The output of wells is determined in a somewhat rough and ready manner by measuring the depth of water passing over a weir fixed in the stream. It is reckoned in qirats, one qirat being a water-section of 64 square centimetres; from some test observations in Kharga Dr. Ball deduced the average value of a qirat, as measured in that oasis, as 230 litres a minute. The total water-output in Dakhla (1096 qirats) may thus be taken as approximately representing a discharge of 132 million cubic metres per annum, and taking the cultivated lands as 25,500 acres the duty is 6,130 acres per cubic metre per second. That the water-supply could be largely increased, and the limits of cultivation greatly extended, admit of no doubt, but with the free hand accorded the natives during the last few decades a considerable amount of damage has been done throughout the oasis by the injudicious sinking of wells. Promiscuous boring is fatal, and strict and efficient control of all boring operations imperative. Considering the number of wells abandoned owing to a slight fall in the water-level having caused them to cease running at the surface, the importance of lifting appliances, in the shape of shadûfs, saqias, or windmills, is evident, but until a few years ago the oasis was destitute of such appliances; a number of saqias have recently been fixed in the village of Mushîa and have met with success, but it is not an easy matter to persuade the inhabitants to have recourse to lifting appliances of any description. Some of the Dakhla wells are of considerable depth; Bir-el-Dinaria, the most northerly in the oasis, is 144 metres deep and its water emerges with a temperature of 39·5° C. The best wells yield 9 or 10 qirats, though before the modern boring operations the output of some was as much as 16. The terms ‘artesian’ and ‘thermal’ may fairly be applied to the Dakhla wells, and it is noteworthy that the temperatures as a whole increase from south to north. The thermal character of the springs may be considered to be due to the great depths from which the water is derived, the actual temperature at the point of exit being dependent on local conditions, such as the depth of the well and the rate at which the water finds its way to the surface. It is probable that the water-bearing table has its outcrop in the rainy regions of Darfur, although some of its water may be derived by direct infiltration from the Nile in its upper reaches. [Illustration: PLATE XXI. THE EGYPTIAN OASES Scale 1 : 6.000.000]