HYD 



HYD 



excavation in the pipe, as shown by the 

 dotted lines, and by driving nails through, 

 to obstruct the ball from rising too high. 



These are the general principles of the 

 valves in common use ; though we could 

 enumerate a great variety, which have all 

 been strongly recommended, but in prac- 

 tice proved very deficient. We shall, 

 therefore, proceed with the detail of hy- 

 draulic machines, commencing with those 

 which supply the place of pumps, by rais- 

 ing water to given heights. The most 

 simple, and, perhaps, the most ancient, 

 is the spiral pump of Archimedes. It con- 

 sists of a cylinder of wood, about a foot in 

 diameter, and of any length at pleasure : 

 on this a leaden pipe of any bore is wound 

 from the bottom to the top, spirally. 

 When the bottom of the cylinder revolves 

 in the water, (by means of a common 

 Winch handle at the top, and of a pintle 

 in the centre of its base, which rests in a 

 box or step for that purpose below) the 

 reclined position, as shown in fig. 16, oc- 

 casions the water to enter the bottom of 

 the pipe, and to be carried by the revolu- 

 tions of the cylinder completely up to the 

 top, where it discharges into a vessel. 

 This, however, raises but a small quanti- 

 ty, though the height may be indefinite : 

 therefore, where such a machine is in 

 use, it will be found eligible to have the 

 whole cylinder covered with various 

 pipes, like the bands in a rope, whereby 

 the quantity of water raised would be pro- 

 portionably increased with very little ad- 

 dition of power : the greatest resistance 

 would arise from the friction upon the 

 supporting axis, especially the lower one 

 under the surface. Some of these ma- 

 chines have been worked in strong run- 

 nig brooks, by means of water-boards, 

 the same as the great wheels in under- 

 shot mills. 



The hom-drum, so called from a number 

 of segments passing from the circumfer- 

 ence of a large flat cylinder to its centre, 

 is an easy mode of raising water. The 

 scoops or mouths, by turns, Hip into the 

 water, and as they rise cause it to pass up 

 the horn or segment, until it is discharg- 

 ed into a trough placed under the end of 

 the axis, which is hollow, and has its pin- 

 tle fastened to a cross, as seen in fig. 17. 

 Such wheels usually work with water (or 

 float) boards ; and some of them have 

 projecting fins, from which rectangular 

 buckets are suspended; these dip into 

 the water as the wheel turns, and succes- 

 sively discharge into a trough, by means 

 of a pin at A, which causes every bucket, 

 as it passes, to turn to a horizontal instead 



of an erect position. The latter invention 

 is ascribed to the Persians. The reader 

 will, no doubt, readily perceive, that a 

 strong current, or other force, is needful 

 to move machines so laden as the Persian 

 wheel, it sometimes raising near a ton of 

 water in each revolution ; and that no- 

 thing but the necessity for raising water 

 could induce to so great a loss of power. 

 When treating of MILLS, and of PUMPS, as 

 also of PNEUMATICS, with which HYDRAU. 

 LICS are often intimately blended, we 

 shall enlarge more on this subject ; for 

 the present, concluding with the ordinary 

 mode of apply ing a water wheel to pumps, 

 as may be seen at London Bridge, and in 

 a great variety of instances, where im- 

 mense quantities are raised by means of 

 running water, referring to the article 

 STEAM-ENGINE for the operations depen- 

 dant on that power. We have, in speak- 

 ing of FLUIDS, said much on their proper- 

 ties, which the reader will find both amus- 

 ing and instructive : indeed, we consider 

 this doctrine to be indispensable, as a 

 study, with those who court an intimate 

 acquaintance with hydraulics. 



Fig. 18, shows the section of three forc- 

 ing pumps, o p q t with their, pistons, as 

 acted upon by three cranks, a b c, each 

 equally radiated from the branch d e, and 

 moved by a wajter wheel, of which/ is the 

 axis : it is plain that the several cranks 

 stand at an angle of 120 degrees respec- 

 tively. By this means there is a counter- 

 balance among them mutually, and each 

 gives one stroke or plunge during each 

 revolution of the wheel. If the wheel is 

 large, it will of course move slowly ; and, 

 unless the pumps be very large, but little 

 water will be raised : therefore^ is usual 

 to acelerate the motion of the branch 

 bearing the cranks, by means of a spur, 

 or of a trundle, turned by the water-wheel, 

 and bearmg such proportion thereto as 

 the required increase of velocity may de- 

 mand. For the manner of applying such 

 a spur, &c. see the article MILL-WORK. 



HYDRAULIC ON, -water-organ, in mu- 

 sic, an instrument acted upon by water, 

 the invention of which is said to be of 

 higher antiquity than that of the wind 

 organ. 



HYDROCELE, in surgery, denotes any 

 hernia arising from water, but is particu- 

 larly used for such a one of the scrotum, 

 which sometimes grows to the size of one's 

 head, without pain, but extremely troubler 

 some to the patient. See SURGERY, 



HYDROCEPHALUS, ui surgery, a pre- 

 ternatural distention of the head to an un- 

 common siie, by a stagnation and ex- 



