The Water-clock consisted of a large vessel filled with water, on the
surface of which was placed a smaller vessel, really a gong, with a
hole in the bottom. The water gradually filled the smaller vessel, and
it sank. The Time-boy sat beside the Water-clock and as soon as the
vessel sank he fished it out, emptied it, struck the gong one or more
times and set it on the water again.]
During the night and also in cloudy weather the sun-dial was useless,
and we read that the priests of the temples and monks of more modern
times “went out to observe the stars” to make a guess at the time
of night. The most prominent type after the shadow devices was the
“water-clock” or “clepsydra,” but many other methods were used, such as
candles, oil lamps, and in comparatively late times, the sand-glass.
The fundamental principle of all water-clocks is the escape of water
from a vessel through a small hole. It is evident that such a vessel
would empty itself each time it is filled in very nearly the same
time. The reverse of this has been used, as shown in the picture of
the Time-boy of India. He sat in front of a large vessel of water and
floated a bronze cup having a small hole in its bottom in this large
vessel, and as the water ran in through the hole the cup sank. The boy
then fished it up and struck one or more blows on it as a gong. This he
continued and a rude division of time was obtained--while the boy kept
awake!
[Illustration: Drawing from description by James Arthur.