Heliographs

For as long as there have been people, there has been a need to communicate quickly, especially over long distances. For most of human history, the only way to send messages from one town to the next or to relay orders and intelligence during times of war was on foot with runners or on horseback. This could be dangerous however, as runners could be killed or bribed and their messages intercepted.

What was needed was a way to communicate quickly over long distances. Many different methods of achieving this been tried over the years, but the most effective was the heliograph. A heliograph is a type of semaphore that harnesses a focused beam of sunlight and Morse code to communicate quickly over long distances. The first recorded mention of sunlight being used for communication is in Xenophon’s Hellenica where he describes how the ancient Greeks sometimes used sunlight reflected of off highly polished shields to indicate the positions of friendly troops and to relay orders during the Peloponnesian War.

The first patent for a modern heliograph was filed in 1810 by German mathematician Carl Friedrich Gauss. Gauss was a professor at Georg-August University in Gottingen, Germany who was looking to increase the speed and accuracy of geodesic surveys. The first wide spread use of the heliograph came in the mid-19^th Century. They were quickly adopted by the British and proved to be particularly effective in providing fast and reliable communications during Britain’s many colonial wars in Africa, India and the Middle East.

In his 1993 book, The Telegraph: A History of Morse’s Invention and it’s Predecessors in the United States, Lewis Coe wrote, “one of the most successful and widely used signalling systems, the Heliograph did not appear until after most visual signalling systems were considered obsolete.”

The British Army employed a single mirror model named for its designer, Sir Henry Christopher Mance. Mance became interested in using reflected sunlight to communicate while attending the British Army’s Signal School in the 1860s. The Mance heliograph employed a single mirror with a small sighting hole in the middle and attached crosshairs mounted on a tripod. Signals were sent through a telegraph key mounted on the back of the mirror, which tilted the mirror upwards when pressed and interrupted the beam of sunlight, causing the mirror to flash on and off. Auxiliary mirrors could also be used to redirect sunlight onto the signalling mirror if the sun was at the wrong angle or if the sunlight was too diffused.

In the United States a two mirror apparatus was used by the US Army and Cavalry Corp. A signalling mirror was mounted on a tripod in front of a second mirror which was set up on a second tripod a short distance away. Messages could be sent by opening and closing flaps positioned between the reflecting mirror and the signalling mirror. Heliographs figured prominently in the US Cavalry’s efforts to put down Geronimo’s Apache Rebellion in 1886.

Despite its apparent backwardness, the heliograph proved to a popular means of sending messages quickly where telegraph lines did not exist. In the right conditions, a message sent by heliograph could be visible up to 48 kilometres away and even farther than that by telescope. In September, 1897, the US Army set a record when it sent a message by heliograph from Mount Ellen, Utah to Mount Uncompahgre, Colorado, almost 300 kilometres away, using mirrors that measured only 8 inches square.

The last wide spread use of heliographs for communication was during the Boer War in South Africa, which lasted from 1899 to 1902. When the British garrisons at Kimberly, Ladysmith and Mafeking were surrounded and besieged by the Boers, the British relied on heliographs by day and signal lamps by night for rapid communication with the outside world. With the widespread implementation of radio technology in the early 20^th Century, however, interest in heliographs began to wane.

By 1935, heliographs ceased to be a principal means of battlefield communications. Even after the Second World War, however, heliographs remained popular among the special force branches of many of the world’s armies due to their portability, long range, low probability of detection, and ease of use. In the 1980s, Afghan Mujahedeen fighters were still using British patterned heliographs in their guerrilla war against the Soviet Union.