Frogs' legs and the first battery
In the 1780s an Italian doctor, Luigi Galvani, noticed that the legs of a dead frog twitched when touched with two different metals. He thought he had found a special animal electricity. His friend and rival Alessandro Volta disagreed: the electricity, he argued, came from the two metals, with the damp frog simply completing the path. To prove it, in 1800 he stacked discs of zinc and copper separated by cloth soaked in salt water, and got a steady flow of electricity with no frog at all. It was the first BATTERY.
Some animals really do make electricity. The electric eel of South American rivers, actually a kind of knifefish rather than an eel, can deliver a shock of more than 800 volts to stun its prey.
Benjamin Franklin's words
Benjamin Franklin experimented with electricity in the 1740s and 1750s and needed words to describe what he saw. Several he coined or popularised are still in use: CHARGE, POSITIVE and NEGATIVE, and battery, which he borrowed from the military word for a row of cannons, for a row of linked glass jars that stored electricity. His famous kite flight in a thunderstorm in 1752 showed that lightning is electricity. It was extremely dangerous: the following year a scientist in Russia, Georg Richmann, was killed trying a similar experiment.
STATIC electricity builds up when two materials rub together and ELECTRON particles pass from one to the other, as when you pull off a jumper or rub a balloon on your hair. It is worst on dry days, because moist air lets the charge leak away. How the biggest SPARK of all forms is on our weather page.
Why birds can sit on power lines
Electricity only flows when there is a complete loop, a CIRCUIT, for it to travel round. A CURRENT is a flow of electrons along a WIRE, measured in amps, after the French physicist André-Marie Ampère; VOLTAGE is the push that drives it. A CONDUCTOR, such as copper, lets current flow easily, while an INSULATOR, such as plastic or rubber, stops it, so wires are copper wrapped in plastic. A bird sitting on a single power line is safe because it offers no path to the ground or to another wire; the current simply carries on along the line.
RESISTANCE is how hard it is for current to get through. In an old-fashioned light BULB, a very thin filament resists the current so strongly that it heats up until it glows white-hot. A SWITCH simply makes or breaks the circuit, and every battery has a positive and a negative TERMINAL.
Magnets, motors and a wandering pole
In 1831 the English scientist Michael Faraday found that moving a MAGNET in and out of a coil of wire made electricity flow. Nearly every GENERATOR in every power station works the same way today, spinning magnets and coils to make POWER, and running the idea backwards gives the electric motor. Our inventors page covers the people who built the electric age on it.
The Earth itself is a giant magnet, so a COMPASS needle swings to point north. Its magnetic north pole wanders: it has been drifting from northern Canada towards Siberia by tens of kilometres a year. Every few hundred thousand years the whole field flips, so that north and south swap; the last time was around 780,000 years ago.