

18 



HYDRODYNAMICS. 



of line which ruts Uie semicircle. As C h i tlu 

 longest line which can be drawn within (he semicircle 

 ater spouting thim C will reach the greatest 

 hnriaunlal distance a, and Uiat range, if in vacim. 

 would he equal to twit e the leii-tli of line drawn 

 from the point of discharge to the semicircle. 

 Though water will n-e in pipes us Inu'li as Uie 

 surface of (he head from which it is supplied; yet in 

 perpendicular jets it can never rise so hkh. IH.MU-. 

 of the resistance of the air. and the friction of the 

 mljtimne. The best kind of adjutage is the end of 

 the tube covered with a thin plate, in which is made 

 a smooth hole much less Uian the bore of the tube. 

 In such an adjutage Uie water will ascend ii 

 regular shape, and find little friction 

 through Uie thin plate. 



'1 he second division of the subject, mentioned in 

 the beginning of Uiis article, is of the greatest prac- 

 tical utility, as embracing an account of the various 

 pumps and machines which have been employed to 

 raise water: and numerous as these may appear, it 

 will he found that they may all be comprehended 

 under four general heads : I. those machines in 

 which water is lifted in vessels by the application of 

 some mechanical force to them. The earlier 

 hydraulic machines were constructed on this prin- 

 ciple, which is the simplest ; such are the Persian 

 wheel, consisting of upright buckets attached to the 

 rim of a wheel, moving in a reservoir of water ; the 

 buckets are fillet! at bottom, as they pass through the 

 water, and emptied at top, so that the water is raised a 

 height equal to the diameter of the wheel. The wheel 

 may be turned by living power, or, if in running water, 

 by fastening float hoards to the circumference. A 

 modification, and decided improvement on Uie Persian 

 wheel has been long in use in Scotland. This wheel 

 was the invention of Mr George Micke, an in- 

 genious millwright of Alloa, in Clackmannanshire. 

 (See Pertian Wheel.) The Archimedian screw, the 

 bucket-engine or chain-pump, and the rope-pump of 

 Vera, are modifications 

 of the same principle. 

 The Chain Pump is 

 shown in the annexed 

 figure : it usually consists 

 of a succession of long 

 links of metal rods, re- 

 volving like an endless 

 rope over two wheels e /, 

 one of which, /, must 

 be under water. Oil 

 this chain, between each 

 joint, is fixed a flat piece 

 of wood or metal, d d d, 

 usually square, which is 

 supported and kept in its 

 place by the projecting 

 arms of the wheels / 

 and f. though at the 

 same time Uiey are per- 

 milted to turn with the 



same freedom as the chain ; the wheel e is turned 

 by a winch, which causes the whole chain to move ; 

 one side of it passing upwards, while the oUier side is 

 continually descending in the same direction. The 

 ascending side of the chain is made to pass through a 

 box or pipe, one end of which is immersed in the 

 water, the other end nearly reaching the upper 

 wheel ; this box corresponds in shape with the 

 SIM of the plates which fit pretty closely, and form 

 be pump. The succession of plates passing upward 

 through the trunk, forms a succession of cavities 

 which are filled with water, and are constantly 

 discliarged at Uie top. From the formation of this 

 pump it will only work in deep water, and conse- 



quently cannot drain a reservoir to the bottom ; but 

 it has the advantage of not becoming choked with 

 smd <>r w.-pds ; ami though some of its advantages 

 may be lost by Uie plates not fitting closely to the 

 trunk, and thereby allowing some of the water to 

 drain out, yet as an upper chamber can only leak 

 into one below, if the motion of the machinery be 

 very rapid, it cannot lose any considerable quantity 

 of water. It is for these reasons frequently used in 

 draining the water from Uie foundations of bridges, 

 docks, and other large works. If the top and lx>t- 

 tom wheeU, ef, of this machine be retained, while 

 the tube or trunk is taken away, and a number of 

 small boxes or buckets be attached to the chain instead 

 of the plates d d d, the machine then becomes a 

 bucket engine, which is but another form of the Per- 

 sian wheel already described. A pump on this prin- 

 ciple is used in ships, and is called a chain pump. 



2. The next class of machines are those in which 

 the water is raised by the pressure of the atmosphere, 

 and comprises all those machines to which the name 

 of pump is more particularly applied. These act 

 entirely by removing the pressure of the atmosphere 

 from the surface of the water, which may thus be 

 raised to the height of about thirty-two feet. (See 

 Atmosphere Air.) Whenever it becomes necessary 

 to raise water to greater heights, the third class of 

 machines, or those which act by compression on the 

 water, either immediately or by the intervention of 

 condensed air, are employed. All pumps of this 

 description are called forcing-pumps. (See Pump.) 

 Although atmospheric pressure is not necessary in 

 the construction of forcing-pumps, it is, in most 

 cases, resorted to for raising the water, in the first 

 place, into the body of the pump, where the forcing 

 action takes place. In machines of this kind, the 

 water may be raised to any height. 



The common suction pump consists of a hollow 

 cylinder A, of wood or metal, which contains a pis- 

 ton B, stuffed so as to move up or 

 down in the cylinder easily, and yet 

 be air tight : to this piston there is 

 attached a rod which will reach at 

 least to the top of the cylinder when 

 the piston is at the bottom. In Uie 

 piston there is a valve which opens 

 upwards, and at the bottom of the 

 cylinder there is another valve C 

 also rising upwards, and which 

 covers the orifice of a tube fixed to 

 the bottom of the cylinder, and 

 reaching to the well from whence 

 the water is to be drawn. This tube is commonly 

 called the suction tube, and the cylinder, the body of 

 the pump. When the piston is at the bottom of the 

 cylinder, there can be no air, or at least very little 

 between it and the valve C, for as the piston was 

 pushed down, Uie valve in it would allow the air to 

 fscape instead of being condensed, and when it is 

 drawn up, the pressure of the air would shut the 

 valve, and there would be a vacuum produced in the 

 )ody of the cylinder when the piston arrived at Uie 

 top. But the ah- in the cylinder being very much 

 rarefied, the pressure of the valve C on the water at 

 the bottom will be greatly less than that of the 

 external atmosphere on the surface of the water in 

 .he well ; therefore, the water will be pressed up the 

 jump to a height not exceeding thirty-two feet. As 

 .he valves shut downwards, the water is prevented 

 rom returning, and the same operation being 

 repeated, the water may be raised to any height, 

 not exceeding the above limit in any quantity. 



The quantity of water discharged in a given time, 

 s determined by considering that at each stroke of 

 the piston a quantity is discharged equal to a cylin- 



