Heliographs

__What is a heliograph?__

A **Heliograph** (from the [|Greek] //[|helios]// ([|Greek]: Ἥλιος), meaning "sun", and //[|graphein] (γραφειν)// = write) is a wireless solar [|telegraph] that signals using [|Morse code] 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 highly effective instrument for instantaneous [|optical communication] over 50 km or more in the late 19th and early 20th century. Its major 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.

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__When were heliographs invented?__ The ancient greeks used heliographs as long ago as 405 BC.

__Who invented more modern heliographs?__ 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. Sir Henry Christopher Mance (1840–1926), of British Army Signal Corps, developed the first heliograph apparatus.

__Where were more modern heliographs invented?__ England.

__How were heliographs used?__ The silver is removed from the center of the mirror, about 1/8" dia. The mirror is pivoted vertically and horizontally, and a pointer which has vertical adjustment is located as shown. Looking through the unsilvered spot as a peep-sight and over the pointer to the station to be contacted, the assembly is clamped. In line with the direction desired, set up the shutter as close to the pointer as practicable. The mirror is then adjusted until the reflected light is directed on the white shutter. When the shadow of the unsilvered spot appears just over the pointer, we know that the ray is centered on our target. Frequent adjustment of the mirror is essential, and the alignment must not be disturbed.

__ When should we use a heliograph message? __ We should use it in sunlight, depending on the atmosphere and size of the mirror, and when there are hardly any clouds. __Does it need to be sunny?__ Yes it does, because sunlight has a luminous efficiency. __Where should we signal?__ From high ground.

__What can we use to signal?__ A piece of metal or a mirror. A CD or a knife, a metal cup, sheet metal, a makeup mirror or a pair of glasses could be used.

__What were heliographs used for?__ To warn if enemies were coming, in case of danger, to signal for help. __What mirror is best? __ A mirror with a hole in the middle.

__How do we use it?__ The sender looked through this hole to align the tip of a sighting rod with the target. They then aligned the mirror so the small shadow that was the reflection of the sighting hole was on the tip of the sighting rod. This indicated that the sunbeam was pointing at the target.

__Why do we have to use the heliograph?__ It is a way to send messages anywhere, up to 100 km away.

__What code is used to send a heliograph message?__ Morse code. __Could we write our own heliograph code?__ Yes, if you learned to use it and know all of the answers above.