A heliograph is a wireless solar telegraph that signals by flashes of sunlight reflected
by a mirror. The flashes are produced by momentarily pivoting the mirror, or by interrupting the
beam with a shutter. The heliograph was a simple but effective instrument for instantaneous
optical communication over long distances during the late 19th and early 20th century.
Its main uses were military, survey and forest protection work. Heliographs were standard
issue in the British and Australian armies until the 1960s, and were used by the Pakistani
army as late as 1975.
Description
There were many heliograph types. Most heliographs were variants of the British Army Mance Mark
V version. It used a mirror with a small unsilvered spot in the centre. The sender aligned the
heliograph to the target by looking at the reflected target in the mirror and moving
his head until the target was hidden by the unsilvered spot. Keeping his head still, he
then adjusted the aiming rod so its cross wires bisected the target. He then turned
up the sighting vane, which covered the cross wires with a diagram of a cross, and aligned
the mirror with the tangent and elevation screws so the small shadow that was the reflection
of the unsilvered spot hole was on the cross target. This indicated that the sunbeam was
pointing at the target. The flashes were produced by a keying mechanism that tilted the mirror
up a few degrees at the push of a lever at the back of the instrument. If the sun was
in front of the sender, its rays were reflected directly from this mirror to the receiving
station. If the sun was behind the sender, the sighting rod was replaced by a second
mirror, to capture the sunlight from the main mirror and reflect it to the receiving station.
The U. S. Signal Corps heliograph mirror did not tilt. This type produced flashes by a
shutter mounted on a second tripod. The heliograph had some great advantages.
It allowed long distance communication without a fixed infrastructure, though it could also
be linked to make a fixed network extending for hundreds of miles, as in the fort-to-fort
network used for the Geronimo campaign. It was very portable, did not require any power
source, and was relatively secure since it was invisible to those not near the axis of
operation, and the beam was very narrow, spreading only 50 feet per mile of range. 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. Conversely, the narrow beam made it very difficult to stay aligned
with a moving target, as when communicating from shore to a moving ship, and the British
issued a dispersing lens to broaden the heliograph beam from its natural diameter of 0.5 degrees
to 15 degrees for that purpose 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 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 apart on
September 17, 1894, with Signal Corps heliographs carrying mirrors only 8 inches square.
History
The German professor Carl Friedrich Gauss of the University of Göttingen developed
and used a predecessor of the heliograph in 1821. His device directed a controlled beam
of sunlight to a distant station to be used as a marker for geodetic survey work, and
was suggested as a means of telegraphic communications. This is the first reliably documented heliographic
device, despite much speculation about possible ancient incidents of sun-flash signalling,
and the documented existence of other forms of ancient optical telegraphy.
For example, one author in 1919 chose to "hazard the theory" that the mainland signals Roman
emperor Tiberius watched for from Capri were mirror flashes, but admitted "there are no
references in ancient writings to the use of signaling by mirrors", and that the documented
means of ancient long-range visual telecommunications was by beacon fires and beacon smoke, not
mirrors. Similarly, the story that a shield was used
as a heliograph at the Battle of Marathon is a modern myth, originating in the 1800s.
Herodotus never mentioned any flash. What Herodutus did write was that someone was accused
of having arranged to "hold up a shield as a signal". Suspicion grew in the 1900s that
the flash theory was implausible. The conclusion after testing the theory was "Nobody flashed
a shield at the Battle of Marathon". In a letter dated 3 June 1778, John Norris,
High Sheriff of Buckinghamshire, England, notes: "Did this day heliograph intelligence
from Dr [Benjamin] Franklin in Paris to Wycombe". However there is little evidence that "heliograph"
here is other than a misspelling of "holograph". The term "heliograph" for solar telegraphy
did not enter the English language until the 1870s - even the word "telegraphy" was not
coined until the 1790s. Sir Henry Christopher Mance, of the British
Army Signal Corps, developed the first widely accepted heliograph about 1869 while stationed
at Karachi, in the Bombay Presidency in British India. Mance was familiar with heliotropes
by their use for the Great India Survey. The Mance Heliograph was operated easily by one
man, and since it weighed about seven pounds, the operator could readily carry the device
and its tripod. The British Army tested the heliograph in India at a range of 35 miles
with favorable results. During the Jowaki Afridi expedition sent 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 more than 60 years. The usefulness of heliographs was limited to daytimes
with strong sunlight, but they were the most powerful type of visual signalling device
known. In pre-radio times heliography was often the only means of communication that
could span ranges of as much as 100 miles with a lightweight portable instrument.
In the United States military, by January 1880, Colonel Nelson A. Miles had established
a line of heliographs connecting Fort Keogh and Fort Custer, Montana, a distance of 140
miles. In 1890, Major W. J. Volkmar of the US Army, demonstrated in Arizona and New Mexico
the possibility of performing communication by heliograph over a heliograph network aggregating
2,000 miles in length. 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 1888, the US Signal Service reviewed all of these devices, as well as the Finley Helio-Telegraph,
and finding none completely suitable, developed the US Signal Service heliograph, a two-tripod,
shutter-based machine of 13 7/8 lb. total weight, and ordered 100 for a total cost of
$4,205. In 1893, the number of heliographs manufactured for the US Signal Service was
133. The heyday of the heliograph was probably
the Second Boer War in South Africa, where it was much used by both the British and the
Boers. The terrain and climate, as well as the nature of the campaign, made heliography
a 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. During 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 heliography 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 heliograph of the single-tripod,
shutter plus mirror type for forestry use. Immediately prior to the outbreak of World
War I, the cavalry regiments of the Russian Imperial Army were still being trained in
heliograph communications to augment the efficiency of their scouting and reporting roles. The
Red Army during the Russian Civil War made use of a series of heliograph stations to
disseminate intelligence efficiently about basmachi rebel movements in Turkestan in 1926.
During World War II, South African and Australian forces used the heliograph against German
forces in Libya and Egypt in 1941 and 1942. 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" type of communication. The Canadian Army was
the last major army to have the heliograph as an issue item. By the time the mirror instruments
were retired, they were seldom used for signalling. However, as recently as the 1980s, heliographs
were used by Afghan forces during the Soviet invasion of Afghanistan. Signal mirrors are
still included in survival kits for emergency signaling to search and rescue aircraft.
Heliographs in fiction Rudyard Kipling's humorous poem "A Code of
Morals" describes a fictional interception of a heliograph signal in 19th century India.
In the book The War of the Worlds by H. G. Wells, heliographs are used to convey information
about the invading Martians. The short story "The Attack on the Mountain"
by Glendon Swarthout, in The Saturday Evening Post, July 4, 1959, described the use of the
heliograph in the American West. The 2004 Western novel The Sergeant's Lady
by Miles Hood Swarthout is set against the background of the heliograph network used
in the U.S. Army campaign against the Apache Indians.
In the 2010 science fiction novel Terminal World by Alastair Reynolds, the faction of
people known as 'Swarm' use heliographs as communication between airships.
In Robert Penn Warren's All the King's Men, a heliograph serves as an important image
and appears early—on the second page of the novel.
In Agatha Christie's 1947 novel The Labours of Hercules from the short story "The Erymanthian
Boar" detective Hercule Poirot uses a heliograph to communicate from the top of Rochers Neiges
where he is trapped to the police at the mountain's base.
In Larry Niven's Ringworld series, revealed in The Ringworld Throne, the Ghoul species
use heliographs for their vast communication network across the Ringworld.
Also, in Larry Niven's book The Smoke Ring, the Admiralty Navy uses heliographs to communicate
with its rocket ships. In the role-playing game Space: 1889, the
Great Powers communicate with their colonial possessions on the inner planets of the Solar
System by means of "orbiting heliograph stations". In The Adventures of Tintin comic The Red
Sea Sharks, the US Navy communicates by heliograph to antagonist Rastapopoulos.
In the television series Lost, Benjamin Linus signals his people using a heliograph in the
episode "There's No Place Like Home". In the Agatha Christie novel And Then There
Were None Lombard suggests creating a heliograph to contact the mainland.
The books Matter and Feersum Endjinn by Iain M. Banks both feature several instances of
heliographic communication. The Realm, the central empire in the world
of the roleplaying game Exalted, possesses an elaborate heliograph network.
See also Heliotrope
Semaphore line Signal lamp
Telegraph hill Heliography, an early photographic process
invented by Joseph Nicéphore Niépce around 1822
References
Great Days of the Heliograph by Lewis Coe External links
Heliography: Communicating with Mirrors Photographs of British, American and Portuguese heliographs.
The Heliograph A description of the British Mance, Begbie and French LeSeurre heliographs
with illustrations Eliografo Detailed color photographs of a
World War 2 British Mance heliograph. "Heliograph" at the National Library of Australia:
Trove; 100+ historical heliograph photographs at the Australian War Memorial and elsewhere
Royal Signals Datasheet No. 2. The Heliograph CHAPTER IV THE HELIOGRAPH
Mance Mark V Heliograph Detailed photos of a British Mark V Heliograph and kit, links
to patents. Clicking on visible photos reveals high resolution photos.
The Heliograph in the Apache Wars Signals communication in the South African
War 1899-1902