This is a contrivance for raising water to some hight above the level of a stream. In the rim of a wheel turned by the stream a number of strong pins are fixed, to which buckets are suspended. As the wheel turns, the buckets on one side go down into the stream, where they are filled, and return full up the other until they reach the top. Here an obstacle is placed in such a position that it overturns the bucket, and the water is poured into a spout or convenient receptacle. It is evident that with this form of wheel the water can only be raised to the hight of the diameter of the wheel, and there is no doubt that it is a very rude contrivance. It is much used in Persia for the irrigation of the land, and very many of them may be" seen on the banks of the river Nile. Polarity.