It used to be that time was made for slaves, but now time has made slaves of us. Shift the hands of the clock and the whole nation is forced to change its habits. Time-measuring mechanism is given early prominence in this book because clocks were among the earliest machines invented, and they furnish an example of the wonderful ingenuity of inventors before the dawn of the modern era of machinery. Naturally this chapter must be largely historical. The first thought of measuring time came from the ancient astronomers and astrologers, who, in watching the motions of heavenly bodies, the sun by day and the moon by day and night, found it necessary to keep a record of these motions and sought about for some mechanical means of doing so. The studies of the old astrologers were closely associated with religion, and as a consequence the most advanced intellects were centered upon astronomical matters and incidentally upon horology. Fortunately the design and construction of mechanisms for measuring time were not considered beneath the dignity of the scientists of those early days. Mathematicians felt free to record their investigations in this branch of mechanics, and as a consequence of the early cooperation of science and mechanics in this field much real progress was made, and the development of timepieces was more rapid than that of any other machine. TELLING TIME WITH A LEAKY BUCKET The ancient Egyptians early felt the need of a better clock than the sundial, because it operated only on cloudless days and was absolutely worthless to tell off the hours of darkness. Realizing that time is a measure of motion, they sought for some slowly moving body whose motion could be used to measure time, and naturally they turned to water. The earliest form of clock consisted merely of a leaking bucket. Either the bucket was filled with water which was allowed to escape through a very tiny orifice, or else the heavily loaded bucket was placed in water and the water was allowed to leak into the bucket until it sank. The period it took for a bucket to run dry or for a bucket to fill and sink indicated a lapse of an hour or some other standard of time. The idea of subdividing this period was a later development. As the water leaked out of a bucket, the water level descended, but unfortunately not at a uniform rate. The weight of water in a full bucket made the drops come faster than when the bucket was nearly empty. Consequently the time graduations on the side of the bucket had to be set farther apart at the top of the bucket than at the bottom. Various ingenious schemes were devised for maintaining a uniform discharge. In one type of water clock or clepsydra a conical bucket was used so that there would be a constant relation between the head of water and the volume in the bucket and the time graduations could be spaced uniformly. THE REMARKABLE WATER CLOCK OF CTESIBIUS