Chap. 8.] Ancient Hmr-Glasses—Chinese Sand and Water-Clocks. 545

clepsydrse which modern nations continue to use. Nieuhoff observes ofChinese water-clocks, “ they bear a resemblance to some great hour-glasses in shapeand he säys, in several sand was used instead of water.On an ancient bas-relief at Rome , representing the marriage of Thetis andPeleus , Morpheus holds an hour-glass ; and from Athenseus we learn thatthe ancients carried portable ones about with them somewhat as we dowatches.

In another variety of clepsydrse, the sides of the vessel from which thefluid escaped were graduated, somewhat like chemists’ measuring glasses,and the hours announced as the descending surface of the fluid reachedthe marks. If the vessel was of a cylindrical or cubical figure the distancebetween the marks was not uniform, because the water escaped fastest atfirst, in consequence of the greater pressure of the column over the orifice,which pressure constantly diminished with the efflux ; the surface of thefluid could not therefore descend through equal spaces in equal times.When such formed vessels were used, the relative distances of the markswere probably determined by experiment, although they might have beenby calculation. Sometimes the vessels were funnel-shaped, the angle oftheir sides being so adjusted that an equal distance could be preservedbetween the marks—unequal quantities of the fluid escaping in equaltimes. These Instruments were generally made of glass, and a cork orsome floating image, to which a needle was secured, pointed out the houras the water sunk. Pancirollus sayk, the small holes were edefed withgold.

In some clepsydrse the fluid was received into a separate vessel to raisea floating image that pointed as an index to the hours. Sometimes a boywith a rod, Time with his scythe, and Death witb a dart. In this varietyof the Instrument, it was desirable that the quantity of fluid discharged intothe vessel should be uniform at all times ; and to effect this, the floatingsiphon, No. 239, was sometimes used. Such we presume was the clepsydraof Orontes , which was made “ in the form of a small ship floating on thewater, and which emptied itself by means of a siphon placed in the middleof it.” Dr. Harris, not aware of the property of a floating siphon, couldnot perceive how the hours were made equal by this contrivance, which,he’ observes, Orontes devised to remedy the unequal flow of water froman open vessel.—(Lex. Tech.)

Nieuhoff noticing the numerous towns in China , upon the greater partof which, he observes, were clepsydrse, says, “ upon the clock-house tur-rets Stands an instrument which shows the hour of the day by means ofWater, which running from one vessel into another raises a hoard, uponwhich is portrayed a mark for the lime of day ; and you are to observe,there is always a person to notice the time, who every hour signifies thesame to the people by beating upon a drum, and hanging out a board withthe hour writ upon it in large letters.” (Ogilby, Trans. 196.) Montanussays tkese letters were “ a foot and a half long.” See also Purchas’Pil-grimage, 499.

In another dass of ancient clepsydrse, the water dropped upon an over-shot wheel, which turned an index in the centre of a circle, round whichthe hours were marked ; hence our clock and watcb dials. “ The Chinese have other instruments to know the hour of the day, being somewhat likeour clocks with wheels, and they are made to turn with sand as mill-wheels are with water.” (Nieuhoff.) At last solid weights were intro-duced in place of water, and by means of cords gave motion to the index,and thus opened the way still more for the introduetion of modern clocks.

It would appear from the description of clepsydra; by Vitruvius and

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