Al-Jazari’s Castle Water Clock: Analysis of its Components and Functioning - IV
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4. Servicing and Maintenance
4.1. The Servants Job for the Day Ahead
This clock would not be possible without regular maintenance, and daily set up of all the parts mentioned so far. The servant must first ensure that half a days worth of water is in the reservoir, and this is crucial for the setting up of the spheres of the zodiac. The servant must take a strong cord and tie it to the nail for the sphere's pulley. With the zodiac positioned from the previous day, the nail is placed firmly into the hole of the pulley that corresponds to the sign that is rising from the horizon of the clock. For example, from the previous day, Aries was just about to rise from the horizon, the nail would be placed at the first point of Aries. The cord would then be wound once around the pulley and attached to a ring on the pulley directly below, i.e. the pulley for the crescent moon.
Going back to the example with Aries just about to rise from the horizon, the servant must next set the sun sphere so that it is opposite to the first point of Aries. This is done by having a firm grip of the iron bars, and turning the sun sphere by its handle. The moon is then set to the degrees of Taurus, which is the sign just after Aries. The ring with twenty-eight holes is rotated round so that the blank is behind the moon roundel. This will prevent observers from noticing the moon roundel during the day, and will rotate with the moon.
With the example of Aries, the flow regulator would be set to the point of Aries, and this would ensure that water would flow such that the hours of sun and night correspond to that particular day of the year.
Now that the zodiac, sun, moon spheres, and flow regulator are now set ready for the day ahead, the rest of the components within the clock are now placed back to their starting positions. Therefore the servant must now ensure the following:
a. The plate is directing it's pipe to the first of three sections in the valve trough;
b. all figures are suspended on their hooks;
c. the lower doors are positioned so that the heavier end is at the top and held in place by the catch;
d. the cart and crescent moon are at the left of the clock while looking from the front;
e. the string connecting the plugs in the valve trough to the sixth and ninth doors are lifted through the angle of the cross-pipe, and the twelfth door string connects directly to the plug in the last section of the valve trough;
f. lead balls are placed in every each slot, and all the blades are in their slits.
Al-Jazari describes what should be done during the beginning of the day at sunrise .
4.2. The Servants Job for the Night Ahead
All the water from the reservoir should now be in the cistern, and all the lead balls collected in a container on the floor of the house. The servant must now take the water from the cistern and pour it back into the main reservoir, and the water passed through a strainer at the top. No lead balls are placed back into their slots, so the falcons will serve little purpose during the night. The cross-pipe of the plate is rotated back so that it will deposit water into the first of the valve trough partitions. The sixth door figure will be hung up, but this time the weight behind to release the plug for the musicians to play will not be hung up with it. Instead this weight is hung up with the ninth door figure, and its string is passed through the angle of the pipe. The weight for the plug in the second trough is now placed and hung up with the twelfth figure door, but its string is not passed through the angle of the pipe.
|Figure 11: Schematic chart of the castle clock.|
The servant must now put the crescent moon/cart back to its original position on the left of the clock, if looking from the front. The moon roundel must be put on to its degree for that night, and its backing ring is rotated until the appropriate moon shape is behind the roundel. The sun disc is not moved. Going back to the example with Aries, the nail from the sphere's pulley must now be placed into the hole corresponding to the first point of Libra. The glass roundels for the hours of night should be covered, so that the crescent disc has its solid part uppermost behind the roundels.
Two lamps are now lit and placed inside the clock such that the light is spread throughout the clock. Al-Jazari describes their placing one on the left and the other on the right, so to spread light over the iron bows of the spheres. This was all the servicing that was required for the night ahead.
To conclude the description of how this clock works, a schematic chart of the clock and its components is given in Figure 11:
 Al-Jazari, The Book of Knowledge of Ingenious Mechanical Devices, op. cit., p. 40.
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by: Prof. Salim T. S. Al-Hassani, Thu 13 March, 2008