2. The medium canals, which irrigate between R.L. 18·00 and 10·00 or thereabouts. 3. The long ravine canals, which carry water to the distant parts of the Fayûm below contour R.L. 10·00. In a lawless province like the Fayûm, such an arrangement of canals is of great assistance in the equal distribution of water to all parts of the province. The long canals of class 3 are, in their upper reaches, so far below the cultivated surface of the soil, that no crop-owner of the first and second plateaux would attempt to irrigate from them except by means of water-wheels, which have to be regularly licensed. The canals of the 2nd class are intermediate in level and length between the first and third, and do not conveniently irrigate, except at some considerable distance from their heads. There is a further advantage gained by the water of the long canals falling at once to low levels at their commencement. Along the margins of the Bahr Yûsuf and round about Medineh is a considerable area of valuable land above the highest level reached by the water in the parent canal. To irrigate this, water is lifted in pitchers fastened to the side of the outer edge of undershot wheels, which are turned by the force of the water descending to the low-level beds of the ravine canals. These wheels turn day and night without ceasing, so long as there is sufficient water. A head of 25 centimetres is sufficient to turn an ordinary wheel which lifts the water about 2 metres, but when greater heads are obtainable, water is lifted in this way as much as from 4 to 6 metres (Plate IV.) A fall of 80 centimetres will work two wheels, one behind the other, which lift the water 5 metres. The channel, carried by the imposing looking aqueduct of Plate IV., is only 40 centimetres wide by 30 centimetres high, the whole thickness of the aqueduct being only 85 centimetres. The expense, incurred in building it, points to the value of a constant stream of water raised in this manner. There are two kinds of wheels used, one in which the water lifted is contained in earthenware jars fastened to the side of the wheel near its outer edge, the arrangement of which is shown by the drawing, reproduced from Willcocks’ ‘Egyptian Irrigation’ (Plate V.) The other kind of wheel, called a _tabût_, has a hollow chambered tube of square cross-section forming its circumference, the holes to admit water into each chamber being made in such a position that the water, which enters the chamber when submerged, does not commence to flow out again, till the chamber approaches the highest point of its path. Below the point, at which the flow out commences, a trough is placed to catch the water.