Wire electromagnet core made by James Joule for electromagnetic engine, c.1839. Used to experiment on the design of wire most suited for Joule's electromagnetic engine. The practical advantage of the solid electromagnet outweighed the wire magnet. Described in Joule's 1839 paper 'On the use of Electro-magnets made of iron Wire for the Electromagnetic Engine'.

Sixteen square iron wires bound together and bent into shape. Has lost its envelope of cotton, together with 16 feet of covered copper wire 1/16 inch in diameter.