stars. The wliolc apparatus was then mounted s(j 

 that it was free to revolve about its polar axis and 

 another ring or a casinf< was added, external and fixed, 

 to rejjrcsent the horizon that provided a datum for 

 the rising; and setting of the Sun and the stars. 



In the next stage, reached very .soon after this, the 

 rotation of ihe model was arranged to proceed auto- 

 matically instead of by hand. This was done, we be- 

 lieve, by using a slowly revolving wheel powered by 

 dripjiing water and tinning the tnodel through a re- 

 duction mechanism, probably inv'olving gears or, 

 more reasonably, a single large gear turned by a trip 

 lever. It did not matter much that the time-keeping 

 properties were poor in the long run; the model 

 moved "by itself" and the great wonder was that it 

 agreed with the observed heavens "like the two halves 

 of a tally." 



In the next, and essential, stage the turning ol the 

 water wheel was regulated by an "escapement"' 

 mechanism consisting of a weighbridge and trip 

 levers so arranged that the wheel was held in check, 

 scoop by scoop, while each scoop was tilled by the 

 dripping water, then released by the weighbridge 

 and allowed to rotate until checked again by the 

 trip-lever arrangement. Its action was similar to 

 that of the anchor escapement, though its period of 

 repose was much longer than its period of motion 

 and, of course, its timekeeping properties were con- 

 trolled not only bv the mechanics of the device but 

 also by the rate of flow of the dripping water. 



The Chinese escapement may justifiably be re- 

 garded as a missing link, just halfway between the 

 elementary clepsydra with its steady flow of water 

 and the mechanical escapement in which time is 

 coimted by chopping its flow into cycles of aciion, 

 repeated indefinitely and counted by a cumulating 

 device. W'ith its characteristic of saving up energy 

 for a considerable period (about 15 minutes) before 

 letting it go in one powerful action, the Chinese 

 escapement was particularly suited to the (lri\ing 

 of jackwork and other demonslraiion dc\ices recjuir- 

 ing much energy but only intermittent activity. 



In its final form, as built by Su Sung after many 

 trials and improvements, the Chinese '"astronomical 

 clock-tower" must ha\e been a most impressive 

 abject. It had the form of a tower about 30 feet 

 high, surmounted by an observation platform covered 

 with a light roof (see tig. 4). On the platform wa.< 

 an armillary sphere designed for observing the 

 heavens. It was turned by the clockwork so as to 

 follow the diurnal rotation and thus avoid the distress- 



ing compulations caused by the change of coordinates 

 necessary when fixed alt-azimuth instruments were 

 used. Below the platform was an enclosed chamlxT 

 containing the automatically rotated celestial giolx- 

 which so wonderfully agreed with the heavens. 

 Below this, on the front of the tower was a miniature 

 pagoda with five tiers; on each tier was a doorway 

 through which, at due moment, appeared jacks who 

 rang bells, clanged gongs, beat drums, and held 

 tablets to announce the arrival of each hour, each 

 quarter (they used 100 of them to the day) and each 

 watch of the night. Within the tower was concealed 

 the mechanism; it consisted mainly of a central 

 vertical shaft providing power for the sphere, glolje, 

 and jackwheels, and a horizontal shaft geared to the 

 vertical one and carrying the great water wheel 

 which seemed to set it.self magically in motion at 

 every quarter. In addition to all this were the levers 

 of the escapement mechanism and a pair of norias 

 by which, once each day, the water used was pumped 

 from a sump at the bottom to a reservoir at the top, 

 whence it descended to work the wheel by means of 

 a constant level tank and .several channels. 



There were many offshoots and developments of 

 this main stem of Chinese horology. We are told, 

 for example, that often mercury and occasionally 

 sand were used to replace the water, which frequently 

 froze in winter in sjjiie of the application of lighted 

 braziers to the interior of the machines. Then 

 again, the astronomical models and the jackwork 

 were themselves subject to gradual improvement: at 

 the time of I-Hsing, for example, special attention 

 was paid to the demarcation of ecliptic as well as 

 the normal equatorial coordinates; this was clearly 

 an influx from Hellenistic-Islamic astronomy, in 

 which the relatively sophisticated planetary mathe- 

 matics had forced this change not otherwise noted 

 in C:hina. 



By the time of the Jesuits, this current of Chinese 

 horology, long since utterly destroyed by the perils 

 of wars, storms, and governmental reforms, had quite 

 been forgotten. Matteo Ricci"s clocks, those gifts 

 that aroused so much more interest than European 

 theological teachings, were obviously something 

 quite new to the 16th-century Chinese scholars; so 

 much so that they were dubbed with a quite new 

 name, "'self-.sounding bells," a direct translation 

 of the word "clock" (glokke). In view of the fact 

 that the medieval Chinese escapement may have 

 been the basis of European horology, it is a curious 

 twist of fale that the high regard of the Chinese for 



PAPER 6: CLOCKWORK, PERPETLAL MOTION DEVICES, .AND THE COMP.\S,S 



87 



