rn. These early clocks were used when equal measurements of time needed to be established. For example, if two orators were to be allotted the same amount of time to speak before an assembly, a water clock of this nature would have been constructed for the occasion. In the second century BC., a man named Ctesibus created a more elaborate water clock for measuring the time of day. The Clepsydra, as it is called, consisted of four major parts: a vessel for providing a constant supply of water (B), a reservoir and notched floatation rod (F), a display (G), and a device for adjusting the flow of water into the vessel (D). Water was continually poured into the vessel (B), with the overflow escaping from a pipe (I). Water flowed from this vessel into the reservoir at a constant rate. As the reservoir filled with water, the floating, notched rod ascended at a constant rate. This rod was attached to the display (G), which indicated the time of day. The Greeks divided the day into twelve hours of unequal length to insure an equal division of day and night. Because the Greeks divided the day into hours of unequal length, it was necessary to include a device (D) to regulate the flow of water from the vessel (B) into the reservoir (F). By raising the flat, circular cap in the conical vessel (B), the flow of water could be increased, decreasing the length of an hour. In the summer, the day is longer than the night, and in the winter the reciprocal is true. Therefore, in the summer, the clock would be adjusted to extend the length of each day hour. A second way the Greeks standardized the length of a day was by modifying the clock display. A cylinder with sloping hour lines was used instead of a circular face. The mechanism worked as follows: as water collected in the reservoir, a pointer would raise as the cylindrical display rotated. In this manner, the pointer would gradually trace the course of the adjusted hours on the cylindrical display. Howev...
