We take electricity for granted. But when the lights go out and the tube trains stop - as has happened in London, Italy and parts of the US in the past two months - we suddenly take notice. At first, it was little more than a novelty. Then it became a welcome convenience. Now, within less than a century, electricity has effectively taken over our lives.

Electricity isn’t “stuff” in the way that gas is. Neither was it invented by anybody. Dinosaurs, presumably, were occasionally struck by the powerful electrical discharges seen as lightning, but we have a problem in defining it. Part of the problem is the language. The words - current, flow, resistance, charge - come loaded with everyday meanings that may be unhelpful. The very word “electricity” can mean different and sometimes contradictory things.

Electricity and electrical energy aren’t the same thing. Electricity is embodied in sub-atomic particles (the electrons and protons which carry electric charge). The flow of electrical energy is often mistakenly envisaged as a flow of electrons along a conductor (usually a wire). In fact, electrons don’t run along wires, but they do move a tiny bit. In that little bit of movement, electrons transfer electrical energy into the cables, wires and earth that form the circuit from power station to your home and back again. The electrical energy is then converted into other forms of energy - heat, light, sound or movement.

The quest to define electricity is, ultimately, a struggle to find illustrative models - and, as physicists sometimes say, “models can muddle.” The concepts are beyond direct illustration or explanation. One textbook envisages a pipe filled with small balls, with electricity described as an engine pushing the balls along. Another common analogy is with flowing water. Some models unwittingly encourage the mistaken idea that it’s the electrons themselves that flow, and the idea that electrons are “used up” is another common misconception, once described as “the myth of the knackered electron”.

Joan Solomon, in her book Teaching Secondary Physics probably has the best idea, that of an endless chain inside a plastic pipe - and it explains how to make a working model of it.

Pioneers

The story of our understanding of electricity is one of growing insight based on experiment by pioneers. As far back as 600bc, the Greek philosopher Thales observed that a substance which the Ancient Greeks called “electrum” (which we know as amber) would attract particles of straw if it was rubbed on fur or cloth. Two millennia later, in 1600, William Gilbert, physician to Elizabeth I, did further experiments with amber and coined the word “electrica” as a description of substances like amber.

In 1752 Benjamin Franklin flew a kite in a thunderstorm, drew a spark from a key hanging on the kite and so demonstrated that lightning and electricity are the same thing. He had to coin the language for what he was doing, using for the first time in the electrical context such words as “positive”, “negative”, “charge” and “conductor”. In 1831, Michael Faraday demonstrated that you can make electric current flow in a coil of wire by moving a magnet through the coil - the crucial principle of electromagnetic induction. This milestone made possible the electrical generator and the electric motor (essentially these are the same machine, a generator uses moving magnets to induce current, a motor uses current to move magnets).

Faraday is, therefore, the key figure in the development of electricity.

Once electricity could be easily generated, the search was on for practical uses. Lighting was an obvious one. Experimenters were already familiar with the bright spark, or arc, caused when electricity leaps across a gap in a circuit. Making a lamp in which an arc was “struck” between two carbon electrodes was relatively simple, and such lamps were used in public halls and theatres in the 1860s. But they were smelly and smoky, and domestic lighting had to wait for the invention of light bulbs with glowing filaments.The problem was how to make the filament glow without quickly burning out.

In the late 1870s, Thomas Edison in the US and Joseph Swan in England independently made successful electric lamps with the filament held within a vacuum. Later improvements brought the tungsten filament and the nitrogen-filled lamp. Suddenly, you could press a switch and flood a room with light. The town of Godalming had electric lighting in 1881, claiming a world first (although Edison had already lit some New Jersey streets near his laboratory using his own generator).

The new lighting quickly spread, and overhead power lines became familiar on the streets. Once electric lighting made it into the home, there was a gadget bonanza, some of which, such as the electric mousetrap, didn’t survive. Useful appliances were soon invented - cookers and irons in the 1890s, vacuum cleaners at the turn of the century, heaters by

Health

Apart from improving our lifestyle, electricity has also had a big impact on our health. Electricity is in some ways the stuff of life - the fact that heart beats are driven by electrical impulses makes possible dramatic life-saving interventions. In 1924, Willem Einthoven found a way to assess the health of the heart by measuring its electricity - now known as ECG (electrocardiography). And tweaking the electrical impulses can help an ailing heart - we’ve all seen electrical defibrillation on TV: “Stand back, nurse!” (above). The first such revival was carried out by Paul Zoll in the US, on 28 August 1952.

Now there are people walking around with defibrillators implanted in the chest which will automatically kick in to rescue a badly behaved heart.

Many patients, too, have pacemakers implanted to keep the heart beating at a steady rate. Electricity is also used in other therapeutic ways - to destroy certain tumour cells, and to help some kinds of mental illness.

(“Electric shock therapy” - putting electricity through the brain - gained a bad reputation through over-use in the mid-20th century, but properly used it seems to have its place.) The idea of a connection between electricity and the body brought many charlatans out of the woodwork. In the late 19th century you could go to a “consultant medical electrician” for, presumably, some healthy shocks, or you could buy an electric helmet, an electric corset, electropathic socks, Dr Scott’s electric hairbrush, an electrified corset for women wanting to lose some inches or for men there was Dr Moffatt’s electropathic belt for extra vigour (whatever that meant).

The Christchurch Electricity Museum has an example of one of these devices in the form of an “Overbeck Rejuvenator”. Dating from 1929, this gadget (seven guineas for the basic model, 12 for the “Supreme”) was devised and marketed by O.C.G.J.G.L Overbeck, FRSA, FGS, FCS. The accompanying pamphlet lists 36 problems that the machine is effective for, including asthma, lumbago, obesity and wrinkles.

Lower down the scale were the little hand-cranked electric shock machines - and their penny-in-the-slot seaside equivalents - all of which survived into the 1950s and were supposed, somehow, to do you good.

Electrical life-saving is one thing, but once it became clear that electricity could kill (electrical accidents were sensationalised in the late 19th century as “death by wire”), using it became a legal way to kill people. The story of “The Chair” or “Old Sparky” started when a New York State Commission of 1886 examined alternatives to hanging, and execution by electricity was dubbed “electrocution”. It is a tale of rivalry between Thomas Edison and George Westinghouse. Edison was already supplying DC (direct current) electricity commercially, but it was only available within a few miles, and he was having to face up to the advantages of the AC (alternating current) system developed by Westinghouse. Edison perversely campaigned for electrocution by AC because he thought it would aid his cause if the public associated AC with death.

Edison sponsored a series of cruel experiments on animals, including horses and an elephant, showing that AC was more lethal than DC. So it was that one Harold Brown, working for Edison, devised and installed an AC electric chair in New York State prison in 1889. Westinghouse protested, and funded the appeals of some of the early condemned victims - not because he felt sorry for them, but because he was desperately worried that AC electricity would be tainted by death in the minds of customers. His concerns were unfounded. The advantages of AC over DC for all purposes - in particular the ease with which it could be transformed in voltage for long distance transmission - were obvious. Over the years, electrocution was replaced by lethal injection, and remains in use only in the State of Nebraska.

The national grid

Direct current flows in one direction only. Alternating current flows one way and then the other, typically alternating 60 times per second. Early public power supplies were DC. Each town had its own power station - much as it had its own gasworks - supplying the local area. If the generator stopped working, everyone’s lights went off.

The big advantage of AC is that it is easy to use a transformer to change the voltage. Over long distances, where a powerful push is called for, the voltage can be high. Then it can be brought progressively down to the domestic level. AC made it possible to link power stations together in a national grid.

In the UK, the grid dates from the 1930s and operates at 400kV (400,000) volts or 275kV, enabling it to travel long distances without significant loss of power. It is transformed in steps down to 240 volts for the home.

Ideally, the grid carries just enough electricity - too much cuts the profit, too little cuts the lights. It’s a fine balance, and failure risks a chain reaction.

Renewable energy

The government, driven by environmental considerations and declining North Sea gas production, has set out plans to generate more electricity using renewable sources, such as hydroelectricity, wave power, solar-powered cells, geothermal energy (hot water from under the earth) and biomass fuel (made from crops).

Currently, such renewables produce less than 3 per cent of our electricity.

The Government’s aim is to increase this to 10 per cent in 2010 and 20 per cent by 2020 - formidable targets, which will involve building 1250mW (megawatts) of generating power per year for 20 years. (Currently we only have 1200mW of renewable generating power in total.) It is envisaged that although biomass and wave power may become commercially viable, by far the biggest contributor will be wind-driven generators. Huge wind farms (usually offshore) are planned, as well as smaller projects operating at local level.

More local and “micro” (single office blocks and factories) power generation is also expected to be developed, using wind, biomass, local waste and fuel cells in individual buildings.

Buy green

Many power suppliers allow you to sign up to a “green” option. This doesn’t mean that electricity will come straight from the wind farm to your hair-drier - it all comes from the national grid. The supplier promises to buy renewable-source power in proportion to your payments, or to put your money in a fund for future green-power development. Friends of the Earth have a good explanation of this on their website, together with straightforward advice on choosing the best deals.

Jump leads

Electricity can jump one centimetre for every 1,000 volts, which means that if you get too near a high-voltage power line you’re in danger of being converted into crackling. If it’s a 400kV power line, the current can jump four metres. Typical accidents are caused by pylon climbing, flying kites into power lines, and dangling wires from bridges on to railway power lines. That said, given the ubiquity of electrical supply lines, transformers, sub-stations and pieces of high-voltage equipment at work, accidents of that spectacular kind are surprisingly rare.

It’s different in the home, though. A survey last year by retailers Currys, with the Good Housekeeping Institute, showed that many parents are careless with electricity - one in 10 would allow a young child to use a cooker or an iron unsupervised, and only 11 per cent said they had warned their children not to play with switches, plugs and wires.

Victim support line

Abbe Nollet, court electrician to Louis XV, lined up 200 monks and connected them to each other with wire over a total length of 275 metres.

He then demonstrated that an electrical charge applied to one end of the wire made the monks all yelp and jump at the same time. He performed at least two such experiments (the first with 146 French guardsmen), by royal command, in 1746. Of his electrified brothers in Christ he wrote: “The exclamations of surprise were simultaneous, even though they came from 200 mouths.”

In a demonstration to the Royal Society of London in 1720, the scientist Stephen Gray fetched a boy from the street, suspended him above the ground with insulating cords, electrified him with the aid of a well rubbed piece of glass, and then showed he could draw sparks from the lad’s nose. The boy with the sparking nose was an “urchin” from the charitable Charterhouse foundation (and so, presumably, undeserving of too much consideration).

Alexander von Humboldt, working on the relationship between electricity and the body in the late 18th century, stuck electrodes into the fresh cavity left in his own mouth by an extracted tooth, in the hope that the shock would alleviate the pain. He expected that vigorous stimulation of the nerve would suppress the pain response.

Let’s just say he was very disappointed (recent work has shown that electrical stimulation of the right parts of the brain can alleviate pain).