English: A powerful electromagnet built by American scientist Joseph Henry around the 1830s. The electromagnet was invented by William Sturgeon in 1823, but Sturgeon's electromagnets were weak because without insulated wire he was only able to use a single spaced out layer of wire on iron cores. Henry created the first powerful electromagnets. By using wire insulated by silk he was able to make electromagnets with multilayer windings with thousands of turns like this one, which created strong magnetic fields which could lift thousands of pounds. According to the source text, this magnet was apparently overheated by passing excessive current through the windings, causing the charred areas.