Stephen Gray, a British chemist, is credited with discovering that electricity can flow (1729). He found that corks stuck in the ends of glass tubes become electrified when the tubes are rubbed. He also transmitted electricity approximately 150 metres through a hemp thread supported by silk cords and, in another demonstration, sent electricity even farther through metal wire.
Gray concluded that electricity flowed everywhere. Stephen Gray was born in Canterbury, Kent, England and baptised on December 26th 1666. His father, Mathias Gray, was a dyer, described as a rapidly rising artisan. Stephen Gray had no formal education in a University, but probably studied in London or perhaps in Greenwich under John Flamsteed. Somewhere he acquired working Latin. Until disabilities made it impossible, he was a dyer like his father. However, Stephen Gray cultivated science as a hobby. In his writing, Gray has the confidence of a self-taught man.
His friendship with John Flamsteed (of Denby, Derbyshire – the first Astronomer Royal) most likely fired his interests in astronomy. From the 1690s to 1716 Gray devoted his scientific energies to astronomical observations, quantitative and accurate, of eclipses, sunspots, the satellites of Jupiter, and the like. In a letter, of May 12th 1697, Gray informed readers of The Philosophical Transactions of the Royal Society of his use of water lenses and described a “Natural reflecting Microscope”.
More papers followed on: “Microscopy, Concave specula, An accurate way to read height of mercury in a barometer, Haloes and the Sun, Fossils in Reculver Cliff, Sunspots, Solar Eclipse May 12th 1706″. He frequently sent the Society and his friend, English Astronomer Royal John Flamsteed, ideas for simple but revealing experiments and reports of geological and astronomical observations. 63 manuscript letters survived, at the British Library, the Greenwich Observatory, and the Royal Society.
It is clear that Gray was an accomplished observer, to the extent that Trinity College, Cambridge, hired him as an assistant in its planned observatory. For the most part his long relationship with Flamsteed does not appear as patronage. It is impossible to imagine his appointment at Trinity without Flamsteed’s assistance, however. In 1707-8, Gray was resident in Trinity, as an assistant to Cotes in setting up the observatory there.
In the latter years of his life he devoted himself to electricity. His electrical interests first appear in a letter of 1708 to Hans Sloane, in which he described the use of down feathers to detect electricity. He is obviously fascinated by lights produced by rubbing a glass tube to charge it and realizes electricity and the lights are related. The idea of an effluvium released from the tube is giving way in his thoughts to ideas of a virtue, something akin to gravitational attraction and electrical conduction.
At a meeting in Somerset House, on April 7th, 1718, Stephen Gray was nominated by the Prince of Wales (later George II) to be admitted as a Pensioner to the Charterhouse in London. Whilst a Pensioner of the Charterhouse (a combination monastery, boy’s school and old man’s home) he carried out, in his sixties, his experiments on electricity.
A lecture at the Charterhouse on discoveries in electricity by Stephen Gray. The diagram above the speaker shows the first electric telegraph at Otterden House, Faversham, of July 1729.
Stephen Gray demonstrated that the static charges of electricity can be conducted by some materials. Between 1729 and 1736 Stephen Gray gave the results of many experiments which showed that the electric virtue of a tube of glass, that had been excited by friction, could be conveyed to other bodies thereby giving them the ability to attract and repel light bodies.
Gray and a friend, Jean Desaguliers, conducted experiments which showed that objects such as cork, as far as eight or nine hundred feet away, could be electrified by connecting them to the glass tube with wires or hempen string. They found material such as silk would not convey electricity. They discovered distant objects could not be electrified if the transmission line made contact with earth.
The line for transmission was suspended by silk threads to prevent contact with the ground. It was found that metal objects held in the hand and rubbed showed no signs of electrification. However, when mounted on a non-conductor, they became electrified. Gray realized that somehow the earth was responsible for conducting electrical charge away from the body. After this realization Gray found he could electrify any material on earth by friction.
He even went as far as to suspend pupils of the house by cords and electrified them, sometimes even drawing sparks from the human body. The figure shows that the electric force of a rubbed glass could be sent, throught a wire, to the body of a person.
From all these experiments, it became clear that electrification is a surface effect; that the electric “virtue” or “fluid” would move freely along some materials-named, by Desaguliers, “non-electrics” or “conductors” – from one body to another. The earth, the human body, metals, moisture are immediately recognized as conductors. Materials which do not conduct electricity came to be called nonconductors or insulators. A metal rod or sphere when held in the hand and rubbed with fur shows no sign of electrification, but when mounted on a nonconductor, the metal is readily electrified. The electrical charge is no longer conducted away to be shared with the huge object which is the earth. When this was realized, it was found that practically any material can be electrified by friction.
Water is found to be a conductor. It renders insulators conducting when the surfaces are wet or moist. This makes understandable the rapid loss of charge by electrified bodies on humid days.
So Gray is credited with finding that electrical conductors must be insulated and that insulators were not conductors and that a charge could be induced in a previously non-electrified body. He established electricity as a current showing it would travel over a conductor. Gray found water to be a conductor which rendered insulators into conductors when their surfaces were wetted. This concept helps us to understand the rapid loss of charges on humid days by electrified bodies. He sent many of his papers to the Royal Society and was elected a fellow. Gray’s most important work, published in 1732, announced the discovery of electrical induction and the distinction between conductors and insulators.
Gray hypothesized that electricity flows everywhere, and he paved the way for more than a generation of “electricians” – wandering scientists who made their living by demonstrating the electric current using Leyden jars. Electricians typically killed birds and other small animals with electric shock and passed electric current across rivers and lakes.
He was awarded the Copley Medal in 1731 (the first award) and again in 1732 for his research on electricity. In his later years Gray was frequently resident with John Godfrey, Esq., (who had also been, note, a patron of John Harris) of Norton Court, Kent, and with the Rev. Granville Wheler, a properous cleric, both of whom aided his experiments in electricity and gave him financial support. He continued his research until upon his death bed 15th February 1736) where he tried to describe to his doctor the work he still needed to complete.