Electricity before Franklin

Before it was something you measure, electricity was a parlour curiosity for two thousand years. To understand why Franklin had to bet on a sign, and why the current arrow still runs from plus to minus, you have to see what people had in front of them before him: not a current, not a charge, an attraction.

The Greeks knew that amber, the yellow fossil resin polished into jewellery, attracts bits of straw and hair right after it is rubbed. The observation is credited to Thales of Miletus, six centuries before our era. Amber is ēlektron in Greek. For two millennia, that is about all anyone knows of it. The lodestone, which attracts iron without being rubbed, draws more interest, above all once the compass puts it to work for sailors.

In 1600, William Gilbert, a London physician and soon the Queen’s, publishes a great book on the magnet and gives one chapter to the other attraction. He rubs everything within reach and finds that amber is not alone. Glass, sulphur, sealing wax, many stones do the same. He invents a small instrument, a light needle on a pivot, which swings toward the rubbed body and betrays the faintest attraction. To name all these bodies that behave like amber, he coins a Latin word from the Greek, electricus. The word "electricity" descends from it. Gilbert thinks rubbing releases a kind of vapour that leaves the body and draws light things back toward it. He sets this attraction cleanly apart from the magnet’s, and that is already a great deal.

Over the following decades, people learn to make more of it. Around 1663, Otto von Guericke, the burgomaster of Magdeburg known for his hemispheres and his vacuum pump, casts a sulphur ball the size of a child’s head, mounts it on an axle and rubs it with his hand as it turns. The ball attracts feathers, then pushes them away once they have touched it, and in the dark it glows. Around 1705, Francis Hauksbee, in London, spins a glass globe emptied of its air and gets, inside it, a violet glow bright enough to read by. There are electricity machines before there is the least idea of what they do.

In 1729, a dyer turned scientist by passion, Stephen Gray, changes the question. He rubs a glass tube stoppered with a cork and notices that the cork attracts too, though nobody rubbed it. Something has passed from glass to cork. He sticks a rod into the cork, then a hemp string, and the attraction turns up at the far end. He lengthens the string. In July 1729, at the home of his friend the Reverend Granville Wheler in Kent, they run it through a gallery, then a barn, hung from silk threads, Wheler’s idea, and the electric virtue passes along hundreds of feet of hemp. When they replace the silk with brass wire to hold the string up, nothing reaches the end any more: the brass has let it all leak away. Gray has just found that electricity travels, and that bodies fall into two families, those that let it run and those that hold it back. Our conductors and insulators were born in that barn, even if the words come later; "conductor" is Desaguliers’s, in 1739.

To show it, Gray hangs a boy from silk cords, flat in the air, brings the rubbed tube near his feet, and leaves of metal fly up to his hands and face. The flying boy experiment goes round Europe; in Paris, the abbé Nollet repeats it before society and makes it the picture of his book. The Royal Society gives him its first Copley Medal in 1731.