608 MODES OF KEEPING TIME KNOWN AMONG THE CHINESE. 
In some this was reversed, the float being made to mark time by its fall. 
A portable one was sometimes employed in ancient times on horseback. 
Instruments constructed on the same principles were in use amongst 
the Chaldeans and Egyptians at an early period; that of Ctesibius of 
Alexandria being an improvement over those of more ancient times. 
The invention in Western Asia was doubtless independent of that in 
Eastern, both being the result of similar wants. Clepsydras were sub- 
sequently formed of a succession of vessels communicating by tubes 
passing through figures of dragons and other images, which were ren- 
dered still more ornamental by the indices being held in the hands of 
geniul. The earliest application of motion to the clepsydra appears to 
have been in the reign of Shunti A. Dp. 126-145, by Tsiang-hung, who 
constructed a sort of orrery representing the apparent motion of the 
heavenly bodies around the earth, which was kept in motion by 
dropping water. There is also a reference to an instrument of this 
description in the third century. 
In the sixth century an instrument was in use which indicated the 
course of time by the weight of water, as it gradually came from the 
beak of a bird, and was received in a vessel on a balance, every pound 
representing a kih. About this time mercury began to be employed in 
clepsydras instead of water, which rendered the aid of heat in winter 
unnecessary. Changes were made also in the relative number of kih 
for day and night, so as to vary with the seasons as in Europe. Monks 
of the Romish Church devoted considerable attention to the construe- 
tion of instruments for measuring time; in like manner also, Budhist 
monks in their silent retreats, but at an earlier period, similarly oceu- 
pied themselves. Several contrivances to measure time are mentioned 
in Chinese history as the invention of priests. One was a perforated 
copper vessel, placed in a tub of water, which gradually filled and sunk 
every hour; such a rude machine required of course constant attention. 
Although their knowledge of hydro-dynamies is limited, the Chinese 
appear to have been the first to invent the form of clepsydra to which 
the term water clock is alone properly applied—that is to say, an appar- 
atus which rendered watching unnecessary by striking the hours, 
Until the beginning of the eighth century the persons employed to 
watch the clepsydra in palaces and public places struck bells or drums 
at every kih, but at this period a clock was constructed, consisting of 
four vessels, with machinery which caused a drum to be struck by day 
and a bell by night, to indicate the hours and watches. No deserip- 
tion of the works of this interesting invention can be found. It is pos- 
sible however that the Saracens may have anticipated the Chinese in 
the invention of water clocks. In the History of the Tang Dynasty it 
is stated that in the Fublin country (which in this instance doubtless 
means Persia, though the geographer Sii makes it Judea), there is a 
clepsydra on a terrace near the palace formed of a balance which con- 
tained twelve metallic balls, one of which fell every hour on a beil, and 
