Marconi's Transatlantic Radio (1901): Signals Across the Ocean

Guglielmo Marconi’s transatlantic radio experiment of 12 December 1901 was the first claimed reception of a wireless signal across the Atlantic Ocean. At Signal Hill in St John’s, Newfoundland, Marconi reported hearing the Morse code letter S, three short dots, sent from his station at Poldhu in Cornwall, about 3,500 kilometres (2,200 miles) away. The feat, though doubted by some, showed that radio waves could travel far beyond the horizon and launched the age of long-distance wireless communication.

Background: from Hertz to wireless telegraphy

In the 1860s James Clerk Maxwell predicted that light was one form of electromagnetic wave (see Maxwell’s electromagnetic theory). In 1887 Heinrich Hertz produced and detected such waves in his laboratory in Karlsruhe (see Hertz and radio waves). Scientists including Oliver Lodge in Britain, Édouard Branly in France and Alexander Popov in Russia soon improved the detectors, notably the coherer, a glass tube of metal filings that conducted better when struck by radio waves.

Guglielmo Marconi was born in Bologna on 25 April 1874, the son of an Italian landowner and Annie Jameson, of the Irish whiskey-distilling family. Largely self-taught, he began experimenting at his family’s Villa Griffone near Bologna in 1894–1895 and soon sent signals over hills more than a kilometre away. His key insight was practical: taller aerials and an earth connection greatly increased range. He was not a trained scientist, and he relied heavily on published research and on skilled assistants, but he combined persistence with a clear sense of what customers such as navies and shipowners needed.

Building a business in Britain

Finding little interest in Italy, Marconi moved to London in 1896, aided by his mother’s connections. He filed a British patent in June 1896 and won the support of William Preece, chief engineer of the Post Office. In May 1897 he signalled across the Bristol Channel, and in July 1897 he founded the Wireless Telegraph and Signal Company, renamed Marconi’s Wireless Telegraph Company in 1900.

Progress was rapid. Messages crossed the English Channel in March 1899, and ships began to carry Marconi equipment. Most experts, however, believed that radio waves travelled in straight lines and would be lost into space beyond the horizon, limiting range to a few hundred kilometres. Marconi was convinced they would follow the curve of the Earth.

He also faced fierce competition. Rival inventors and companies in Germany, the United States and elsewhere were developing their own wireless systems, and the cable companies had every reason to resist a cheaper competitor. A spectacular long-distance success would bring publicity, investors and contracts with navies and shipping lines.

Poldhu and the great gamble

Marconi decided to attempt the Atlantic crossing, partly to show that wireless could compete with the submarine telegraph cables that had linked Europe and America since the 1860s (see the first transatlantic telegraph cable). In 1900–1901 he built a powerful transmitting station at Poldhu, on the Lizard peninsula in Cornwall. The physicist John Ambrose Fleming of University College London designed the high-power transmitter, far stronger than anything used before.

A matching station was built at South Wellfleet on Cape Cod, Massachusetts. Both sites had huge circles of wooden masts carrying the aerials, and both were wrecked by storms in 1901: the Poldhu masts collapsed in a gale on 17 September, and the Cape Cod aerial was destroyed in November. Rather than wait, Marconi rigged a simpler fan-shaped aerial between two masts at Poldhu and decided to receive, not transmit, in North America using temporary equipment.

Signal Hill, December 1901

Marconi sailed to Newfoundland with his assistants George Kemp and Percy Paget, arriving at St John’s on 6 December 1901. They set up a receiving station in a disused hospital building on Signal Hill, a rocky headland overlooking the harbour and close to the easternmost point of North America.

Without masts, they had to lift the receiving wire with balloons and kites. A balloon broke away in the strong winds, so on 12 December they flew a kite carrying an aerial wire about 150 metres (some 500 feet) long. By prior arrangement, Poldhu transmitted the letter S repeatedly during set hours of the afternoon in Newfoundland.

Marconi listened through a telephone earpiece connected to a sensitive detector. At about 12:30 pm local time he reported hearing the faint clicks of three dots and handed the earpiece to Kemp, who also heard them. They reported hearing the signal again later that afternoon, though attempts on the following day were less certain. Marconi announced the result to the press on 14 December, and it made headlines around the world.

Many responses were enthusiastic, and Alexander Graham Bell offered Marconi the use of his estate on Cape Breton Island in Nova Scotia for further experiments. Investors and governments took notice, and the Marconi company’s reputation as the leader in wireless was strengthened. Within days, however, cable company interests and some scientists began to question what exactly had been heard.

Doubts and confirmation

The claim was questioned from the start. No independent witness heard the signal, the clicks were faint and could have been confused with atmospheric noise, and only a simple letter was received. Some later engineers have argued that the transmitter’s likely wavelength and the daytime conditions would have made reception at that distance very difficult, while others think it was possible. There has also been controversy over the detector, a self-restoring coherer whose design was claimed by others in Italy.

Practical proof soon followed. In February 1902 Marconi sailed from Southampton to New York aboard the American liner Philadelphia, with receiving equipment and the ship’s officers as witnesses. Readable messages from Poldhu were recorded at about 1,550 miles (2,500 km), and the letter S at about 2,100 miles (3,400 km). Crucially, reception was far better at night, a clue to the existence of a reflecting layer in the upper atmosphere, proposed in 1902 by Arthur Kennelly and Oliver Heaviside and confirmed by Edward Appleton in the 1920s.

That layer, now known as part of the ionosphere, explains why radio waves did not simply vanish into space beyond the horizon. Electrically charged gases high above the Earth bend and reflect certain wavelengths back to the ground, and the effect is stronger at night, when sunlight is not creating the lower layers that absorb signals. Marconi’s success thus rested partly on physics no one yet understood.

Key people

• Guglielmo Marconi (1874–1937) combined existing scientific ideas with relentless engineering and business skill.
• John Ambrose Fleming (1849–1945) designed the Poldhu transmitter and in 1904 invented the thermionic valve, or vacuum diode.
• George Kemp, Marconi’s long-serving assistant, was the only other person to hear the 1901 signal.
• Percy Paget helped build the Signal Hill station.

Consequences

After the experiment, the Anglo-American Telegraph Company, which held a telegraph monopoly in Newfoundland, threatened legal action, and Marconi moved his North American work to Glace Bay, Nova Scotia, with support from the Canadian government. Messages were exchanged across the Atlantic in December 1902, and in January 1903 a greeting from US President Theodore Roosevelt to King Edward VII was sent from Cape Cod. A regular commercial service between Glace Bay and Clifden in Ireland opened in October 1907.

Wireless transformed safety at sea. In 1910 a wireless message from the liner Montrose led to the arrest of the murderer Hawley Crippen. In April 1912 the distress calls of the Titanic’s Marconi operators brought the Carpathia to rescue survivors (see the sinking of the Titanic), and new laws soon required ships to keep a radio watch at all times.

Legacy and disputes

Marconi shared the 1909 Nobel Prize in Physics with the German physicist Karl Ferdinand Braun for contributions to wireless telegraphy. His priority remained contested: in 1943 the US Supreme Court ruled that key claims in his American patent on tuning were invalid because of earlier work by Lodge, Nikola Tesla and John Stone Stone. Historians generally see Marconi less as the sole inventor of radio than as the person who made it work over long distances and built an industry around it.

Later in life Marconi pioneered shortwave and microwave communication and became a prominent public figure in Mussolini’s Italy. When he died in Rome on 20 July 1937, radio stations in many countries fell silent for two minutes in his honour.

Timeline

• 1874, 25 April: Guglielmo Marconi is born in Bologna.
• 1887: Heinrich Hertz demonstrates radio waves.
• 1896, June: Marconi files his first British patent in London.
• 1897, July: Marconi founds his wireless company.
• 1901, 17 September: A gale destroys the original aerial at Poldhu.
• 1901, 12 December: Marconi reports receiving the letter S at Signal Hill.
• 1902, February: Shipboard tests on the Philadelphia confirm long-range reception.
• 1907, October: Regular transatlantic wireless service begins.
• 1909, December: Marconi shares the Nobel Prize in Physics with Karl Ferdinand Braun.
• 1937, 20 July: Marconi dies in Rome.

Why it matters

The Signal Hill experiment showed that radio waves could cross an ocean, defying expert opinion. It began the shift from cables to wireless that led to broadcasting, radar, satellite links and mobile phones, and it made instant communication with ships at sea a routine part of life.