TIME-KEEPING IN GREECE AND ROME. 385 



the simplest Greek and Komau clepsydra aud differs iu no mechanical 

 respect from the ordinary sand-glass. 



Bat in the days when the Chinese were a progressive people and de- 

 veloped inventions for which Earoi)e had many centuries to wait, this 

 water-clock advanced far beyond the crude thing we have been con- 

 sidering. It would seem that the problem was to increase its usefulness 

 by sub-dividing the unreasonably long intervals required for the com- 

 l>lete emptying of the vessel. If this was done by marking graduations 

 on the inside of the vessel and so noting the decline of the level the 

 difference in its rate could not fail quickly to make itself manifest.. The 

 solution of this problem, not obvious at first, was found in so arranging 

 the vessel that it should discharge into another, where the indication 

 would be read in the rise of the surface, aud contriving to hold the 

 water in the upper vessel at a constant level. This was done by employ- 

 ing a third source, from which there was a constant tlow into the first 

 equal to its discharge. As the head in the middle vessel is thus main- 

 tained constant, the rise in the lowest is made uniform. Another radical 

 improvement enhancing the practical utility of the device was the ar- 

 rangement of ar float on the surface of the water in the lowest vessel. 

 Upon this was an indicator or hand, which iu its rise travelled over an 

 adjacent scale, and so gave a time indication visible at a distance. 



To show what progress this structure implies in the development of 

 the mechanical clock it is worth while to glance a moment at the essen- 

 tial elements of such an instrument. Keduced to its lowest terms a 

 clock consists of three elements only. These are a motor, or source of 

 power, represented in our clocks by a spring or weight; an escape- 

 ment, or a means by which the stored power in the motor is lot off at a 

 measured rate; and a dial, which is but the means by which the rate 

 at which the power is let off is made visible to the eye. In this 

 Chinese water-clock we discover all these elements. Water, acted on 

 by gravity, is a familiar form of motor ; the small perforation through 

 which it slowly trickles drop by drop is a true escapement, doing in 

 its place just what our complicated mechanisms are doing in theirs; 

 and, rude as it may appear, it is one which mechanicians of our 

 time are not ready to dispense with. The visual indication is given 

 by the rise of the float, causing the pointer to pass over the scale. 

 Going backward from this Chinese clock we perceive, but less dis- 

 tinctly, the same elements in the Indian aud Malay devices, in which 

 the operation is reversed. In these the weight of the vessel, held 

 up by the resistance of the water iu which it floats, is the power; 

 the perforation admitting the water by slow degrees is the esca[)e- 

 ment, and the only indicator is the visible sinking of the vessel 

 itself. 



The three devices described correspond in the degree of their per- 

 fection with the conditions of art and culture among the peoples to 

 which they belong; and, as these conditions appear to have been 

 U, Mis, 234—25' 



