact between the amber and wool – the friction produced by rubbing is not involved, it is simply that rubbing greatly increases the area of contact between the two surfaces. Because opposite charges attract, any material that is naturally positively charged will leap towards the negatively charged amber. Conversely, as similar charges oppose one another, charging up your hair will cause each strand to repel its neighbours as much as possible, producing flyaway hair that stands on end like that of Shock-headed Peter in the German children’s picture book. Parenthetically, there is nothing static about ‘static’ electricity. The term refers only to the fact that the positive and negative electric charges are physically separated. As soon as a positively charged material comes close enough to a negatively charged one, current will flow from one to the other – as visibly demonstrated by the leap of an electric spark.

It was William Gilbert, physician to Queen Elizabeth I, who first invented a sensitive instrument for measuring static electricity (an early electroscope). He used it to compile a long list of materials that could be electrified by rubbing. He also distinguished the attractive power of amber from that of magnets, arguing that two different phenomena are involved. Gilbert was a true scientist, for he advocated that you should not believe what you read, but instead try the experiment for yourself. He wrote, ‘Our own age has produced many books about hidden, abstruse, and occult causes and wonders, in all of which amber and jet are set forth as enticing chaff; but they treat the subject in words alone, without finding any reasons or proofs from experiments, their very statements obscuring the thing in a greater fog’. Hence, he concluded, ‘all their philosophy bears no fruit’. His words were prescient – present-day scientists make similar complaints about the advocates of astrology and alternative medicine.

Great Balls of Fire

The first machine capable of generating static electricity was invented by the German Otto von Guericke around 1663. It consisted of a giant ball of brimstone, about the size of a child’s head, with a wooden rod through its centre. The rod rested in a cradle, enabling the ball to be rotated on its axis by cranking the handle. When a dry hand or a pad of material was held against the whirling ball, static electricity was generated. It is unlikely that von Guericke appreciated that his machine produced electricity, in the modern sense of the word, but he did observe that the globe attracted feathers and other light material, and that once they had first touched the ball, the feathers were repelled and could be chased around the room by lifting the ball from its rod. Careful manipulation even allowed him to balance the feather on another object, such as a colleague’s nose.

Frontispiece to
Novi profectus in historia electricitatis, post obitum auctoris
, by Christian August Hausen (1743), depicting the ‘flying boy’ experiment of Stephen Gray. Von Guericke’s ball can be seen on the right. The small boy on the left appears to be standing on an insulating drum, so he will not feel a shock when he touches the flying boy. However, when the gentleman does so, sparks will fly as the current leaps between their fingers and flows through his body to the ground.

One of the most famous uses of von Guericke’s machine was the ‘flying boy’ experiment carried out by Stephen Gray in 1730, for which he was awarded the first Copley medal of the Royal Society of London. The child was suspended in mid-air by insulating cords of silk and then charged up by holding his feet against a rotating sulphur ball. Tissue paper, chaff and other light objects were attracted to his hands, and sparks flew from them when he was discharged.

Large balls of sulphur are not easy to come by, so later electrostatic generators incorporated a circular plate (or spherical globe) of glass that rotated against a fixed cloth; one that was 50 inches in diameter was made for the Emperor Napoleon. The modern equivalent is the Van de Graaf generator, which can produce millions of volts and is well known for its use in spectacular ‘hair-raising’ demonstrations.

A Jarring Shock

There was no way to store static electricity until the invention of the Leyden jar in October 1745 by a German cleric, Ewald Jürgen von Kleist. Just a few months later the Dutch scientist Pieter van Musschenbroek reported a similar, independent, discovery to the Paris Academy of Sciences. His letter was translated by Jean-Antoine Nollet, the Abbot of the Grand Convent of the Carthusians in Paris, who named the device the Leyden jar, after
Leiden
, the Netherlands city in which Musschenbroek worked.

The Leyden jar resembles an empty glass jam jar coated inside and out with a thin layer of metal foil that extends about two-thirds of the way up its sides. A brass rod is inserted through an insulating cork stopper into the neck of the jar and connected to the inner metal foil by a chain. If the outer layer of foil is grounded, the inside can be charged up by connecting the rod to a static electricity generator. This happens because the glass wall of the jar acts as an insulator and prevents the charge from flowing to the outer layer of foil, so that a very high charge difference can be built up between the two metal layers. The device is discharged by connecting the inner and outer layers of foil, either with two wires – which generates impressive electric sparks as the wires approach one another – or, more inadvisably, with one’s hands.

The charge stored in a Leyden jar can be considerable – and extremely dangerous – as van Musschenbroek discovered. He wrote, ‘my right hand was struck with such force that my whole body quivered just like someone hit by lightning [. . .] the arm and the entire body are affected so terribly I can’t describe it. I thought I was done for.’ He also said that he would not repeat the experiment if offered the whole kingdom of France and cautioned others not to try it. But of course they did, with predictable effects. Some had convulsions or were temporarily paralysed. One German professor who got a severe shock and a bloody nose refused to test it on himself again and instead next tried it on his wife!

The effects were clearly well known to Jules Verne, who described a fantastical device in
Twenty Thousand Leagues under the Sea
. In the novel, Captain Nemo explains to Monsieur Arronax that his underwater rifle fires glass capsules, which are ‘exactly like miniature Leyden jars, into which the electricity has been forced at a very high voltage. They discharge at the slightest impact, and however powerful the animal, it falls down dead’. His account contains some artistic licence, but shows how dangerous the Leyden jar was considered to be.

The severity of the shock from a Leyden jar surprised the experimenters because it was much stronger than that of a single spark produced by an electrostatic generator. This was because the jar could accumulate and store the charge flowing in many sparks, which would then be released all at once. Initially, it was believed that electricity was a fluid, so it seemed natural to use bottles and jars to store it in, but it was later appreciated that this was not the case and today the Leyden jar has been replaced by the capacitor. This operates on the same principle. It consists of two parallel metal plates separated by a thin layer of a non-conductive material such as mica, glass or air. The amount of charge a capacitor can store is determined by the area of the plates and the distance between them, and it can be considerable. The first atom smasher, built in the 1930s at Cambridge University by John Cockcroft and Ernest Walton, used banks of capacitors to generate and store up to almost a million volts.