1 7 S Kofices re/peSling Neu/ Booh. 



and which floats fome time on the water, but which aftet il 

 certain period, difcovered by repeated trial, becomes immcr- 

 fed. It was afterwards contrived to keep the water-clock al- 

 ways full, by fuffering the fame quantity of water to run in 

 as that which flowed out, that equal portions of time might 

 be indicated bv an equal fall. A funnel of inverted pyramid 

 was then employed, in which the water defcendcd in unequal 

 parts, but through equal degrees marked out on a fcale. In 

 the courfe of time the knowledge of aftronomy was applied 

 to theie clocks, and fome were conftrufted in a vcrv ingeni- 

 ous manner : of this kind was the annphoriaim, which the 

 author defcribes; alfo the retrograding clock, and winter water- 

 clock. Plato brought the lirll water-clock to Greece. The 

 firft that ever appeared at Rome was fliown by Scipio Nafica, 

 about the year 157 before Clirift : but foon after thefe clocks 

 were common, not only at Rome, but in other towns of the 

 Roman empire. When Julius Caefar invaded Britain, he 

 found that the inhabitants had water-clocks. In general they 

 were more prized than fun-dials. Athenaeus conftruftcd a 

 clock which indicated the hours by the hiffing noifeof the 

 air forced through a narrow hole by the preifure of water. 

 Together with public fun-dials, public water-clocks were alfo 

 foon introduced. Thefe were eiiablilhed even in the palaces of 

 the great. That the hours as announced by thefe water-clocks 

 may be more eafily made known to the public, the Turks 

 have criers pofted on high towers, — and the Chinefc, perfons 

 who flrike on large bells. The .Tapanefe employ burning 

 matches to indicate the time, and announce the hours in the 

 fame manner as the Chinefe. The ufe which Hipparchus 

 and Ptolemy made of water-clocks contributed to their im- 

 provement : they were much improved by Hero, but during 

 the next feven centuries nothing was done in this refpeft. 

 The clocks of Boethius, that which Harun al Rafchid fent as 

 a prefent to Charlemagne, and that of the philofopher Leo 

 of Conliantinople, were much celebrated, though the in- 

 vention of clocks with wheel-work rendered water-clocks un- 

 neceflary. The latter, however, continued fome time after 

 in ufe; and about the year 1660 water-clocks in the form of 

 a drum, which are thofe called properly at prefent water^ 

 clocks, were invented it is probable in Italy, but rather for 

 curiofity tlian for real ufe. The obfervation that the water 

 foon evaporated, may have given occafion to fand being ufcd 

 in fuch clocks inftead of water. The period when this change 

 was made is not known. There is reafon onlv to conjedure 

 that the Kjivptiansand Chaldeans had hour glalVes. In the 

 Monachal Laws the word klcpfammidia occurs only in writ- 

 ings of the eighth century ; and it was not till a much later 

 4 , period 



