a French chemist who discovered that electrical charge had both positive and negative values. From the mid-18th through the early 19th centuries, scientists believed that electricity was composed of fluid. In 1733 Du Fay announced that electricity consists of two fluids: "vitreous" (Latin for "glass"), or positive, electricity and "resinous," or negative, electricity. In connection with his experiments, when he suspended a thread on glass poles, Du Fay noted that a certain amount of the current was lost to the surrounding air. He thus recommended that the cords be wrapped with some nonconductor so as to be "insulated," or "isolee" as he said, first making use of this term. In 1732, the king appointed Du Fay superintendent (director) of the royal gardens in Paris (Jardin du Roi). As a result, he became an active botanist. In the last years of his life Du Fay focused his work on the optical properties of crystals.