In 1822, French physicists Arago and Lusak discovered that when an electric current passes through a winding in which iron is present, it can magnetize the iron in the winding. This is actually the initial discovery of the electromagnet principle. In 1823, Sterkin did a similar experiment: he wound 18 rounds of copper bare wires on a U-shaped iron bar that was not a magnet, and wound around U when the copper wire was connected to a voltaic battery. The copper coil on the iron rod generates a dense magnetic field, which makes the U-shaped iron rod an "electromagnet." The magnetic energy of this kind of electromagnet is multiplied more than that of the permanent magnet. It can take up 20 times more weight of iron than it does, and when the power is cut off, the U-shaped iron rod cannot absorb any iron, and it becomes a new one. Root ordinary iron rod. Sturgeon's electromagnet invention made people see the bright prospect of converting electrical energy into magnetic energy. The invention soon spread in Britain, the United States, and some coastal countries in Western Europe. In 1829, the American electrician Henry made some innovations to the Sterkin electromagnet device. Insulated wire replaces bare copper wire, so there is no need to worry about being short-circuited by copper wires. Because the wires have an insulating layer, they can be wound tightly around a circle, because the denser the coil, the stronger the magnetic field generated, which greatly improves the ability to convert electrical energy into magnetic energy. By 1831, Henry tried out a newer electromagnet. Although it was not big, it could suck up 1 ton of iron. The invention of the electromagnet also greatly increased the power of the generator.