e 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, globe, and jackwheels,
and a horizontal shaft geared to the vertical one and carrying the great
water wheel which seemed to set itself 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
spite 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 mathematics had forced this change not otherwise
noted in China.

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 fate that the high regard of
the Chinese for European clocks should have prompted them to open their
doors, previously so carefully and for so long kept closed against the
foreign barbarians.

[Illustration: Figure 4.--ASTRONOMICAL CLOCK TOWER OF SU SUNG in
K'ai-feng, _ca._ A.D. 1090, from an original drawing by John
Christiansen. (_Courtesy of Cambridge University Press._)]

Mechanized Astronomical Models

Now that we have seen th