236 PHILOSOPHICAL TRANSACTIONS. [aNNO 1746. 



If there be no weight placed at bottom, as x in fig. 5, the piece of brass ] , 

 1 must be so heavy as to keep the cord sbr at a convenient tightness, and also 

 to counterbalance the end of the index ce, provided it be heavier than the 

 other. 



^ Description of a Clepsydra or Water Clock. By the Hon. Charles Hamilton, 



Esq. N°479, p. 171. 



* Fig. 7, pi- 5, represents this machine in perspective. Here an open canal, ee, 

 is .supplied with a constant and equal stream, by the siphon d; and has at each end 

 f f, open pipes, of exactly equal bores, which deliver the water that runs along 

 the canal e, alternately into the vessels gl, g2, in such a quantity, as to raise 

 the water from the mouth of the Tantalus s, to the top of the Tantalus t, ex- 

 actly in an hour. The canal ee is equally poised by the 2 pipes fl, fo, on a 

 centre r; the ends of the canal e, are raised alternately, as the cups zz are de- 

 pressed, to which they are connected by lines running over the pulleys 11. The 

 cups zz, are fixed at each end of the balance mm, which moves up and down on 

 its centre v. 



nl, n2, The edges of 2 wheels or pulleys, moving different ways alternately, 

 and so fitted to the cylinder o, (by oblique teeth both in the cavity of the 

 wheel, and on the cylinder; which, when the wheel n moves one way [i. e. in 

 the direction of the minute hand] meet the teeth of the cylinder, and carry the 

 cylinder with it; and, when n moves the contrary way, slip over those of the 

 cylinder, the teeth no more meeting, but receding from each other ; or it may 

 be done by catches or locks, which require a longer description) one or other of 

 these wheels nn, continually moves o in , the same direction, with an equal and 

 uninterrupted motion ; for the contrivance is such, that the instant one ceases to 

 act, the other begins, and so on. 



A fine chain goes twice round each wheel, having at one end a weight, x, 

 always out of water, which equiponderates with y at the other end, when kept 

 floating at the surface of the water in the vessel g, which y must always be. 

 The two cups zz, one at each end of the balance mm, keep it in equilibrio, till 

 one of them is forced down by the weight and impulse of the water, which it 

 receives from the tantalus s t i ; each of these cups zz, has likewise a tantalus 

 of its own hh, which empties it after the water has done running from g, and 

 leaves the two cups again in equilibrio; q is a drain to carry off the water. '* ' 



Fig. 8 shows the front of the clepsydra, with the dial-plate, the hour and mi- 

 nute hands, and the weight and float belonging to n2. The front of the tantalus 



* N. B. The letters of reference answer to all the 3 figures; some being seen in one, that do not 

 come in sight in the others.— Orig. ..,(i^,v — 



