444 



SCIENCE 



[N. S. Vol. XXV. No. 638 



But now these cursed dials show their faces, 



All over Rome in streets and public places; 

 And men, to know the hour, the cold stone ques- 

 tion. 



That has no heart, no stomach, no digestion. 

 They watch the creeping shadows — daily thinner — 



Shadows themselves, impatient for their dinner. 

 Give me the good old time-piece, if you please, 



Confoimd the villain that invented these! 



As in Greece so in Rome, the clepsydra 

 followed in the wake of the sundial, and 

 as in the ease of the sundial, Grecian sci- 

 ence and genius had by this time produced 

 a much more perfect instrument than that 

 first used by the Greeks. 



In describing the sundial of Berosus, I 

 stated that by it the day was divided from 

 sunrise to sunset into twelve parts, varying 

 in lengths from day to day, called tem- 

 porary hours. If now the clepsydra and 

 the sundial were to read alike, it was neces- 

 sary that the hours recorded by the clep- 

 sydra should also change from day to day. 

 Various devices were adopted to accomplish 

 this. Further, as the clepsydra could be 

 used throughout the entire day and night, 

 it was necessary to have it record hours of 

 a different length at night from what it 

 did in the day, as each night, i. e., from 

 sunset to sunrise, was divided into twelve 

 hours as well as each day. 



Fig. 1 represents an early form of the 

 clepsydra. It consists of an inverted cone 

 A, with a small aperture at its vertex. The 

 water is supplied through the pipe H and 

 is prevented from rising above a fixed level 

 in A by the waste pipe I, which carries 

 off the superfluous water. Thus there will 

 be a uniform flow of water from the vertex 

 of the cone into the cylindrical vessel and 

 the cork F will rise uniformly, communi- 

 cating its motion through the rod E to the 

 hand G, which indicates the hours on the 

 dial. In order to produce a change in the 

 rate of flow of the water from the conical 

 vessel, as is necessary in having the hand 

 indicate hours of different length from day 

 to day, a solid cone B, similar to A, was 

 plunged into the hollow one, and its posi- 

 tion for any given day or night was indi- 

 cated by the coincidence of a particular one 

 of the adjusting marks on the stem D with 

 the top cross-piece of the frame C. 



A later form of clepsydra, attributed to 

 Ctesibius, who lived during the latter part 

 of the third century b.c.^ is shown in Fig. 2. 

 A is the end of a tube over which an image 

 stands, which is connected with a full reser- 

 voir, and from the eyes of which, consid- 

 ered as invariable apertures, the water con- 

 tinually flows or drops in a regulated man- 

 ner into it ; this tube conveys the water into 



Fig. 1. Early Form of Clepsydra. 



Fig. 2. Clepsydra of Ctesibius. 



