Benjamin Franklin was famous for many things – perhaps most of all the kite experiment he devised to prove for the first time that lightning is electricity.
BenjaminFranklin was a multi-talented man, famous for many things – perhaps most of all the kite experiment he devised to prove for the first time that lightning is electricity.
Born in Boston, Franklin (1706–1790) was an inventor, philosopher, musician and statesman.
He was one of the Founding Fathers of the United States and signed both the Declaration of Independence and the Constitution.
His kite experiment did not involve simply directing a lightning bolt down the string, which would almost certainly have killed him.
Instead he used the kite to draw charge from the bottom of a thundercloud.
Then he placed his knuckle on a metal door-key he had run up the string – and felt a spark.
As a result of his interest in electricity, Franklin invented the lightning rod, which protects buildings by conducting charge from thunderclouds safely to the ground.
But Franklin’s experiment with electricity was by no means the first. In fact the strange, invisible forces of electricity and magnetism had been known since ancient times.
Many materials become ‘electrically charged’ when rubbed together, and several minerals are naturally magnetic.
The Chinese had been using one of these, magnetite, in compasses from the 4th century or earlier.
The first person to investigate magnetism and electricity scientifically was William Gilbert (1544–1603), personal doctor to Queen Elizabeth I.
His book De Magnete (On Magnets), published in 1600, described how he made a magnetised model of Earth.
Like any magnet, it had a north and south pole, and when Gilbert moved a magnetic compass around his ‘Earth’ it always pointed to the poles – as a real compass does on the real Earth.
Gilbert suggested magnetism keeps Earth and the other planets in orbit around the sun.
Nearly 80 years later, German physicist Otto von Guericke (1602–1686) said he thought electricity was responsible.
In 1687, Isaac Newton (1642–1727) used his laws of motion to show how the mysterious force ‘gravity’ provided a mathematical explanation.
Von Guericke made the first machine to produce constant electric charge – a friction generator.
It was a ball of sulphur mounted on a spindle, with a handle to make it spin.
Touching the ball as it rotated charged it – and whatever you touched it with – with electricity.
In the early 18th century, this became the standard way to produce electricity for experiments, though the sulphur ball was replaced with a glass one.
In 1745, German clergyman Ewald von Kleist (c.1700–1748) discovered a way to store charge produced by friction generators.
Around the same time, Dutch physicist Pieter van Musschenbroek (1692-1761) invented the same thing. The device is called the Leyden Jar, after his home town.
The 18th century was the heyday of experiments with static electricity.
Most scientists assumed electricity and magnetism were invisible, weightless ‘fluids’.
The word ‘charged’ was first used at this time, to mean filled-up – i.e. with electrical ‘fluid’.
We now know that electricity is a property inherent in some subatomic particles.