Science . rm flow of water from the vertexof the cone into the cylindrical vessel andthe cork F will rise uniformly, communi-cating its motion through the rod E to thehand G, which indicates the hours on thedial. In order to produce a change in therate of flow of the water from the conicalvessel, as is necessary in having the handindicate hours of different length from dayto day, a solid cone B, similar to A, wasplunged into the hollow one, and its posi-tion for any given day or night was indi-cated by the coincidence of a particular oneof the adjusting marks on the stem D withthe top cross-pi
Science . rm flow of water from the vertexof the cone into the cylindrical vessel andthe cork F will rise uniformly, communi-cating its motion through the rod E to thehand G, which indicates the hours on thedial. In order to produce a change in therate of flow of the water from the conicalvessel, as is necessary in having the handindicate hours of different length from dayto day, a solid cone B, similar to A, wasplunged into the hollow one, and its posi-tion for any given day or night was indi-cated by the coincidence of a particular oneof the adjusting marks on the stem D withthe top cross-piece of the frame C. A later form of clepsydra, attributed toCtesibius, who lived during the latter partof the third century ^ is shown in Fig. is the end of a tube over which an imagestands, 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. Mabch 22, 1907] SCIENCE 445 the top of the cylindrical vessel BCDF,which gradually fiUs, the cork D, with itsattached pillar C, rising at the same the top of this pillar is an image hold-ing an index which points to the divisionson the large column above. Now when thewater rises in the cylindrical vessel it alsorises in the small tube FB, which consti-tutes one leg of a syphon; consequently,when the small tube fills and the index hasmounted to the top of the large column, thewater flows over the bent part B of thesyphon and the vessel is emptied into oneof the six troughs of the waterwheel K,which is thus turned one sixth of a revolu-tion, and the column, by means of the gear-ing shown in the figure, 1/365 of a revolu-tion, during which time the image fallswith its index to the bottom of the column,to be ready for the next day. There areruled around the large column twenty-fivelines properly sloped with
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