112
[Book I.
THE NOKIA OK EGYFTIAN WHEEL.
The tympanum has been described as an assemblage of gutters, andthe Noria may be considered as a number of revolving swapes. It con-sists of a series of poles United like the arms of a wheel to a horizontalshaft. To the extremity of each, a vessel is attached, which fills as itdips ]into the water, and is discharged into a reservoir or gutter at the upper ;part of the circle which it descrihes. See No. 47. Hence, the formetraises water only through half a diameter, while this elevates it thronglia whole one, The idea of thus connecting a number of poles with theirbuckets, must have early occurred to the agricultural machinists of Asia .The advantages of such an arrangement being equally obvious as in the ,tympanum. The means that naturally suggested themselves, of strengtli-ening a number of poles thus arranged, gradually brought these machinesinto the form of wheels. Sometimes, a rüde ring was formed, to whichthe exterior ends were secured; at others, disks of plank were adopted,and the vessels were attached either to the sides or rim, and sometimes toboth.
The Chinese make the noria, in what would seem to have been its pri-mitive form; and with an admirable degree of economy, simplicity, andskill. With the exception of the axle and two posts to Support it, thewhole is of bamboo, and not a nail used in its construction. Even thevessels, are often joints of the same, being generally about four feet longand two or three inches in diameter. They are attached to the poles byligatures at such an angle, as to fill nearly when in the water, and to dis-charge their contents when at, or near the top. See No. 48.
The periphery of the wheel is composed of three rings of unequal di-ameter, and so arra,nged, as to form a frustrum of a cone. The smallestone, to which the open ends of the tubes are attached, being next the bankover which the water is conveyed. By this arrangement, their contentsare necessarily discharged into the gutter as they pass the end of it.When employed to raise water from running streams, they are propelledby the current in the usual way—the paddles being formed of wovenbamboo. The sizes of these wheels, vary from twenty to seventy feet m