HYDRAULICS. 



found in the second lower bend u. In 

 the mean time, the lowest extreme end 

 of the tube will have made a second dip 

 into the water of the reservoir, and will 

 receive a second charge, which, in like 

 manner, will be transferred to u at the 

 next revolution, while the water lately 

 at u will be elevated \QW ; until at length, 

 when the cylinder has made as many re- 

 volutions as there are turns of the tube 

 round it, each lower bend will become 

 filled with water, whatever may be the 

 length of the cylinder y y ; and, as the 

 extreme upper end a of the tube be- 

 comes depressed, in each revolution, into 

 the situation of a lower bend, it will 

 there discharge its water into an ele- 

 vated cistern b placed to receive it. The 

 quantity of water raised by this machine 

 will depend upon flie capacity of the 

 screw-pipe, and the angle above the 

 horizon at which it is placed to work ; 

 but it will be seen by the figure, that 

 there is room to dispose several pipes 

 parallel to each other, round the same 

 cylinder, when they will all work simul- 

 taneously ; or the w r hole cylinder itself 

 may be made into a hollow screw, by 

 merely placing a thin, screw-formed 

 diaphragm or partition round its central 

 axis, which is the most usual form of 

 the machine in practice. On a small 

 scale, it may be constructed by wrapping 

 one or more flexible lead pipes round a 

 solid cylinder of wood, which forms a 

 useful machine for raising water to 

 small heights. It was formerly much 

 used ; but owing to its liability to be- 

 come choked by mud, weeds, and other 



impediments, and the great difficulty of 

 cleaning it out, it is seldom met with. 

 It has, from its specious appearance of 

 seeming to throw the entire weight of 

 water that it is raising upon its axles, 

 and the little friction with which these 

 may be made to move by friction rollers, 

 had astonishing powers ascribed to it ; 

 but if investigated, it will be found that 

 the water is merely made to flow up an 

 inclined plane ; and whether water, or 

 any other weight be drawn up a fixed 

 inclined plane, or it be stationary until 

 moved by an inclined plane being forced 

 under it, as is the case with the quanti- 

 ties of water contained in the several 

 bends v, u, w, x, &c. the mechanical 

 effort will be the same ; consequently, 

 this machine possesses no other mecha- 

 nical advantage over other construc- 

 tions of pumps, except that its motions 

 are attended by less friction than be- 

 longs to most of them. 



The principle of the Archimedian 

 Screw is occasionally adopted in the 

 wheel-form, by making the spokes or 

 radii hollow and curved, as shown at 

 c c c (fig. 4 .) : but in this way the wa- 

 ter cannot be raised higher than the 

 centre or axis of the wheel ; for the hol- 

 low spokes being open at the circum- 

 ference of the wheel, dip into the water 

 and receive their supply, which, from 

 the wheel's motion, and their peculiar 

 form, is carried to the axis ; which may 

 either be hollow to receive and cany 

 away the water, or a cistern may be 

 placed under it to receive the water from 

 the arms, 



