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A billiard ball is a small, hard ball used in cue sports, such as carom billiards, pool, and snooker. The number, type, diameter, color, and pattern of the balls differ depending upon the specific game being played. Various particular ball properties such as hardness, friction coefficient and resilience are important to accuracy. ==History== Early balls were made of various materials, including wood and clay (the latter remaining in use well into the 20th century). Although affordable ox-bone balls were in common use in Europe,〔Note: Antique ox-bone balls remain a very common item on eBay.〕 elephant ivory was favored since at least 1627 until the early 20th century; the earliest known written reference to ivory billiard balls is in the 1588 inventory of the Duke of Norfolk. By the mid-19th century, elephants were being slaughtered for their ivory at an alarming rate, just to keep up with the demand for high-end billiard balls – no more than eight balls could be made from a single elephant's tusks. The billiard industry realized that the supply of elephants (their primary source of ivory) was endangered, as well as dangerous to obtain (the latter an issue of notable public concern at the turn of the 19th century).〔 Inventors were challenged to come up with an alternative material that could be manufactured, with a US$10,000 prize being offered by a New York supplier,〔 Phelan and Collender. (This would be worth approximately $ today.) Although not the first artificial substance to be used for the balls (e.g. Sorel cement, invented in 1867, was marketed as an artificial ivory), John Wesley Hyatt invented a composition material in 1869 called nitrocellulose for billiard balls (US patent 50359, the first American patent for billiard balls). It is unclear if the cash prize was ever awarded, and there is no evidence suggesting he did in fact win it.〔〔 〕 By 1870 it was commercially branded Celluloid, the first industrial plastic. Unfortunately, the nature of celluloid made it volatile in production, occasionally exploding, which ultimately made this early plastic impractical.〔 Urban legend has it that celluloid billiard balls themselves would occasionally explode during rough play, but no reliable sources have been found that can substantiate this. Subsequently, to avoid the problem of celluloid instability, the industry experimented with various other synthetic materials for billiard balls such as Bakelite, Crystallite and other plastic compounds. The exacting requirements of the billiard ball are met today with balls cast from plastic materials that are strongly resistant to cracking and chipping. Currently Saluc, under the brand names Aramith〔(Aramith )〕 and Brunswick Centennial,〔(【引用サイトリンク】title=History )〕 manufactures phenolic resin balls. Other plastics and resins such as polyester (under various trade names) and clear acrylic are also used, by competing companies such as Elephant Balls Ltd.〔(Elephant Balls Ltd. )〕 and Frenzy Sports.〔(Frenzy Sports )〕 Ivory balls remained in use in artistic billiards competition until the late 20th century.〔 :''(See also Cue sports, "History" for more-general information on billiards history.)'' 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「Billiard ball」の詳細全文を読む スポンサード リンク
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