FIG. 3.—AN EARLY FORM OF THE WATER-CLOCK.
If we could step on board a Malay proa we should see floating in a bucket of water a cocoanut shell having a small perforation through which the water by slow degrees finds its way into the interior. This orifice is so perforated that the shell will fill and sink in an hour, when the man on watch calls the time and sets it to float again. This sinking cocoanut shell, the first form of the water-clock, is the clock from which has been developed the timepiece of to-day. With it, therefore, the story of the clock really begins. In Northern India the cocoanut shell is replaced by a copper bowl (Fig. 3). At the moment the sinking occurs the attendant announces the hour by striking upon the bowl.
The second step in the development of the water-clock was made in China several thousand years ago. In the earlier Chinese clock the water, instead of finding its way into the vessel from the outside, was placed inside and allowed to trickle out through a hole in the bottom and fall into a vessel below. In the lower vessel was a float which rose with the water. To the float was attached an indicator which pointed out the hours as the water rose. By this arrangement, when the upper vessel was full, the water, by reason of greater pressure, ran out faster at first than at any other time. The indicator, therefore, at first rose faster than it ought, and after a while did not rise as fast as it ought to. After centuries of experience with the two-vessel arrangement, a third vessel was brought upon the scene. This was placed above the upper vessel, which now became the middle vessel. As fast as water flowed from the middle vessel it was replaced by a stream flowing from the one above it. The depth of the water in the middle vessel did not change, and the water flowed into the lowest vessel at a uniform rate. Finally a fourth vessel was brought into use. The Chinese water-clock shown in (Fig. 4) has been running in the city of Canton for nearly six hundred years. Every afternoon at five, since 1321, the lowest jar has been emptied into the uppermost one and the clock thus wound up for another day.
FIG. 5.—AN EARLY GREEK CLEPSYDRA.
To follow the further development of the water-clock we must pass from China to Greece. In their early history the Greeks had nothing better than the sun-dial with which to measure time. About the middle of the fifth century B. C. there arose at Athens a need for a better timepiece. In the public assembly the orators were consuming too much time, and in the courts of law the speeches of the lawyers were too long. It was a common thing for a lawyer to harangue his audience for seven or eight hours. To save the city from being talked to death a time-check of some kind became necessary. The sun-dial would not answer, for the sun did not always shine, even in sunny Greece; so the idea of the water-clock was borrowed. A certain amount of water was placed in an amphora (urn), in the bottom of which was a small hole through which the water might slowly flow (Fig. 5). When the amphora was empty the speaker had to stop talking. The Greeks called the water-clock a clepsydra, which means "the water steals away." The orator whose time was limited by a certain amount of water would keep his eye on the clepsydra, just as a speaker in our time keeps his eye on the clock, and if he were interrupted he would shout to the attendant, "You there, stop the water," or would say to the one who interrupted him, "Remember, sir, you are in my water." The story goes that upon one occasion the speaker stopped every now and then to take a drink; the orator's speech, it seems, was as dry as his throat, and a bystander cried out: "Drink out of the clepsydra, and then you will give pleasure both to yourself and to your audience."
FIG. 6.—AN IMPROVED GREEK CLEPSYDRA.