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mechanical advantage to be gained by it. The application of the tooth and pinion is exemplified in the representation of a rice-mill moved by water, at page 37 of Barrow's Travels. They seem to understand, in practice at least, that power and velocity vary inversely in machinery; as, for instance, that power is gained, or time, according as the moving force is applied either to the circumference, or the axis of a wheel.

It is remarkable that they should seem always to have possessed that particular application of the principle of the wheel and axle, by which the greatest power is attained within the least space; and, at the same time, with the greatest simplicity, as well as strength of machinery. The cylinder ab consists of two parts of unequal diameter, with a rope coiled round both parts in the same direction,

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the weight to be moved being suspended by a pulley in the middle. Every turn of the cylinder raises a portion of the rope equal to the circumference of the thicker part, but at the same time lets down a portion equal to the circumference of the thinner; and, as the weight is suspended by a pulley, it rises at each turn through a space equal to only half the difference between the span of the thicker and thinner parts of the cylinder. The action of the machine, therefore, is very slow; but the mechanical advantage is great in proportion, or, in other words, "power is gained at the expense of velocity," according to an invariable law of mechanics."

The over-shot water-wheel is used commonly in cornmills, wherever the nature of the country affords streams available for the purpose. In cottages, a domestic mill was frequently seen by our embassies, composed of two

circular stones put in motion by a single man or boy, or sometimes an ass or mule, the power being applied at the end of a lever fixed in the uppermost stone.

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The juice of the sugar-cane is expressed in mills similar to those used in India, according to the description of Dr. Buchanan. It consists of two upright cylinders, which are put in motion by a buffalo yoked to a beam passing from

Rice Mill.

the top of one cylinder. The mill is fed by introducing the cane between the rollers, by which it is crushed and carried over to the other side. The expressed juice runs through a channel below into a large reservoir, whence it is transferred to boilers, and, being there sufficiently inspissated, is sent in tubs to the refiners. In the above instance the mechanism might be evidently economised and improved by causing the cylinder, which communicates motion, to turn two others instead of only one. This is known to be the practice in our West Indian colonies. The Chinese excel in their contrivances for raising water in the irrigation of their lands, and it is probable that these inventions are nearly as old as their husbandry itself. One of them is an ingenious species of chain-pump, which we give here, as it is well described and figured in Staunton's Embassy.* The pump consists, in the first place, of a hollow trough or trunk, of a square make. Flat and square pieces of wood, corresponding exactly to the dimensions of the cavity of the trunk, are fixed to a (jointed) chain, which turns over a roller or small wheel placed at each extremity of the trunk. The square pieces of wood fixed to the chain move with it round the rollers, and lift up a volume of water equal to the dimensions of the hollow trunk. The power used in working this machine is applicable in three different ways: if the machine be intended to lift a great quantity of water, several sets of wooden arms are made to project from various parts of the lengthened axis of the roller, over which the chain and lifters turn. These arms are shaped like the letter T, and made round and smooth for the foot to rest upon. The axis turns upon two upright pieces of wood, kept steady by a pole stretched across them. The machine being fixed, men treading upon the projecting arms of the axis, and

* Vol. ii. p. 480.

supporting themselves by the beam across the uprights, communicate a rotatory motion to the chain, the lifters attached to which draw up a constant and copious stream

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of water. This manner of working the chain-pump is illustrated in the preceding cut, and is applied principally to raising water to small heights from rivers or canals: frequently to pumping out the holds of their merchant-vessels.

"Another method of working this machine," continues Staunton, "is by yoking a buffalo or other animal to a large horizontal wheel, connected by cogs with the axis of

* These lifters go up through the inside of the trough, and come down again above it, in a reversed position.

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the rollers over which the lifters or boards turn. This mode was observed by the travellers only at Chusan. small machine of this kind (in the third place) is worked merely by the hand, with the assistance of a trundle and simple crank, such as are applied to a common grindstone, fixed to one end of the axis of the chain-pump. This last method is general throughout the empire. Every labourer is in possession of such a portable machine—an implement to him not less useful (in rice cultivation) than a spade to an European peasant. The making of those machines gives employment to a great number of artificers.”

But by far the most ingenious and useful contrivance for irrigating lands is that which our embassies met with on the river that flows down, with a rapid stream, from the ridge of mountains bounding the Canton province on the north (and called the Meiling pass), towards the Poyang lake and the Yang-tse-keang. The velocity of the current has worn away the banks, which consist of a loose soil, to the depth in some places of thirty feet and more. Here the chain-pump already described becomes altogether unavailable, as the weight and pressure of a column of water of that height, and the friction of the length of chain required, put it out of the question. But Chinese ingenuity has converted the strength of the stream into a means of overcoming the very difficulties which it originally occasioned; and one is at a loss which most to admire, the cleverness and efficiency, or the cheapness and simplicity, of the contrivance. The wheel, which is turned by the stream, varies from twenty to thirty feet or more in height, according to the elevation of the bank; and, when once erected, a constant supply of water is poured by it day and night into a trough on the summit of the river's side, and conducted in channels to all parts of the sugar plantations which there chiefly occupy the lands.

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