In his campaign to capture Geronimo in Arizona in 1886, Gen. Nelson Miles employed a device he had experimented with some success in Montana when he was commander of the Department of Missouri: the heliograph. The heliograph is a device made of a mirror, or pair of mirrors, that can be used to direct the sun?s light in a series of flashes to a distant receiving station, up to 100 miles away. The flashes are regulated either by tilting the mirror slightly (British Mance system), or by placing a shutter assembly in front of the mirror (U.S. system). See the photos both below. In either case, the mirror is tilted, or the shutter operated by a lever, much like a telegraph key, so that Morse Code, or prearranged code, may be sent. The estimated range of a heliograph is approximately 10 miles per inch of mirror size. The most common sizes were 5-inch, and 10-inch, with the 5-inch being easily transportable, and the 10-inch used in more permanent stations. In 1896, the U.S. Signal Corps established a distance record of transmitting a message 183 miles through the thin, clear desert air, using 8-inch mirrors and demonstrated sending a message over 800 miles in 4 hours, all without telegraphs or wires. Good operators could send and receive about 12-15 words per minute.
General Miles set up at network of 27 heliograph stations across an 800-mile stretch of the territory of western New Mexico and eastern Arizona, with its headquarters at Fort Bowie (halfway between Tombstone and Lordsburg AZ). See the map below. He was equipped with British-supplied Mance heliographs, as the U.S. had yet to design or manufacture their own. These heliograph stations were manned by a team of two or three operators of the Signal Corps, along with a detail of 5-10 soldiers for security. They were stationed at various mountain peaks in the area, with supplies and rations for 30 days. They were to maintain a lookout for movements by the Apache and send and/or relay any reports by heliograph to headquarters or another relay station. Although the use of the heliograph did not result in any significant tactical or decisive actions to capture Geronimo, its use did allow Miles to utilize his troops to the best effectiveness, without sending scouting parties to investigate every suspicious dust cloud. After his surrender, Gernoimo explained that his decision to surrender when he did was in part because "Miles' talking mirrors" could see and report all his movements, and that his capture and surrender was inevitable.
The success of the heliograph in Arizona resulted in the U.S. developing its own model, in 1887, which was used quite widely by the Army Navy in the Spanish-American War, and to a smaller extent in World War I. The British used the Mance heliograph extensively in India, Africa, and the 2nd Boer War, until the 1960?s. During the 118-day siege of Ladysmith, Natal (Nov 1899-Feb 1900) it was the only form of communication LtGen White had with the relief forces of Gen Buller. The advent of wireless telegraphy and radio replaced the heliograph in regular use, but its use and operation was still taught and utilized in other countries around the world, as late as the 1980?s (Afghanistan)
Pictures :
Top: British Mance Heliograph MkV
Middle: U.S. Heliograph, Model 1887
Bottom: Map of Gen Miles' Heliograph Network