Carl August Steinheil: Earth return technique


In 1837, scientists studying the budding technology known as telegraphy were grappling with ways to more affordably create a circuit to carry telegraph signals and return currents over long distances. Since 1820, two wires were required to accomplish the task. But cabling was, much like the fiber optic lines of today, a very expensive material.

Karl A. Steinheil

Steinheil (Image source: Wikipedia)

Munich University Professor Carl August von Steinheil found the solution by accident. Steinheil was investigating an idea put forth by mathematician Carl Friedrich Gauss—that a railway line's two rails could be used to create a circuit. The experiment failed, as the rails were not sufficiently insulated. But Steinheil discovered something else: the ground itself could be used as a conductor to complete the electrical circuit.

The earth return method played a key role in the installation of the first telegraph circuit in the United States, between Washington, D.C. and Baltimore. Samuel Morse's original plans called for two metallic conductors to complete the 40-mile circuit, but cost overruns and technical issues of the almost seven-year project led him to adopt earth return before the first public trials began in 1844.

Earth return had its problems, naturally. Damp ground is the best medium for transmitting current, so dry weather was an issue for telegraph stations as the dry ground increased resistance. And it was completely unsuitable for voice transmission because of interference from other power systems and electrical circuits. In 1883, the two-wire, metallic circuit system was reintroduced. Still, Steinheil's discovery was an important factor in the growth of telegraphy, helping reduce the cost of building out telegraph systems worldwide.

Steinheil didn't rest on his laurels—in fact, he didn't profit directly from the earth return method as he refused to patent it, "dedicating it instead to the benefit of the public," writes Andrew Wheen in Dot-Dash to Dot.Com. He continued his work in telegraphy in the 1840s, helping design Austria's telegraph network and Switzerland's network. A physicist, engineer and astronomer, Steinheil made a big mark in the field of optics, particularly in astronomy. His work with Leon Foucault paved the way for reflecting telescopes. He created the first daguerreotype in Germany in 1839 using the "Steinheil method," and he is credited with the invention of the photometer.