Beadnell’s observations of wind-direction[57] and from the fact that the scoring of the limestones in the Libyan Desert by wind- borne sand coincides in direction with the lines of dunes.[58] Thus I suggest that while the extension of the lines of dunes southwards is purely the result of the prevailing north-north-west wind, their clean- cut character and narrow width is the consequence of lateral attraction by the dunes themselves on the flying electrified particles of sand. If the hypothesis I have ventured to put forward is regarded as likely to furnish the true explanation for the formation of the lines of dunes, I hope that someone possessing the necessary skill in electrostatic measurement will put it to a crucial test, by carrying out observations on and near the dunes themselves. If a number of flying sand-grains could be caught from different levels in an insulated metallic receiver connected to an electrometer, the readings of the electrometer would enable the potentials to which the grains were charged at different levels to be calculated, provided the electrostatic capacity of the receiving system and the number and diameter of the grains giving up their charge were measured. Allowance would, of course, have to be made for any electrification of the receiver by the air, or by uncaught sand- grains, as well as for losses by imperfect insulation of the collecting system. In a preliminary experiment of this kind which I made in Cairo during a sandstorm, leakage from the electrometer was found to be so great as to vitiate any attempts at accurate measurement; but I think this particular difficulty could be overcome with a specially designed apparatus, or that at least the leakage could be measured and allowed for. The taking of observations of any kind in dune areas during windy weather is a most difficult and trying operation, and commonly means, in addition, a sojourn of some weeks in isolated and otherwise uninteresting areas. But the advent of the motor-car has so greatly facilitated communication in the deserts that difficulties of access are now not so great as they used to be; the south end of the 35-kilometre line of the Kattania Dunes, for instance, about 90 kilometres west- south-west of Cairo, which would form an excellent site for detailed observations, can now be reached by a four or five hours’ car journey from Cairo instead of the several days’ journey by camel which was formerly necessary. 12. _The Distribution of Stone Implements._