One of the oldest signal lights flashed out messages of impending attack by a powerful searchlight light beam atop the ancient lighthouse at Alexandria, Egypt before, in 1892, an electric carbon arc searchlight was used for an entirely different purpose—to forecast the weather.
Speaking of the Pharos Lighthouse, "which has no equal on the face of the earth," the medieval Arab geographer Al Bakri claimed the Alexandrians of ancient Egypt "assigned to its summit the celebrated mirror, which was made from a mixture of remarkable and extraordinary substances; they were able to see by it enemy ships on their way towards Alexandria, several days away, to prepare themselves for defense." Beside the mirror's function as a telescope, which was obviously used also to study the stars, it was used as a heliostat in sunlight; and at its center, the brilliant arc-light fire flashed out warnings on cloudy days and at night. “That the Pharos was used as a signal-station as well as a lighthouse is certain,” wrote Dr. A. J. Butler, “and at the time of the Arab conquest it was in full working order and flashed the sun by day and its own fire by night many leagues over the sea.” He went on to claim in his exhaustive work titled The Arab Conquest of Egypt and the Last Thirty Years of Roman Dominion that it was a “conspicuous landmark visible by day and by night at a distance of sixty or seventy miles.”
And, like the reflector atop the Pharos, the electric mirror on a much more modern tower was also seen a long ways off. In Men and Volts, The Story of General Electric, John Winthrop Hammond pointed out that
“People living in western Massachusetts noticed during that summer of 1892 a long shaft of light sweeping the night sky from somewhere in the White Mountains. The news quickly got about among the rural communities: an electric searchlight surmounted the summit of Mt. Washington. It was the largest unit of the sort then known.
An illustration of the huge searchlight mounted atop a tower on Mt. Washington
“To get the searchlight in place was a task to daunt the most determined engineer. A tower fifty-five feet high was to be built, and it was recorded that gales of over a hundred miles an hour swept that rugged peak. The Superintendent of the Mount Washington Inclined Railway wagered the construction man a silk hat for each one of his thirteen workmen that the tower would not last a year. He lost the bet, but never paid it.”
The weather searchlight on a tower atop Mt. Washington, N. H.
The Saturday, June 24, 1893 issue of Chambers’s Journal of Popular Literature, Science, and Art reported:
“Weather forecasts are being promulgated in New England in an altogether novel manner. On the summit of Mount Washington, an electric search-light is placed, and flashes its warnings over the surrounding country, the signals being well seen at a distance of eighty miles. From Boston the local forecast official sends out daily three hundred printed copies of weather forecasts for the next twenty-four hours. These go by rail, and are dropped at the various stations en route. At these stations the forecasts are immediately displayed, each in a frame provided by the Weather Bureau. It is found that this is the quickest method of bringing the forecasts under the notice of the public.”
An Army detachment of the Signal Corps posing in Cuba with their helio-lamp used for signaling during the Spanish-American War of 1898
The last half of the nineteenth century found a great increase in the use of bright lights, such as the carbon arc searchlights on naval vessels and army helio-lamps on tripods like the one illustrated above, for military signaling purposes. And perhaps this is from where the idea for the weather light on Mt. Washington arose.
A Serbian electric carbon arc searchlight fitted with a shutter for nighttime and daylight signaling
The weathermen probably flashed out their weather forecasts in Morse Code, by slowly turning the light of the searchlight on and off for specific periods by opening and closing a shutter in front of the light. However, a faster method of utilizing highly directional light for communications, by modulating ones voice upon its beams, was developed some years later. An article titled “Transmitting speech by light beams,” in a large volume titled Modern Inventions and Great Discoveries, published about 1915, gives us the following report on its development:
“Experiments in the transmission of speech by means of light beams were first made by Professor Bell some time ago with an apparatus called the ‘Photophone.’ The transmitter consisted of a plain mirror so arranged as to reflect the light upon a selenium cell in circuit with an ordinary receiver at the opposite station. The mirror served as a telephone diaphragm, a resonating chamber and mouthpiece being placed at the back. Speaking in the mouthpiece vibrated the mirror, the vibration altering the intensity of the beam of light. The changes in the light beam resulted in the selenium cell (acting with its well-known property of altering its electrical resistance under influence of light) setting up corresponding changes in the receiver circuit, and so producing vibrations in the receiver diaphragm like those communicated to the mirror of the transmitter. Professor Ruhmen, of Berlin, has improved somewhat on Bell’s device, but the same principle is retained and the system is successfully used on warships of the German navy.”
The Photophone being employed for communication with a naval vessel
Such a simple device was probably not beyond the know-how of the priestly technicians who maintained the electric light on the Pharos tower.
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