HYDRODYNAMICS. 



565 



Wuer. double of the aperture at b. To a height about 1* feet 

 Ugl"* above CD, the tube should be completely air-tight, as 



i^*~^- well as the vesselCDEF.butabovc that part the tube d B 

 may be perforated in every part with holes. M. Ven- 

 turi has calculated, that the quantity of air which passes 

 in one second into the tnbe is =6.1 a*+/(a + /> 1.4) 

 0.4 a* >/(a X 0. 1 ), where ./ is the diameter of the aperture 

 at 6, and b the diameter of the tube rfB. From this quan- 

 tity about one-fourth should be deducted in practice, 

 on account of the dashing of the scattered water against 

 the lower part of the tubes. If the pipe CIK does not 

 discharge all the air which is generated, the surface of 

 the water hi the vessel will descend, and part of the 

 air will issue out of the lower apertures of the tube d B. 



k'cr.ur..:. Phenomena similar to those produced by the water- 

 "**' blowing machine have been observed in nature. At 

 the foot of the cascades which fall from the glacier of 

 Roche Melon, on the naked rock of La Novalese to- 

 wards Mount Cenis, Venturi found that the force of the 

 wind arising from the air dragged down by the water, 

 could scarcely be withstood. The venlaroli or natural 

 blasts, which are most frequently found to issue from 

 volcanic mountains, arise from the air carried down 

 the hollows by the falls of water ; and what are railed 

 the rain nindi have the same origin. See Kircher's 

 Mundus Subttrraneut, lib. xiv. cap. 5. edit. 1663. Bar- 

 thes, Mem. det Scavamt Elrangert, torn. iii. p. 378. 

 Dietrich, diet de Mineral det Pyrenett, p. 48, 49. 

 Fabri, Pkytic. Trad. lib. ii. prop. 243. Belidor, Arch. 

 Hydrant, torn ii. p. 1. Mariotte, Trait f det Mouv. 

 det Eata, Part i Disc. 3. Arlt et Metiert, Art. des 

 Forges, p. 88. Venturi in \icfioitont Journal, torn. ii. 

 p. 487. McttoitoHi Journal, vol. i. 4to, p. Wt9, and 

 vol. xii. 8vo, p. 48. Wolfius, Opera Mathemalka, torn. i. 

 p. 830. Lewis's Commerce of Arlt. Journal det Mmet, 

 No. 91. 



8. Deter iplion of the Gaining and looting Bucket t. 



This very ingenious machine seems to have been 

 first proposed by Schottus, but was afterwards greatly 

 improved and actually constructed by George Gervet, 

 (| , for Sir John Chester, Bart, at .his seat at Chichley in 

 Buckinghamshire. The object of this machine is to 



Gaining 

 n ^ Losing 



from a well or spring A, Fig. 10. to a re* 

 serroir R. In order to effect this, a wheel WW, 6 feet 

 in diameter, i* fixed above R, and on the same axis 

 another wheel tc ro, 2 feet in diameter. To the circum- 

 ference of W i* fixed a chain \V r, to which is hung a 

 small backet b with a valve in its bottom, and suspend- 

 ed M seen at 6 in fit. A. To the circumference of 

 t M fixed another chain m my, fastened to a rod y z, 

 to which is suspended the large bucket B, with a valve 

 in its bottom, a* seen abovr B. This valve is fixed at 

 the end of the am o B, and is kept in its place by the 

 weight m, acting at the end of the lever M o, whose 

 fulcrum is at n ; but is raised from it* place by raising 

 the arm mo, as shewn in Fig. II. 



Let us now suppose that the small bucket b is filled 

 with water, and that in consequence of water being 

 poured into the Urge bucket B, this bucket descends. 

 The bucket b will therefore ascend till it strikes the 

 hook at i. This hook catching the edge of the bucket, 

 turns it to a side, as shewn in Tig. A. and empties it 

 into the reservoir R. By this time the descending buc- 

 ket B has reached nearly the bottom of the cistern ; /. 

 The arm sso of the lever falling upon the projection M 

 is rmrtl, M shewn in Fig. B, The valve in the bottom 

 is consequently raised also, and the water is discharged 

 at B into the cistern Z. The small bucket b is now an 

 i for B, in consequence of its acting at the 



end of a longer lever, and therefore b descends to the 



cistern A, while B ascends to the position it has in the 



figure. When b reaches the cistern A, the lower end of 



the valve strikes against a fixed obstacle ; it is therefore '~<~~ 



raised out of its place, and admits the water of the cis- 



tern into the bucket. At the same instant the arm 



o n of the lever in the large bucket B striking against 



the bottom of a valve, seen below a, in a branch a of 



the cistern A, raises it, and allows the water from the 



cistern to run into the bucket B, till the weight of the 



bucket is sufficient to raise 6 out of the cistern A. As 



soon as it has received this weight of water it descends, 



the valve below a falls into its place, the valve in the 



bottom of 6 also falls into its place, when it rises above 



the fixed obstacle, and the bucket b ascends as before, 



to discharge its contents into the reservoir, while the 



large bucket descends to M to get rid of its load of 



waste water. It is obvious that the equilibrium of the 



chains and rods will be different in different positions 



of the buckets. When b is at R, and B at Z, B will be 



loaded with an additional quantity of chain. In order 



to regulate the weight of the chains in every position, 



a quadrant Q moves round C as a centre, and a chain 



c (/attached to the point C of the rod c r, is fixed to the 



lower end d of the arch d Q. A weight X is also fixed 



at the end of the radius d C. Now when B is clown at 



7., \ will have descended to p, and from acting at the 



end of a shorter lever, will be a less load upon the rod 



c z than when it had the position at X ; that is, the ad- 



ditional weight which the bucket B hits received from 



the increase of its chain is counterbalanced by the di- 



minution of weight occasioned by the descent of CX into 



the position CP. Desagulier* remarks, that one hogs- 



head falling 10 feet will raise very nearly one hogshead 



10 feet, or one-fourth of a hogshead 40 feet. 



9. Detcriplio* of the Scoop Wheel 



The scoop wheel is intended to raise water through Scoop 

 a height equal to its semidiameter. It is represented by wheel. 

 WW m Fig. 1, and consists of a number of semicircu- J>LAT * 

 lar partitions, shewn in the Figure. These partitions are CCCXX 'V- 

 open at both ends, vis. at the circumference and at the * ]< 

 centre of the machine. As the wheel is turned round 

 in the direction WXW, either by the hand or by any 

 other power, the scoops take up the water, which gra- 

 dually descends during the rotation of the wheel, till it 

 runs into its hollow axle, which again discharges it in- 

 to a spout O. The scoop wheel is one of the forms in 

 which the Persian wheel is generally described. 



10. Description nfthe Periian Wheel. 



The Persian wheel is a double water wheel, with float- Prniaa 

 boards on one side, and a series of buckets on the other, *''! 

 which are moveable about an axis above their centre of 

 gravity. The wheel is placed in a stream, which puts 

 it in motion, by acting upon its floatboards. As the 

 wheel turns, the moveable buckets dip in the water, and 

 ascend filled with fluid. But when they reach the 

 highest point, their lower ends strike against a fixed 

 obstacle, so as to make them empty themselves into 

 a reservoir placed at the top of the wheel. See Fergu- 

 son's Lrcturet, vol. i. p. 180. 



Another form of the Persian wheel is shewn in Fig. Fig. t. 

 2, where WW is a common bucket wheel, moving in 

 the direction WOW. The buckets flipping in the wa- 

 tt r M N. rise filled with it, and discharge their contents 

 into the reservoir O near the summit of the wheel. 

 The wheel for draining the moss of Blairdrummond 

 belongs to this class. It is driven by floatboarda fixed 

 on its periphery like the common undershot wheel, and 



