Joseph Henry's electromagnet with 450 turns, 1828.
© Science Museum / Science & Society Picture Library
Reconstruction made in 1931. In 1825, English inventor William Sturgeon (1783-1850) wound a coil of wire around an iron rod and made one of the first electromagnets. The American physicist Joseph Henry (1797-1878) improved considerably on Sturgeon's design by using many turns (450 in this case) of thin, insulated wire. In 1831, Henry supervised the building of an electromagnet at Yale University which was capable of lifting a tonne.