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SOS is the international Morse code distress signal (· · · – – – · · ·). This distress signal was first adopted by the German government in radio regulations effective April 1, 1905, and became the worldwide standard under the second International Radiotelegraphic Convention, which was signed on November 3, 1906, and became effective on July 1, 1908. SOS remained the maritime radio distress signal until 1999, when it was replaced by the Global Maritime Distress and Safety System.〔(【引用サイトリンク】accessdate = 2008-07-02 )〕 SOS is still recognized as a visual distress signal.〔(US Coast Guard Visual Distress Signals )〕 The SOS distress signal is a continuous sequence of three dits, three dahs, and three dits, all run together without letter spacing. In International Morse Code, three dits form the letter ''S'', and three dahs make the letter ''O'', so "SOS" became an easy way to remember the order of the dits and dahs. In modern terminology, SOS is a Morse "procedural signal" or "prosign", and the formal way to write it is with a bar above the letters: SOS. In popular usage, SOS became associated with such phrases as "''Save Our Ship''" or "''Save Our Souls''" or "''Send Out Succour"''. SOS is only one of several ways that the combination could have been written; VTB, for example, would produce exactly the same sound, but SOS was chosen to describe this combination. SOS is the only nine-element signal in Morse code, making it more easily recognizable, as no other symbol uses more than eight elements. ==Formalization== The use of the SOS signal was first introduced in Germany as part of a set of national radio regulations, effective April 1, 1905. These regulations introduced three new Morse code sequences, including the SOS distress signal. In 1906, at the second International Radiotelegraphic Convention in Berlin, an extensive collection of Service Regulations was developed to supplement the main agreement, which was signed on November 3, 1906, becoming effective on July 1, 1908. Article XVI of the regulations adopted Germany's ''Notzeichen'' (distress signal) as the international standard, reading: "Ships in distress shall use the following signal: · · · – – – · · · repeated at brief intervals". The first ship to transmit an SOS distress call appears to have been either the Cunard liner on June 10, 1909, according to "Notable Achievements of Wireless" in the September, 1910 ''Modern Electrics'', or the steamer SS ''Arapahoe'' on August 11, 1909. The signal of the ''Arapahoe'' was received by the United Wireless Telegraph Company station at Hatteras, North Carolina, and forwarded to the steamer company's offices. However, there was some resistance among the Marconi operators to the adoption of the new signal, and, as late as the April 1912 sinking of the , the ship's Marconi operators intermixed CQD and SOS distress calls. However, in the interests of consistency and water safety, the use of CQD appears to have died out thereafter. In both the April 1, 1905, German law, and the 1906 International regulations, the distress signal was specified as a continuous Morse code sequence of three-dits/three-dahs/three-dits, with no mention of any alphabetic equivalents. However, in International Morse, three dits comprise the letter S, and three dahs the letter O. It therefore soon became common to refer to the distress signal as "SOS". An early report on "The International Radio-Telegraphic Convention" in the January 12, 1907, ''Electrical World'' stated that "Vessels in distress use the special signal, SOS, repeated at short intervals." (In American Morse code, which was used by many coastal ships in the United States through the first part of the twentieth century, three dahs stood for the numeral "5", so in a few cases the distress signal was informally referred to as "S5S"). In contrast to CQD, which was sent as three separate letters with spaces between each letter, the SOS distress call has always been transmitted as a continuous sequence of ''dits'' and ''dahs'', and not as individual letters. There was no problem as long as operators were aware that "SOS" was technically just a convenient way for remembering the proper sequence of the distress signal's total of nine dits and dahs. In later years, the number of special Morse symbols increased. In order to designate the proper sequence of dits and dahs for a long special symbol, the standard practice is to list alphabetic characters that contain the same dits and dahs in the same order, with a bar atop the character sequence to indicate that there should not be any internal spaces in the transmission. Thus, under the modern notation, the distress signal becomes SOS. (In International Morse Code, VTB, IJS, VGI, and SMB, among others, would also correctly translate into the · · · – – – · · · distress call sequence, but traditionally only SOS is used). It has also sometimes been used as a visual distress signal, consisting of three short, three long, and three more short flashes of light, such as from a survival mirror, or with "SOS" spelled out in individual letters (for example, stamped in a snowbank or formed out of logs on a beach). The fact that SOS can be read right side up as well as upside down (as an ambigram) became important for visual recognition if viewed from above. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「SOS」の詳細全文を読む スポンサード リンク
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