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拍品专文
The equation of time results from the 23 degree tilt of the Earth's rotational axis and the fact that the Earth moves around the Sun in an elliptical orbit. For these two reasons, a "true" solar day, which is the interval of time between two "true" noons when the sun is at its highest point in the sky, is never the same length over the course of the year. It is exactly twenty-four hours long on just four days: 15 April, 14 June, 1 September and 24 December. In an unchanging cycle, all other days are either longer or shorter. This difference, which ranges from less 16 minutes and 23 seconds on 4 November to plus 14 minutes and 22 seconds on 11 February, is the "equation of time".
The display of the equation of time has always been one of the rarest if not the rarest of all watchmaking complications. Only the most sophisticated watches and clocks were fitted with the equation of time display, used to measure the difference between the length of the solar day, which constantly varies over the course of a year, and the length of the standard 24 hour civil day.
The most common indication is by means of a subsidiary dial or arc, graduated from -16 to +14 minutes, requiring some mental arithmetic by the wearer by adding or subtracting the relevant difference from mean time.
The accomplishment of the "equation running" display required the invention of another mechanical marvel. By means of extremely precise calculations based on the irregular path of the earth around the sun, watchmakers have developed a cam shaped like the figure-8 path made by the sun in the sky called "analemma", thus mechanically mimicking the curve derived by astronomers. Turning once per year, this cam is used to drive a finger producing a plus/minus display of the difference between solar time and civil time.
The first of the two minute hands indicates civil time in a conventional fashion. The second minute hand, decorated with the symbol of a golden sun, shows the solar time. Over the course of a year, the equation of time hand slowly overtakes and then slowly falls behind the minute hand as the sun overhead gradually catches up with and then falls behind civil time. This allows the user of the watch to directly read at a glance both civil time and solar time, as well as visualize the ever-changing relationship between the two. It is interesting to note that the first wristwatch fitted with the "running equation" display was launched only in 2004, further emphasizing the rarity of this system.
The rarest and most exclusive version is the equation of time display showing both solar time and civil time on the same dial by means of two co-axial minute hands. In the entire history of watchmaking, only an infinitesimal number of the world's most important clocks and watches were fitted with this exceedingly rare indication, also known as "équation marchante" or "running equation" display. In fact due to their utter exclusivity, nearly every "équation marchante" watch or clock made during the last two centuries has been recorded as historically significant timepiece.
The display of the equation of time has always been one of the rarest if not the rarest of all watchmaking complications. Only the most sophisticated watches and clocks were fitted with the equation of time display, used to measure the difference between the length of the solar day, which constantly varies over the course of a year, and the length of the standard 24 hour civil day.
The most common indication is by means of a subsidiary dial or arc, graduated from -16 to +14 minutes, requiring some mental arithmetic by the wearer by adding or subtracting the relevant difference from mean time.
The accomplishment of the "equation running" display required the invention of another mechanical marvel. By means of extremely precise calculations based on the irregular path of the earth around the sun, watchmakers have developed a cam shaped like the figure-8 path made by the sun in the sky called "analemma", thus mechanically mimicking the curve derived by astronomers. Turning once per year, this cam is used to drive a finger producing a plus/minus display of the difference between solar time and civil time.
The first of the two minute hands indicates civil time in a conventional fashion. The second minute hand, decorated with the symbol of a golden sun, shows the solar time. Over the course of a year, the equation of time hand slowly overtakes and then slowly falls behind the minute hand as the sun overhead gradually catches up with and then falls behind civil time. This allows the user of the watch to directly read at a glance both civil time and solar time, as well as visualize the ever-changing relationship between the two. It is interesting to note that the first wristwatch fitted with the "running equation" display was launched only in 2004, further emphasizing the rarity of this system.
The rarest and most exclusive version is the equation of time display showing both solar time and civil time on the same dial by means of two co-axial minute hands. In the entire history of watchmaking, only an infinitesimal number of the world's most important clocks and watches were fitted with this exceedingly rare indication, also known as "équation marchante" or "running equation" display. In fact due to their utter exclusivity, nearly every "équation marchante" watch or clock made during the last two centuries has been recorded as historically significant timepiece.