The lowest payment level goes to the Observers of the Sunrise and the Professors of the Clepsydras at five piculs per month.
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To accommodate the influx of new workers, the ranking system within the occupation also transitioned. There became one Director, supported by two Deputy Directors, followed by a Registrar with four seasonal Chiefs. Then came eight Chief Astronomers, five Chief Diviners, two Chiefs of the Clepsydras, and three Observers.
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One of four clock faces of Notre-Dame's 19th century clock (right). Chimes for the 18th century clock were once held in a turret similar to the one pictured left on the north transept. The first clocks used at Notre-Dame were clepsydras. These were used to tell the hours, which were marked by striking bells.
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Within the Bureau, payment was decided upon by rank. As established in the year 1392, the top rank of Directors is paid sixteen piculs of rice per month. The Deputy Directors and Chiefs of the Five Agencies are allotted ten piculs per month, the Astronomers receive seven piculs, while both the Registrars and Chief Diviners have six and a half piculs. The Chiefs of the Clepsydras receive six piculs, and the Calendar Officers and Observers both have five and a half piculs.
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In a famous fragment, Empedocles attempted to explain the phenomenon of respiration by means of an elaborate analogy with the clepsydra, an ancient device for conveying liquids from one vessel to another.Jonathan Barnes (2002), The Presocratic Philosophers, Routledge, p. 313.Carl Sagan (1980), Cosmos, Random House, pp. 179–80. This fragment has sometimes been connected to a passage in Aristotle's Physics where Aristotle refers to people who twisted wineskins and captured air in clepsydras to demonstrate that void does not exist.
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Aristotle, Physics, 213a24–7 There is however, no evidence that Empedocles performed any experiment with clepsydras. The fragment certainly implies that Empedocles knew about the corporeality of air, but he says nothing whatever about the void. The clepsydra was a common utensil and everyone who used it must have known, in some sense, that the invisible air could resist liquid.W. K. C. Guthrie, (1980), A history of Greek philosophy II: The Presocratic tradition from Parmenides to Democritus, Cambridge University Press, p. 224.
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In the 14th century Notre-Dame had two clepsydras running simultaneously, one in the cloister and one in the church itself. A lay chamberlain was responsible to keep the clocks filled with water and to notify a churchwarden when it was time to strike the bells for the hour. Such a job had to be ongoing 24 hours a day. In 1766, MM. Guillot de Montjoye and Jean-Bernard de Vienne, canons and members of Notre-Dame's factory counsel, donated a mechanical clock to the cathedral.
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Horology ("the study of time", related to Latin horologium from Greek , "instrument for telling the hour", from hṓra "hour; time" and -o- interfix and suffix -logy), . is the study of the measurement of time. Clocks, watches, clockwork, sundials, hourglasses, clepsydras, timers, time recorders, marine chronometers, and atomic clocks are all examples of instruments used to measure time. In current usage, horology refers mainly to the study of mechanical time-keeping devices, while chronometry more broadly includes electronic devices that have largely supplanted mechanical clocks for the best accuracy and precision in time-keeping.
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Sun and Moon, Nuremberg Chronicle, 1493 Many methods have been used to simulate mean solar time. The earliest were clepsydras or water clocks, used for almost four millennia from as early as the middle of the 2nd millennium BC until the early 2nd millennium. Before the middle of the 1st millennium BC, the water clocks were only adjusted to agree with the apparent solar day, thus were no better than the shadow cast by a gnomon (a vertical pole), except that they could be used at night. But it has long been known that the Sun moves eastward relative to the fixed stars along the ecliptic.
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Joseph Needham states that this was perhaps the ancestor of all clock jacks that would later sound the hours found in mechanical clocks by the 8th century, but he notes that these figures did not actually move like clock jack figurines or sound the hours. Many additional compensation tanks were added to later clepsydras in the tradition of Zhang Heng. In 610 the Sui Dynasty (581–618) engineers Geng Xun and Yuwen Kai crafted an unequal-armed steelyard balance able to make seasonal adjustments in the pressure head of the compensating tank, so that it could control the rate of water flow for different lengths of day and night during the year.Needham (1986), Volume 4, Part 2, 480.
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The Obelisk of Theodosius, detail of the pedestal: Theodosius I offers laurels of victory; we can see the water organ of Ctesibius, in the lower right-hand corner. The ancient Greek philosopher Plato (428–348 BC) was said to possess a large water clock with an unspecified alarm signal similar to the sound of a water organ; he used it at night, possibly for signaling the beginning of his lectures at dawn (Athenaeus 4.174c).; The Hellenistic engineer and inventor Ctesibius (fl. 285–222 BC) fitted his clepsydras with dial and pointer for indicating the time, and added elaborate "alarm systems, which could be made to drop pebbles on a gong, or blow trumpets (by forcing bell-jars down into water and taking the compressed air through a beating reed) at pre-set times" (Vitruv 11.11).
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