Once well established and understood in principle, the clepsydra became widely known over the ancient world, and underwent a variety of improvements and modifications in form. These latter chiefly dealt with making it more legible. Means were devised, for instance, to make it ring a bell when the water reached a certain height. And thus the alarm principle was very early brought into use. Later on, after the development of mechanical devices like the pulley and the toothed wheel or gear, the pointer was by these means constructed to move faster or slower than the rate at which the water rose, or to revolve upon a circular dial on which the hours were marked. And thus we owe to the clepsydra the origin of the modern clockface as well as of the alarm. Later still, by a more complex ingenuity, devices were arranged to strike the hours or to move mechanical figures, in fact, to perform all the functions of a clockwork which was both driven and regulated by hydraulic power. The single hour hand, however, remained in place of our two or three hands moving at different speeds, as in the modern clock or watch. The clockwork also remained primitive in construction compared with our own. Clepsydrae were always expensive, because accurate mechanical work was never cheapened until modern time. Rather they were made marvels of patient ingenuity and lavish ornament. Cunning oriental craftsmen spent their skill upon elaborate mechanism and costly decorations. The clepsydra thus became first what other time-pieces later became—a triumph of the jeweler's craft—a gift for kings. And the Greeks, who beautified everything that they touched, made it at once more accurate and more artistic. The clepsydra may thus fairly claim to have been the first _mechanical_ device for measuring time, as contrasted with the sun-dial which was really an astronomical instrument; and thus the direct ancestor of the mechanical clocks of later days. Some authorities, indeed, on the strength of certain very ancient allusions to its use in China and elsewhere, claim for it an antiquity prior to the sun-dial itself. There seems, however, to be no reason for supposing that the discovery of a mechanical law like the regular flow of water antedated so obvious a discovery as the motion of a shadow upon the ground. The explanation is probably that the invention of the clepsydra did precede the scientific perfecting of the sun-dial by the inclinations of the gnomon; which may have taken place about the time of the correction of the Babylonian calendar in 747 B. C. Not long after this date we meet with frequent references to the placing of a clepsydra in the public square of some old city, or to its use in astronomical calculations. To this, of course, its property of running by night was peculiarly adapted.