For ten years Mr. Whitehouse has been brooding, as the faithfullest of mothers, over his theory, looking for a practical project to be hatched therefrom, but, as time passes, he begins to show signs of impatience, and fears lest his egg be addled. The possibilities as to what the chick may be when it appears, are set forth in Chapter V. of this paper, for I cannot but think that the egg is a good one. Mr. Whitehouse believes that in prehistoric times, before artificial works of control were made, the Nile flowed into and submerged the whole Fayûm, which was filled at high Nile, and that when the flood subsided, the return flow, that took place from the Fayûm to the Nile, prolonged the period of inundation by at least two months. He also believes that the river flowed in a single channel along the eastern desert. So far most of us who have our theories about the Fayûm travel together, with but small differences on the way. But after this our roads diverge, and each thinks the road he has selected leads to Lake Mœris. But they cannot all go there. Leaving prehistoric times, and coming to the period of ancient history, Mr. Whitehouse holds that there were two lakes. At first the northern lake, the Fayûm, was a lake and marsh serving as a backwater to the Nile, while the southern, the Wadi Raiân, was dry. So far I agree with him, but now we part company. Subsequently, he imagines, engineers of an alien race diverted the flood waters into the dry Wadi Raiân to the south-west and evaporation dried up the Fayûm, which was then irrigated by a system of canals. The Wadi Raiân basin becoming, full served as a reservoir, and was, according to Mr. Whitehouse, the “Mœridis Lacus” of Ptolemy. Later on, in 1890, Mr. Whitehouse explains his views in terms which are not quite in agreement with the foregoing, for he then supposes that the natural backwater of the Nile included the Fayûm and Wadi Raiân (with its minor basins Wadis “Safir” and “Lulu”) at one and the same time, and that these combined basins were filled to the level of high Nile, which he puts at R.L. 30·00. I think, however, his present views are, that at first the Wadi Raiân formed part of the Lake Mœris of Herodotus, of which the Fayûm was the main part; and that afterwards the Wadi Raiân alone formed the “Mœridis Lacus” of the Ptolemaic maps, the Fayûm having been brought under cultivation, after its waters had been dried up by evaporation. As the Wadi Raiân is the prominent feature of this theory, I will give here in full Colonel Western’s official description of it:—