William Sturgeon and his galvanometer

William Sturgeon (1783-1850) is an unfamiliar name in most households, but his experiments and the instruments that he built were central in the annals of electrical engineering. He was an educator as well, with an incisive writing style that engaged the interest of fellow scientists and laypersons.

An important year in his life and in the emerging field of electrical engineering was 1824. Inspired by Hans Christian Ørsted’s observation that a magnetic needle is deflected by current flowing through a nearby conductor, Sturgeon built the first electromagnet that was capable of lifting more than its own weight. One model he built consisted of a seven-ounce piece of iron that could lift nine pounds when current passed through wire wrapped around it. This achievement paved the way for the inventions of the telegraph, electric motor and a vast number of derivative devices. Sturgeon actually was first, in 1832, to build a viable dc electric motor with a commutator.

Spurned by a staid publication called Philosophical Transactions, Sturgeon responded by founding a more accessible periodical known as Annals of Electricity, Magnetism and Chemistry. Today it may be seen in Google Books, and it makes very interesting reading.

In the years that followed, Sturgeon continued to experiment, theorize and publish his findings about a great many phenomena associated with electromagnetism. He built electromagnets, energized them, heated them, bent them, cut them, and took all sorts of measurements, publishing his findings in language that was comprehensible to many readers without technical training.

Among his many inventions was the suspended-coil galvanometer. It is a sensitive ammeter that causes a needle to pivot when current flows through the associated coil. A full-function multimeter can be built based on the galvanometer configured to read current. A dc voltmeter can be constructed by putting the galvanometer in a voltage divider circuit, calculating the voltage required to cause a specified current, and calibrating the dial appropriately. The ohms function is created by placing the device to be measured in series with an internal battery and calibrating the dial in ohms, kilohms and megohms as required.

Among Sturgeon’s many other achievements included an improved version of the chemical battery and a comprehensive theory of thermoelectricity. In addition, he performed a great number of atmospheric observations, using a kite to measure the charge of the atmosphere at various altitudes. He found that it became more positively charged with respect to the earth as the altitude rose.