Previous flow regulators were all inaccurate...

Previous flow regulators were all inaccurate, but al-Jazari describes how he calibrated the instrument accurately by painstaking trial-and-error methods. Another type of clock, which may have been al-Jazari’s own invention, incorporates a closed-loop system: the clock worked as long as it was kept loaded with metal balls with which to strike a gong. Candle Clocks Al-Jazari also describes candle clocks, which all worked on a similar principle.

Each design specified a large candle of uniform cross-section and known weight (they even laid down the weight of the wick). The candle was installed inside a metal sheath, to which a cap was fitted. The cap was made absolutely flat by turning it on a lathe; it had a hole in the centre, around which, on the upper side, was an indentation. The candle, whose rate of burning was known, bore against the underside of the cap, and its wick passed through the hole.

Wax was collected in the indentation and could be removed periodically so that it did not interfere with steady burning. The bottom of the candle rested in a shallow dish that had a ring on its side connected through pulleys to a counterweight. As the candle burned away, the weight pushed it upward at a constant speed. The automata were operated from the dish at the bottom of the candle. No other candle clocks of this sophistication are known.

Miscellaneous Other chapters of al-Jazari’s work described fountains and musical automata, which are of interest mainly because in them the flow of water alternated from one large tank to another at hourly or half-hourly intervals. Several ingenious devices for hydraulic switching were used to achieve this operation. Mechanical controls are also described in chapters dealing with a potpourri of devices, including a large metal door, a combination lock and a lock with four bolts.

We see for the first time in al-Jazari’s work several concepts important for both design and construction: The lamination of timber to minimise warping, the static balancing of wheels, the use of wooden templates (a kind of pattern), the use of paper models to establish designs, the calibration of orifices, the grinding of the seats and plugs of valves together with emery powder to obtain a watertight fit, and the casting of metals in closed mould boxes with sand.

Conclusions Previously, how Islamic mechanical technology entered Europe is unknown.