250 LECTURE XXVIII. 



hamel, Architecture Navale, 4to, Paris, 1758. Gordon's Principles of Naval Archi- 

 tecture, Lond. 1784. Chapman, Traite de la Construction des Vaisseaux, trans- 

 lated by Inman. Also, Essays, in Papers on Naval Architecture. Atwood on the 

 Stability of Ships, Ph. Tr. 1796, p. 46; 1798, p. 201. Euler on the Construc- 

 tion of Vessels, by Sir G. Shee. Trans. Roy. Ir. Acad. vi. 15. Watson's Elements 

 of Naval Architecture, fol. 1805. 



LECTURE XXVIII. 



ON HYDRAULIC MACHINES. 



WE shall apply the denomination of hydraulic machines to such only, 

 as are intended for counteracting the gravity of water, that is, for raising it 

 from a lower situation to a higher.. The simplest of these are buckets, 

 bucket wheels, and friction ropes ; moveable pipes are the next in order ; 

 and pumps of various kinds constitute the most extensive and the most 

 important part of the subject. Besides these and some other similar 

 machines, hydraulic air vessels and artificial fountains will also require to 

 be examined. 



A series of earthen pitchers, connected by ropes, and turned by trundles 

 or pinions, over which they pass, has long been used in Spain under the 

 name of noria : in this country buckets of wood are sometimes employed 

 in a similar manner. A bucket wheel is the reverse of an overshot water- 

 wheel, and the water may be raised by buckets nearly similar to those 

 which are calculated for receiving it in its descent : sometimes the buckets 

 are hung on pins, so as to remain full during the whole ascent ; but these 

 wheels are liable to be frequently out of repair. Sometimes the reverse of 

 an undershot wheel or rather of a breast wheel, is employed as a throwing 

 wheel, either in a vertical or in an inclined position. Such wheels are 

 frequently used for draining fens, and are turned by windmills ; the float- 

 boards are not placed in the direction which would be best for an undershot 

 wheel, but on the same principle, so as to be perpendicular to the surface 

 when they rise out of it, in order that the water may the more easily flow 

 offthem.* (Plate XXII. Fig. 296.. .298.) 



Instead of a series of buckets connected by ropes or chains, a similar effect 

 is sometimes produced by a simple rope, or a bundle of ropes, passing over 

 a wheel above, and a pulley below, moving with a velocity of about 8 or 10 

 feet in a second, and drawing a certain quantity of water up by its fric- 

 tion. It is probable that the water commonly ascends with about half the 

 velocity of the rope, and on this supposition we might calculate its depth on 

 the rope by comparing its relative motion with that of a little river : but 

 the rules which serve for calculating the velocity of rivers, do not perfectly 

 agree in this case with the results of direct experiments ; for the friction 



* Vitruvius, Architecture, 1. 10, c. 9, translated by Newton, 2 vols. fol. London. 



