Stephen Gray (scientist) - Conduction Discoveries

Conduction Discoveries

One night, in his Charterhouse rooms, he noticed that the cork in the end of his tube (needed to keep moisture and dust out) generated an attractive force on small pieces of paper and chaff when the tube was rubbed. When he extended the cork with a small fir stick plugged into the middle the charge was evident at the end of the stick. So he tried longer sticks, and finally he added a length of thread connected with an ivory ball. In the process he had discovered that the "electric virtue" would carry over distance, and that the ivory ball would act to attract light objects as if it were the electrified glass tube.

Over the next few days he extended the reach of his thread-wire (he only had a short piece of wire, and didn't understand the significance of metal as a conductor), and on a number of visits to wealthy friends in Kent (Flamsteed's relatives, and the Reverend Granville Wheler) he extended his experiments through thread laced up and down through the large rooms of their manor houses, then down from the tower to the courtyard, and eventually out, across the paddocks to a distance of 800 feet.

In the process, Gray and Wheler discovered the importance of insulating their thread 'wire' from earth contact, using silk (which is less of a conductor than the hemp pack-thread they used as their main conductor). They noticed that wire supports to the pack-thread leaked away the electrical charge, and discovered that electricity would carry around bends in the thread and that it appeared unaffected by gravity if the thread was hung from the tower.

From these experiments came an understanding of the role played by conductors and insulators (names applied by John Desaguliers). C.F. du Fay, a French scientist, visited Gray and Wheler in 1732, saw the experiment, and returned to France where he formulated the first comprehensive theory of electricity called the "two-fluid" theory. This was taken up by his associate, the Abbé Nollet, and opposed (to a degree) by Benjamin Franklin's group in Philadelphia -- where Franklin and English experimenters Beavis and Watson, had devised a single-fluid/two-state theory (later given the terms positive and negative by Watson) which eventually prevailed.

Gray went on to make more electrical experiments, inducing electrical polarity in suspended objects (he invented the famous "Flying Boy" demonstration - a boy suspended on silk cords, who was charged and attracted chaff, paper, etc., to his hands). He certainly realised that his phenomenon of 'electric virtue' was the same as lightning, many years before Franklin formulated his flying-kite theory.

When Sloane took over the Royal Society on Newton's death, Gray belatedly received the recognition denied him by the Newton faction. He was given the Society's first Copley Medal in 1731 for his work on conduction and insulation, and also its second in 1732 for the induction experiments. In 1732 he was also admitted as a member of the Royal Society, but he died destitute a few years later in 1736.