Desaguliers

Jean Theophile Desaguliers was a British scientist who introduced in science definition of electrically conductive and non-conductive materials.

Jean Theophile Desaguliers was born on March 12, 1683. He was a son of a Protestant minister, a Huguenot who sought refuge in England in 1685 after the Revocation of the Edict of Nantes.

Jean Theophile Desaguliers, a demonstrator for the Royal Society, made the first generalizations of the two kinds of electricity. 1) A body electrical per se, is such a body in which one may excite electricity by rubbing, patting, hammering, melting, warming, or any other action on the body itself. 2) A non-electric is such a body as cannot be made electrical by any action upon the body itself immediately, though it is capable of receiving the virtue (electricity) from an electric. Non-electrics were called conductors by Desaguliers. This sounds like a contradiction in terms, but if you realize that a piece of metal can not be electrified by rubbing you may see the connection.

Between 1729 and 1736, two English friends, Stephen Gray and Jean Desaguliers performed a series of experiments which showed that a cork or other object as far away as 800 or 900 feet could be electrified by connecting it to a rubbed glass tube with materials such as metal wires or hempen string. They found that other materials, such as silk, would not convey the effect. As a matter of fact, they discovered in early, painstaking experiments that the distant object would not become electrified if the transmission line made contact with the earth, but only if they separated or insulated it from the earth by suspending it on silken threads.

Gray had previously shown that solid or hollow objects of any given material behave the same way when electrified. 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.

Jean Theophile Desaguliers was an ardent advocate of Newtonian optics, on which he lectured and gave demonstrations. His research on colour and binocularity was important for the science. In 1716 Desaguliers reported a method of binocular combination that became widely employed in other studies of binocular vision, namely, placing an aperture in such a position that two more distant, adjacent objects were in the optical axes of each eye. Under these circumstances red and green patches of silk did not mix after the manner of combining prismatic lights, but engaged in rivalry. Desaguliers also investigated size perception and showed that apparent size was determined by apparent distance rather than physical distance. Moreover, he did not base his conclusions on his own observation but on those of 'any unprejudiced Person'. Thus, both stimulus control and the use of the unbiased observer were employed in eighteenth century experimental studies of vision.

Printed from the original engraving of Hans Hysing, 1678-1752.

Jean Theophile Desaguliers designed instruments and devices for different areas of science and technology, including astronomy and even diving.

The Virtual Orrery - an apparatus that illustrates the relative positions and motions of bodies in the solar system by rotation and revolution of balls moved by wheelwork; sometimes incorporated in a clock (J.T. Desaguliers, Course in Experimental Philosophy).

Jean-Théophile Desaguliers, A Course of Experimental Philosophy, London, 1744, Vol. II, Pl. XX, Fig. 7 8.

Model of a diving bell designed by Desaguliers