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Schweigger Multiplier

In 1820, the news that the current traveling through an electrical wire could deflect the magnetic needle of a compass astounded the scientific community. Before Hans Christian Ørsted’s announcement of this discovery, scientists considered electricity and magnetism two distinct phenomena. His findings, however, offered hard evidence that they were somehow related. Trying to figure out the specifics of the relationship between electricity and magnetism suddenly became the focus of many nineteenth century laboratories. To help them accomplish their goal, scientists needed better instruments.

Johann Schweigger was a professor of chemistry at the University of Halle in Germany at the time Ørsted gave his fateful lecture at the University of Copenhagen that led to his momentous discovery. Schweigger also served as coeditor of the Journal for Chemistry and Physics, which likely gave him the chance to take an early peak at the treatise Ørsted submitted describing his findings. Within two months of Ørsted’s discovery, Schweigger found a way to amplify the effect that Ørsted first observed. Instead of trying to deflect a compass needle with a straight wire carrying an electric current, Schweigger used a wire formed into a coil with multiple turns looped around a rectangular frame, in the center of which the magnetized needle was suspended. As he happily discovered, the coiling of the wire amplified the magnetic field produced by the current flowing through it, deflecting the needle farther than before. And the more turns he added, the more deflection he saw.

Schweigger aptly called his coil and compass needle setup a multiplier, since it multiplied the effect of an electric current on a magnetized needle. On September 16, 1820, he gave a paper presentation at the University of Halle describing the multiplier and the experiments he performed with it. The following November, Schweigger’s paper appeared in Germany’s Literary Gazette. His invention made a tremendous impact on the blossoming field of electromagnetics. With the Schweigger multiplier, researchers could detect even extremely weak electric currents. At the time, no other device could match its sensitivity, making it a popular galvanometer. Galvanometers are devices used to detect and measure electrical currents. Without them, scientists would have made very little headway in understanding electromagnetism.

Not long after Schweigger developed his multiplier, similar instruments began popping up in different areas. In Schweigger’s homeland, Berliner Johann Poggendorf built a multiplier in 1821. In England, University of Cambridge professor James Cumming built a galvanometer that worked on the same principle as Schweigger’s and Poggendorf’s, but took it one step further. He added an extra magnet to his apparatus to counterbalance the magnetic field of the Earth. Cumming built his device in 1821 and his work describing the early galvanometer was published the following year. Other scientists further perfected Schweigger’s device, including Leopoldo Nobili, Emil Heinrich Du Bois-Reymond, and even the man who started it all, Hans Christian Ørsted.

The Schweigger multiplier inspired the groundbreaking work of another important pioneer in electromagnetics – American Joseph Henry. In the mid 1820s, Henry attended a lecture by William Sturgeon in which the English scientist demonstrated his new invention, the electromagnet. It consisted of a piece of iron with wire wrapped around it attached to a battery that provided an electric current to the wire. His earliest version produced a magnetic field strong enough to lift just under 10 pounds. Intrigued, Henry wanted to build his own, more powerful electromagnets. Recalling Schweigger’s multiplier, Henry coiled more and more wire around the iron bases of his electromagnets. Just as with the multiplier, the increase in turns of wire produced an increase in magnetic field strength. This, along with Henry’s use of insulation around the wire, eventually enabled him to build incredibly strong electromagnets capable of lifting thousands of pounds.

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