Author(s): D. R. Blackman

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Abstract: The water clock or clepsydra(which is Greek_forwater-thief)is of considerable antiquity. Theywere common in the classical world,in china,anddoubtless in civi1izations less wel1 documented. clepsydrae were appropriate for measuring shorterintervals,the sun dial in whatever form being usedfor more extended periods. Te basic idea,ofcourse,is to meter water through a small orifice.Surface tension effects make performance unreliablein clocks which drain their reservoir to emptyness,a fact(without explanation)which kept the fillingtype popular to the last.A nunber of clocks havesurvi ved from antiquity,the common form being atruncated cone,apex down,which sank when time wasup although many also carried internal graduations·Such simple timers were used,for example,toregulate the tine allowed to Roman barristers;thesatirist Martial has a few characteristicallybiting 1ines about the advocate whose failing voiceis revived by a draught from the clepsydra.Thereare descriptions of more elaborate versions,principally from that incontinent inventor Hero ofAlexandria,which could be persuaded to cope withthe variable length of the hour by which the daywas marked until well past the tine that thewidespread use of the mechanical clock made itinconvenient(in this system,there were always 12hours between dawn and dusk)。

DOI:

Year: 1985