The heliograph had some powerful advantages. It allowed long distance communication without a fixed infrastructure, though it could also be linked to make a fixed network extending over hundreds of miles, as in the fort-to-fort network used in the Geronimo campaign. It was highly portable, required no power source, and was relatively secure since it was invisible to those not near the axis of operation. However, anyone in the beam with the correct knowledge could intercept signals without being detected. In the Boer war, where both sides used heliographs, tubes were sometimes used to decrease the dispersion of the beam.
The distance that heliograph signals could be seen depended on the clarity of the sky and the size of the mirrors used. A clear line of sight was required, and since the earth's surface is curved, the highest convenient points were used. Under ordinary conditions, a flash could be seen 30 miles (48 km) with the naked eye, and much farther with a telescope. The maximum range was considered to be 10 miles for each inch of mirror diameter. Mirrors ranged from 1.5 inches to 12 inches or more. The record distance was established by a detachment of U.S. signal sergeants by the inter-operation of stations on Mount Ellen, Utah, and Mount Uncompahgre, Colorado, 183 miles (295 km) apart on Sept 17, 1894, with Signal Corps heliographs carrying mirrors only 8 inches square.
The first recorded use of the heliograph was in 405 BC, when the Ancient Greeks used polished shields to signal in battle. In about 35 AD, the Roman emperor Tiberius, by then very unpopular, ruled his vast empire from a villa on the Isle of Capri. It is thought that he sent coded orders daily by heliograph to the mainland, eight miles away.
The German professor Carl Friedrich Gauss, of Georg-August University of Göttingen, outlined a first design for a predecessor of the heliograph (called heliotrope) in 1810. His device directed a controlled beam of sunlight to a distant station to serve as a marker for geodetic survey work.
Sir Henry Christopher Mance (1840–1926), of British Army Signal Corps, developed the first apparatus while stationed at Karachi, Bombay. Mance was familiar with heliotropes through their use in the Great India Survey.The Mance Heliograph was easily operated by one man, and since it weighed about seven pounds, the operator could readily carry the device and its tripod. During the Jowaki Afridi expedition sent out by the British-Indian government in 1877, the heliograph was first tested in war.
The simple and effective instrument that Mance invented was to be an important part of military communications for over 60 years. Although limited to use in sunlight, the heliograph was the most powerful visual signalling device known. In pre-radio days it was often the only means of communication that could span ranges of up to 100 miles with a lightweight portable instrument.
Major W. J. Volkman of the US Army, demonstrated in Arizona and New Mexico the possibility of carrying on communication by heliograph over a range of 200 miles. The network of communication begun by General Miles in 1886, and continued by Lieutenant W. A. Glassford, was perfected in 1889 at ranges of 85, 88, 95, and 125 miles over a rugged and broken country, which was the stronghold of the Apache and other hostile Indian tribes.
By 1887, heliographs in use included not only the British Mance and Begbie heliographs, but also the American Grugan, Garner and Pursell heliographs. The Grugan and Pursell heliographs used shutters, and the others used movable mirrors operated by a finger key. The Mance, Grugam and Pursell heliographs used two tripods, and the others one. The signals could either be momentary flashes, or momentary obscurations. In 1889 the U.S. Signal Service reviewed all of these devices, as well as the Finley Helio-Telegraph, and finding none completely suitable, developed the U.S. Signal Service heliograph, a two-tripod, shutter based machine of 13 7/8 lb. total weight, and ordered 100 for a total cost of $4205.
The heyday of the heliograph was probably the Boer War in South Africa, where it was heavily used by both the British and the Boers. The terrain and climate, as well as the nature of the campaign, made the heliograph the logical choice. For night communications, the British used some large Aldis lamps, brought inland on railroad cars, and equipped with leaf-type shutters for keying a beam of light into dots and dashes. In the early stages of the war, the British garrisons were besieged in Kimberley, Ladysmith, and Mafeking. With land telegraph lines cut, the only contact with the outside world was via light-beam communication, helio by day, and Aldis lamps at night.
In 1909, the use of the heliograph for forestry protection was introduced in the United States. By 1920 such use was widespread in the US and beginning in Canada, and the heliograph was regarded as "next to the telephone, the most useful communication device that is at present available for forest-protection services". D.P. Godwin of the US Forestry Service invented a very portable (4.5 lb) heliograph of the single-tripod, shutter plus mirror type for forestry use.
The heliograph remained standard equipment for military signallers in the Australian and British armies until the 1960s, where it was considered a "low probability of intercept" form of communication. Canada was the last major army to keep the heliograph as an issue item. By the time the mirror instruments were retired they were seldom used for signalling. Still, the army hated to see them go as, "They made damn fine shaving mirrors." As recently as the 1980s, heliographs were used by Afghan forces during the Soviet invasion of Afghanistan. They are still included in survival kits for emergency signalling to search and rescue aircraft.