Theory of international relations.
It is not necessary to study the internal politics of nations or governments, since their interactions on the international scene can be understood in terms of the pressures they exercise upon each other, and the responses to those pressures.
An application to international politics of behavioralism.
Graham Evans and Jeffrey Newnham, The Dictionary of World Politics (Hemel Hempstead, 1990)
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, elephant ivory was favored since at least 1627 until the early 20th century;:17 the earliest known written reference to ivory billiard balls is in the 1588 inventory of the Duke of Norfolk. Dyed and numbered balls appeared around the early 1770s.:17 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).:17 Inventors were challenged to come up with an alternative material that could be manufactured, with a US$10,000 (worth approximately $192,075 in 2021.) prize being offered by a New York supplier,l.:17
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.:17 By 1870 it was commercially branded Celluloid, the first industrial plastic. However, the nature of celluloid made it volatile in production, occasionally exploding, which ultimately made this early plastic impractical.:17 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 and Brunswick Centennial, manufactures phenolic resin balls. Other plastics and resins such as polyester (similar to those used for bowling balls) and clear acrylic are also used.
Ivory balls remained in use in artistic billiards competition until the late 20th century.:17
In the realm of carom billiards (or carambole) games, three balls are used to play most games on pocketless billiards tables. Carom balls are not numbered, and are 61–61.5 mm (between approximately 2 3⁄8 and 2 7⁄16 in) in diameter. They are typically colored as follows:
- White for player 1
- White with a spot (or yellow) cue ball for player 2
- Red (occasionally blue) (four-ball uses an extra object ball.)
|•||, white or off-white (sometimes with one or more spots)|
Pool balls are used to play various pool games, such as eight-ball, nine-ball and straight pool. These balls, the most widely used throughout the world, are smaller than carom billiards balls, slightly larger than British-style pool balls and substantially larger than those for snooker. According to World Pool-Billiard Association equipment specifications, the weight may be from 5 1⁄2 to 6.0 oz (160–170 g) with a diameter of 2 1⁄4 in (57 mm), plus or minus 0.005 in (0.127 mm). The balls are numbered and colored as in the table.
Balls 1 through 7 are often referred to asand 9 through 15 as , though there are many other colloquial terms for each of balls (highs and lows, etc.). Striped balls were introduced around 1889.:246 Though it looks similar to the solids, the 8 ball is not considered a solid because it is the only ball that is black. Some games such as nine-ball do not distinguish between stripes and solids, but rather use the numbering on the balls to determine which must be pocketed. In other games such as three-ball and straight pool neither type of marking is of any consequence. In eight-ball, straight pool, and related games, all sixteen balls are employed. In the games of seven-ball, nine-ball, and ten-ball, only object balls 1 through 7, 9, or 10, respectively (plus the cue ball) are used.
Some balls used in televised pool games are colored differently in order to make them more distinguishable on television monitors. Most commonly, the dark violet used on the 4 and 12 balls is replaced by pink to make it easier to distinguish the 4 from the black 8 ball, and similarly the 7 and 15 balls use a light tan color instead of a deep maroon. Other, less common color substitutions are also found, dependent on manufacturer. These sets often have a cue ball with multiple spots on its surface so thatplaced on it is evident to viewers.
Coin-operated pool tables, such as those found at bowling alleys, arcades, or bars, may use a slightly different-sized cue ball, so that the cue ball can be separated from object balls by the table’s ball return mechanism and delivered into its own ball return. Such different sized cue balls are considered less than ideal because they change the dynamics of the equipment. Other tables use a system where a magnet pulls a cue ball with a thin layer of metal embedded inside away from the object ball collection chamber and into the cue ball return, allowing the cue ball to more closely match the object balls in size and weight. More recently, optical systems that recognize the cue ball, which is more translucent than the other balls due to its solid white color, and separate it mechanically have been developed.
In WPA blackball pool (and its predecessor, WEPF English eight-ball pool) fifteen object balls again are used, but fall into two unnumbered 2 1⁄8 in (54 mm). The yellow-and-red sets are sometimes referred to as “casino sets” as they were formerly used for televised eight-ball championships,:45 most often held in casinos. The use of such sets, however, predates television, as they were sold by the Brunswick–Balke–Collender Co. as early as 1908.:24 Similar to standard pool balls, there are also special sets designed for televised games; these sets have a black-striped 8 ball, and a spotted cue ball., the (or less commonly ) and , with a white cue ball, and black 8 ball. Aside from the 8, shots are not since there is no reliable way to identify particular balls to be pocketed. Because they are unnumbered, they are wholly unsuited to certain pool games, such as nine-ball, in which ball order is important. They are typically smaller than the American-style balls. Neither the WPA nor the WEPF publicly define ball or table dimensions. The most common object ball diameters are 2 in (51 mm) and
Ball sets for snooker consist of twenty-two balls in total, arranged as a rack of 15 unmarked reds, sixplaced at various predetermined spots on the table, and a white cue ball. The colour balls are sometimes numbered with their point values in the style of pool balls for the home market.
Snooker balls are technically standardized at 52.5 mm (2.07 in) in diameter within a tolerance of plus or minus 0.05 mm (0.002 in). No standard weight is defined, but all balls in the set must be the same weight within a tolerance of 3 g (0.11 oz). However, many sets are actually 2 1⁄16 in (52.4 mm), even from major manufacturers. Snooker sets are also available with considerably smaller-than-regulation balls (and even with ten instead of fifteen reds) for play on smaller tables (down to half-size), and are sanctioned for use in some amateur leagues. Sets for American snooker are typically 2 1⁄8 in (54.0 mm), with numbered colour balls.