ON THE REGULATION OF HYDRAULIC FORCES. 241 



xxxiii. 3. Nicholson's Journal, i. 37 (Baume's), 110. Nicholson's Hyd. Manch. 

 Mem. ii. 370. Nat. Ph. ii. 16. Quin's, Tr. Soc. Arts, yiii. 198. Schmidt's, 

 Gren's Journal der Physik, vii. 186. Charles's Biot's Traite de Physique, i. 114; 

 Benoit Theorie Generale des Pese -liqueurs, 1821. 



Hydraulic Architecture. Belidor Sommaired'un Cours d' Architecture Hydrau- 

 lique, Paris, 1720. Architecture Hydraulique, 4 vols. 4to, 1737-53. Erskine, A 

 Dissertation on Rivers, &c. Loud, 1770. Prony, Nouvelle Architecture Hydraulique, 

 2 vols. 4to, Paris, 1790-6. Gilly, Grundriss zu den Vorlesungen iiber Wasserbau- 

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 Reports. Coulomb sur les Moyens d'Executer sous 1'Eautoutes sortes de Travaux 

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 sur la Fondation des Ouvrages Hyd. 4to, 1829. 



LECTURE XXVII. 



ON THE REGULATION OF HYDRAULIC FORCES. 



THOSE modifications of the motions of fluids which are employed either 

 for conducting them from place to place, or for applying their powers to 

 the production of mechanical effects, may be considered as constituting a 

 separate division of practical hydraulics, which is analogous to the subject 

 of general machinery in practical mechanics. 



A supply of water may be obtained from a reservoir situated above the 

 level at which it is wanted, whatever its distance may be, either by means 

 of open canals, or aqueducts, or of closed pipes. Where an uninterrupted 

 declivity cannot be obtained, it is necessary to employ pipes, which may be 

 bent upwards or downwards at pleasure, provided that no part of them be 

 more than thirty feet above the reservoir, and when the pipe is once filled, 

 the water will continue to flow from the lower orifice ; but it is best in all 

 such cases to avoid unnecessary angles ; for when the pipe rises and falls 

 again, a portion of the air, which is always contained in water, is frequently 

 collected in the angle, and very materially impedes the progress of the 

 water through the pipe. When the bent part is wholly below the orifices 

 of the pipe, this air may be discharged by various methods. The ancients 

 used small upright pipes called columnaria, rising from the convexity of 

 the principal pipe, to the level of the reservoir, and suffering the air to 

 escape without wasting any of the water. It may however frequently be 

 inconvenient or impossible to apply a pipe of this kind ; and the same pur- 

 pose may be answered, by fixing on the pipe a box containing a small valve, 

 which opens downwards, and is supported by a float, so as to remain shut 

 while the box is full of water, and to fall open when any air is collected in 

 it. (Plate XXI. Fig. 284.) 



J[f the pipe were formed into a siphon, having its flexure above both 

 orifices, it would be necessary to bend it upwards at the extremities, in order 

 to keep it always full ; but in this case the accumulation of the air would 



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