Drawing of first electromagnet invented in 1824 by British scientist William Sturgeon, his original drawing from his 1824 paper to the British Royal Society of Arts, Manufactures, and Commerce . It was made of 18 turns of bare copper wire (insulated wire had not been invented) on a U-shaped lacquered iron core about 1 ft (30 cm) long and 1/2 inch (13 mm) diameter. When the wires were connected to a single cell copper-zinc-acid battery, the electromagnet could support 9 pounds. The little cups contain mercury and were an early method of making an electrical contact between wires. The one on the left acts as a power switch. Alterations to image: converted from JPG to 32color PNG. (Detailed information is from Sylvanus P. Thompson (1891) Lectures on the Electromagnet , W.J. Johnson Co., New York, p.17-19 )