A Clepsydra

Among the valuable presents sent to the Emperor Charlemagne by Haroun al Raschid, which astonished the Western world by their rarity, and the ingenuity displayed in their construction, was a clepsydra, or water-clock of metal. From the admiration this clock elicited, we are led to presume that the clepsydra-first used by the Romans--was a lost art to the Western people.

The Romans had used the clepsydra to limit time in courts. That of Ctesilaus of Alexandria, 135 B.C., had a little figure which rose with the water, and pointed out the hours. But the more simple ones consisted of a vase filled with water, with a small opening at the bottom, through which the water escaped, drop by drop, into a vessel beneath, which was said by the Romans to steal the water, clepsydra meaning water-stealer. The sides of the vase were divided by lines, and the height of the water marked the time.

But the clepsydra sent to Charlemagne, in its delicate and complicated machinery, showed what great progress mechanical art had made in the East. "It had twelve gates corresponding to the twelve hours. When the hour was striking on the clock, one of the gates opened itself, from which proceeded a regular number of small brass balls; and these, falling in turn on a brazen vessel, marked the hour by the noise which they caused: the eye perceived the hour by the number of opened gates, and the ear by the number of falling balls. At the twelfth hour, twelve small horsemen issued out, each through its gate, and closed them all by their momentum in their course round the dial.

The clepsydra, or water-clock, is still used in some countries; but, the flow of water being affected by temperature and barometric pressure, the pendulum has superseded it in modern times.

The invention of pendulum-clocks is, by some, ascribed to Pacificus, Arch-deacon of Verona, in the ninth century; and by others to Boethius, in the early part of the sixth. The Saracens are said to have had clocks moved by weights in the eleventh century; and, as Dante applies the term to a machine which struck the hours, clocks must have been known in Italy at the end of the thirteenth, or beginning of the fourteenth, century. The most ancient clock of which there is any certain record was erected in a tower of the palace of Charles V., King of France, in 1364, by Henry de Wyck, a German artist. A clock was erected at Strasbourg, in 1370, at Courtray, about the same time, and at Speyer in 1395.

The invention of the pendulum was suggested to Galileo by a circumstance somewhat similar to that which started Newton's mind to the discovery of the theory of gravitation.

When Galileo was standing one day in the Metropolitan Church of Pisa, he observed a lamp, which was suspended from the ceiling, and which had been moved by accident, swing backwards and forwards. Thousands of people might have observed it before; but Galileo, noticing the regularity with which it moved, reflected upon it until he was enabled to perfect the method of measuring time now in used by means of a wheel and pendulum. Watches are said to have been made at Nuremberg as early as 1477, but the watches of that early date bear a very small resemblance to those now in use. Some were immensely large, and some so small that they could be fitted into the top of a walking-stick. As time-keepers, they could have been of very little value until the application of the spiral spring, invented by Hooke, in 1658.