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The verge (or crown wheel) escapement is the earliest known type of mechanical escapement, the mechanism in a mechanical clock that controls its rate by allowing the gear train to advance at regular intervals or 'ticks'. Its origin is unknown. Verge escapements were used from the 14th century until the mid 19th century in clocks and pocketwatches. The name verge comes from the Latin ''virga'', meaning stick or rod. Its invention is important in the history of technology, because it made possible the development of all-mechanical clocks. This caused a shift from measuring time by continuous processes, such as the flow of liquid in water clocks, to repetitive, oscillatory processes, such as the swing of pendulums, which had the potential to be more accurate.〔, p.31〕 Oscillating timekeepers are used in all modern timepieces. ==Verge and foliot clocks== The verge escapement dates from 13th-century Europe, where its invention led to the development of the first all-mechanical clocks.〔 Starting in the 13th century, large tower clocks were built in European town squares, cathedrals, and monasteries. They kept time by using the verge escapement to drive a horizontal bar with weights on the ends called the foliot, a primitive type of balance wheel, to oscillate back and forth. The rate of the clock could be adjusted by sliding the weights in or out on the foliot bar. The verge probably evolved from the ''alarum'', which used the same mechanism to ring a bell and had appeared centuries earlier.〔, p.103-104〕 There has been speculation that Villard de Honnecourt invented the verge escapement in 1237 with an illustration of a strange mechanism to turn an angel statue to follow the sun with its finger,〔MS. 19093, folio 44, French Collection, Bibliothèque Nationale, Paris (No. 1104 Library of Saint-Germain-des Prés until c.1800). ( Villard_de_Honnecourt_-_Sketchbook_-_44.jpg ) is an image of the page on Wikimedia Commons〕 but the consensus is that this was not an escapement.〔, footnote 7〕〔, footnote 3〕 It is believed that sometime in the late 13th century the verge escapement mechanism was applied to tower clocks, creating the first mechanical clock. In spite of the fact that these clocks were celebrated objects of civic pride which were written about at the time, it may never be known when the new escapement was first used. This is because it has proven impossible to distinguish from the meager written documentation which of these early tower clocks were mechanical, and which were water clocks.〔White 1966, p.124〕 The same Latin word, ''horologe'', was used for both. Sources differ on which was the first clock 'known' to be mechanical, depending on which manuscript evidence they regard as conclusive. One candidate is the Dunstable Priory clock in Bedfordshire, England built in 1283, because accounts say it was installed above the rood screen, where it would be difficult to replenish the water needed for a water clock. Another is the clock built at the Palace of the Visconti, Milan, Italy, in 1335.〔, p.196〕 However, there is agreement that mechanical clocks existed by the late 13th century.〔〔〔(Whitrow 1989, p.104 )〕 The earliest description of an escapement, in Richard of Wallingford's 1327 manuscript ''Tractatus Horologii Astronomici'' on the clock he built at the Abbey of St. Albans, was not a verge, but a variation called a 'strob' escapement. It consisted of a pair of escape wheels on the same axle, with alternating radial teeth. The verge rod was suspended between them, with a short crosspiece that rotated first in one direction and then the other as the staggered teeth pushed past. Although no other example is known, it is possible that this design preceded the verge in clocks.〔 For the first two hundred years or so of the clock's existence, the verge was the only escapement used in mechanical clocks. In the sixteenth century alternative escapements started to appear, but the verge remained the most used escapement for 350 years until mid-17th century advances in mechanics, which also resulted in the invention of the pendulum. 〔 〕 Since clocks were valuable, after the invention of the pendulum many verge clocks were rebuilt to use this more accurate timekeeping technology, so very few of the early ''verge and foliot'' clocks have survived unaltered to the present day. How accurate the first verge and foliot clocks were is debatable, with estimates of one to two hours error per day being mentioned, although more recent evidence based sources mention achievable accuracies of minutes per day.〔W. Houtkooper “The Accuracy of the Foliot” Antiquarian Horology Vol. 20 No. One, Spring 1992〕〔M. Maltin “Some notes on the Medieval Clock in Salisbury Cathedral” Antiquarian Horology Vol. 20 No. 5, Spring 1993〕 Early verge clocks were probably no more accurate than the previous water clocks, but they did not freeze in winter and were a more promising technology for innovation. By the mid-17th century, when the pendulum replaced the foliot, the best verge and foliot clocks had achieved an accuracy of 15 minutes per day. 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「verge escapement」の詳細全文を読む スポンサード リンク
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