Kent Scientists

Stephen Gray (1666-1737)

Experimental Philosopher from Canterbury.

His pioneering experiments advanced our understanding of electricity

In April 1730 an elderly pensioner in a London almshouse, the Charterhouse, was carrying out experiments in his room. In one of these he suspended a 9 or 10 year-old boy horizontally from the ceiling by means of two ropes and then ‘electrified‘ him. This painless procedure involved taking a glass tube, rubbing it to charge it up and holding it near but not touching the boy’s feet. The surprising result was that small pieces of metal foil, placed on a tray below the boy spontaneously jumped up and attached themselves to his face and hands. In the language of the time this showed that the ‘electrical vertue’ was communicated from the tube to the boy and spread throughout his body.  

Stephen Gray, who performed these experiments, was no ordinary amateur scientist. Born in Canterbury in 1666, he went into the family dyers’ business and ran it for many years.  Despite the arduous and unpleasant nature of this trade, he found time to pursue various scientific interests. These included devising a microscope which used a drop of water as a lens, and observing sunspots and eclipses. With the help of his brother who was Mayor of Canterbury, Gray made contact with the Astronomer Royal, John Flamsteed, and the President of the Royal Society, Sir Joseph Banks, and corresponded with them on scientific matters. (One curious assignment given to him by Flamsteed was to investigate reports of a ghostly apparition, in which a Mrs Veal was apparently seen and conversed with in Canterbury, twenty-four hours after she had actually died in Dover. The incident caused a stir in London as well as Canterbury and even came to the attention of royalty. Gray interviewed witnesses but was unable firmly to confirm or deny their credibility.)  

Gray's 'electrified boy' experiment 

At the age of fifty, Gray moved to London and was appointed assistant to the curator of experiments at the Royal Society whose role was to lay on demonstrations at the Society’s meetings. He also began the programme of investigations for which he is most remembered, into the properties and behaviour of electricity. (This was what today is called static electricity – the sort that can produce a spark when you stroke a cat on a frosty night.)  

The pioneering experiments which Gray carried out in 1728-9 were intended to discover how far an electric charge could be made to travel. He described these in a number of lengthy letters published, along with other ‘Philosophical Transactions’, in the Royal Society’s journal. As a source of electric charge he used a glass tube, 1 meter in length and 3 cm in diameter, closed by a cork at each end. As a detector he used first a very light feather and later a small piece of thin brass foil, both of which would be attracted to any charged object. At first he inserted a short wooden rod into one of the corks and attached an ivory pith ball to its end. When he rubbed the tube, a feather was attracted to the ball, showing that electric charge could travel through the wooden rod. (Wood is not a perfect insulator and the tiny amounts of electric charge involved in this experiment could travel through it.)  

Norton Court and Otterden PLace

Estates in Kent where Gray carried out experiments on the transmission of electricity over a distance: Norton Court (left) and Otterden Place (right).

In a sequence of experiments Gray extended the distance that the electric charge could be transmitted through various materials. When his experiments could no longer be carried out within the confines of his London chamber, he moved to the Kentish estates of two friends, first at Norton Court, near Faversham, and finally at nearby Otterden Place. Here he finally managed to transmit charge through a ‘packthread’ cord – similar to strong string – stretched from the building’s turret window, across the garden and an adjoining field, a total distance of 233 metres. Demonstrations of this sort are notoriously tricky to stage and are influenced by the weather, but Gray was a resourceful experimenter. His success was achieved by supporting the packthread at intervals along its length by loops of silk suspended between wooden poles, the silk being a good enough insulator to prevent the electric charge from leaking away.  

Gray continued to demonstrate electrical phenomena at the Charterhouse until his death. His audiences consisted of ladies and gentlemen, including Fellows of the Royal Society, who rewarded him with an Honorary Fellowship and the prestigious Copley Medal, awarded annually for the most important scientific discovery of the time.  

Pylon

Stephen Gray, the man who showed that electricity can be transmitted over distances, and clarified the role of conductors and insulators, died in 1737 and has no known grave. His best memorial is perhaps in the pylon lines which criss-cross the countryside today, reliant on conductors and insulators for the transmission of the electric power so essential to modern life. One such line in Kent passes a mile or so north of Otterden Place, where Gray experimented nearly three centuries ago.

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