Fitxer:Joseph Henry electromagnet.png

English: Drawing of large electromagnet and associated equipment built by American scientist Joseph Henry and used in his pioneering experiments on electromagnets around 1830, published in Scientific American magazine, 1880. Although William Sturgeon built the first electromagnet in 1824, Henry built the first multilayer magnets, researched, developed and popularized them, and is responsible for the modern form of electromagnet. The magnet shown consists of a "U" shaped iron core wrapped with many turns of silk covered wire. A smaller "U" shaped piece of iron, bridged across its poles, is attached to the lever on the wooden frame, and is used to measure how much force it takes to pull the second piece of iron off the poles of the magnet. The equipment at bottom, described in source caption, consists of a liquid battery cell to power the electromagnet, a "current reverser" switch, and coils used with the magnet to demonstrate induction. The magnet was preserved at Princeton University, and is now in the Smithsonian collection.