562 



HYDRODYNAMICS. 



Archime- 



les's Screw. 



Archime- 

 ries's screw. 

 PLATE 



2. Description of Archimedei's Screw. 

 The screw engine for raising water invented by Ar- 

 chimedes, was formerly constructed so as to consist of 

 a cylinder with a flexible pipe, wrapped round its cir- 

 i ('{XXII cunn<erence Hk* screw ; but it is now more frequently 

 Kie I. ' constructed in the manner shewn in Plate CCCXXII. 

 Fig. 1. where AB is a cylindrical axis, having a flat 

 plate of wood or thin iron, coiled as it were round it 

 like the threads of a screw. The plane of this plate is 

 perpendicular to the surface of the cylindrical axis AB, 

 but inclined to this axis at an angle, which must always 

 exceed the inclination of the cylindrical axis AB to the 

 horizon. This last angle is commonly between 45 and 

 60. This wooden screw, with a very deep thread, is fix- 

 ed in a cylindrical box CDEF, so that we have a spiral 

 hollow groove as it were running up the tube from B to 

 A, which will have the same effect as if a pipe of lead 

 or leather had been coiled round the cylindrical axis. 



The lower end B of the screw is plunged in the wa- 

 ter of the vessel E, which is to be raised to the upper 

 vessel F, and when the screw is turned round its axis, 

 either by a handle or winch placed at A, or by any other 

 power acting upon the pinion at A, the water at E 

 will fall into the hollow spiral groove, and as the screw 

 turns round, the water will necessarily remain in the 

 lower part of the spiral, and will at last reach the top 

 of the spiral pipe, where it is discharged as seen at F. 

 In this engine, therefore, the water rises by a constant 

 descent in the spiral tube. The operation of this en- 

 gine, which appears at first sight to be paradoxical, will 

 be best understood by wrapping a cord spirally round 

 a bottle containing a little water, and inclining the bot- 

 tle at a less angle to the horizon than the inclination of 

 the cord to the axis. It will then be seen, that if wa- 

 ter falls into the lowest part of the spiral when it is at 

 rest, the motion of the bottle about its axis will remove 

 as it were the spiral out from below the water, which 

 must therefore occupy the part of the spiral immediate- 

 ly above it, and so on till the watsr reaches the top of 

 it. When the outer case CDEF is fixed, and the screw 

 revolves within it, the engine is called a water screw, 

 which should be inclined only about 30 to the horizon. 

 As we conceive this engine to be entitled to more 

 notice than it has generally received from practical me- 

 chanics, we have given a drawing of a very excellent 

 screw engine, which was erected in 1816 at the Hurlet 

 Alum works, upon the Water of Levern, near Paisley ; 

 for which we have been indebted to the kindness 

 of John Wilson, Esq. one of the proprietors. The wa- 

 ter-wheel A, constructed of iron, with wooden buckets, 

 (see Plate CCCXXII. Fig. 2.) is 12 feet diameter, and 

 conveys its motion to the screw by the bevel wheels C, 

 C, and the shafts B, B, 126 feet long, and 5 inches 

 diameter. At the end of the shaft B is fixed another 

 bevel wheel D, which works in a similar wheel D', fixed 

 on the circumference of the screw which rests upon an 

 inclined plane of solid masonry, and is inclined 37 30' 

 to the horizon. The axis KK of the screw, which is 

 represented without its covering in Fig. 2. No. 2. is oc- 

 tagonal, and 8 inches in diameter. The diameter of the 

 spiral is 22 inches, and the thickness of the covering 

 2 inches, so that the whole diameter is 26 inches. 

 The distance of the threads is 9 inches, and their num. 

 ber 168. The thickness of the spiral is 2 inches, so 

 that the spiral tube in which the fluid is to be raised is 

 7 inches wide, and 7 inches deep. The screw is sup- 

 ported on five sets of friction rollers, constructed as 

 shewn at L in No. 3; two rollers having been found 



3 



Witer 

 sc.-ew. 



preferable to a greater number, which were at first em- Arclnme- 

 ployed. The well or stone cistern in which the foot dc8 ' 8 

 of the screw is immersed, and from which the alum 

 liquors are raised, is shewn at O ; and at M there is an 

 ingenious contrivance for supplying the pivot regularly 

 with oil. The foot of the screw N is supported by a 

 step of bell metal, inserted into a piece of wood, the 

 socket for which is of cast iron wedged in the foot of 

 the screw, and well lapped in woollen cloth dipped in 

 rosin and tallow, to prevent the liquor from acting upon 

 it. The fall of water which drives the wheel is 9 feet, 

 and the water strikes the wheel 3 feet above the hori- 

 zontal axle ; the width of the mill course is 4| feet, the 

 depth of water 14 inches, and the aperture of the 

 sluice 2 inches. The water wheel revolves 12 times 

 in a minute, and the screw performs two revolutions 

 for one of the wheel, and consequently 24 revolutions 

 in a minute. The quantity of liquor discharged is 70 

 wine gallons ; but as the specific gravity of the fluid 

 raised is 1.065, the weight of the quantity discharged 

 in an hour is 17 tons. The pump is wholly built of tim- 

 ber, as the alum liquor acts upon the iron. Its total 

 length is 127 feet, and the height to which the liquor 

 is raised is = sin. 37 30' x 127 feet = 76 feet 9 inches. 

 The water wheel, besides driving the screw, moves two 

 pumps for lifting liquor to the height of 30 feet. The 

 pumps make each 2^ strokes for one turn of the wheel, 

 and the bore is 5| inches in diameter. 



A very ingenious double screw engine has recently Pattu's 

 been invented by M. Pattu, engineer of roads and brid- double 

 ges in the department of Calvados. It is represented s w en 

 in section in Fig. 3, and consists of two ordinary and 8 ' 

 concentric screws, one of which, AB, is long and nar- PI-ATE 

 row, and serves for the nucleus of the other, CD, which 

 is much wider and shorter. These two screws turn 

 round the axis in opposite directions, so that when one 

 of them appears to be moving upwards, the other ap- 

 pears to be moving downwards. The screw is inclined 

 35 to the horizon. The water from the stream MN is 

 introduced into the larger screw, and puts the whole in 

 motion, and the water, after its fall into OP, enters the 

 smaller screw, in which it is raised to the cistern at B. 

 When it is used for draining, and when the moving 

 power of the water can be applied at A, the small 

 screw serves to drive the larger one, which raises the 

 water to a height sufficient to carry it off, as shewn in 

 Fig. 4. Figures 5 and 6, shew other modes of applying Figs. 4, 

 this screw. Fig. 5 is the form used for raising water 6> 

 to irrigate high grounds, to fill the reservoirs of baths, 

 gardens, and manufactories. The large screw is here 

 the moving power. Fig. 6 is the form used for keep- 

 ing dry those places where foundations are building. 

 The large screw is here the mover. 



M. Eytelwein has shewn that the screw should al- 

 ways be placed so that only one half of a convolution 

 may be filled at each turn. When the height of the 

 water is so variable that this precaution is impractica- 

 ble, he prefers the water screw, although nearly one 

 third of the water in this case generally runs back, and 

 though it is easily clogged by accidental impurities in 

 the water. 



Fig. 7. shews the form of Archimedes's screw, as Fig T. 

 recommended by D. Bernoulli. 



These machines are particularly useful when the wa- 

 ter to be raised is not pure, but is mixed with gravel, 

 weeds, or sand, which could not be elevated by ordina- 

 ry pumps. For farther information on this subject, 

 See Vilruvius. Pitot, Mem. Acad. Par. 1736, p. 173- 

 Bernoulli, Hydrodynamica, Hennert Dissertation svr 



