32; 



LECTURE XXVIII. 



ON HYDRAULIC MACHINES. 



VV E 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 waterwheel, 

 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 M'^hole 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 verti- 

 cal or in an inclined position. Such M'heels are frequently used for draining 

 fens, and are turned by windmills ; the floatboards are not placed in the di- 

 rection which would be best for an undershot wheel, but on the same princi- 

 ple, so as to be perpendicular to the surface when they rise out of it, in order 

 that the water may the more easily flow off them. (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 



