“Dateram” is, as the late Dr. Barth, informed me, the Bornu name for a most excellent African contrivance, used in some parts of the Sahara desert, by means of which tent-ropes may be secured, or horses picketed in sand of the driest description, as in that of a sand dune, whence a tent-peg would be drawn out by a strain so slight as to be almost imperceptible.  I have made many experiments upon it, and find its efficiency to be truly wonderful.  The plan is to tie to the end of the tent-rope, a small object of any description, by its middle, as a short stick, a stone, a bundle of twigs, or a bag of sand; and to bury it from 1 to 2 feet in the loose sand.  It will be found, if it has been buried 1 foot deep, that a strain equal to about 50 lbs. weight, is necessary to draw it up; if 1 1/2 feet deep, that a much more considerable strain is necessary; and that, if 2 feet deep, it is quite impossible for a single man to pull it up.  In the following theoretical case, the resistance would be as the cube of the depth; but in sand or shingle, the increase is less rapid.  It varies under different circumstances; but it is no exaggeration to estimate its increase as seldom less than as the square of the depth.  The theoretical case of which I spoke, is this:—­Let x be part of a layer of shingle of wide extent:  the shingle is supposed to consist of smooth hard spherical balls, all of the same size.  Let s be a dateram buried in x; and T the string to which it is tied.  Now, on considering fig. 2, where a series of balls are drawn on a larger scale and on a plane surface, it is clear that the ball A cannot move in any degree to the right or the left without disturbing the entire layer of balls on the same plane as itself:  its only possible movement is vertically upwards.  In this case, it disturbs B1 and B2.  These, for the same reason as A, can only move vertically upwards, and, in doing so, they must disturb the three balls above them, and so on.  Consequently, the uplifting of a single ball in fig. 2, necessitates the uplifting of the triangle of balls of which it forms the apex; and it obviously follows from the same principle, that the uplifting of S, in the depth of X, in fig. 1, necessitates the uplifting of a cone of balls whose apex is at S. But the weight of a cone is as the cube of its height and, therefore, the resistance to the uplifting of the dateram, is as the cube of the depth at which it has been buried.  In practice, the grains of sand are capable of a small but variable amount of lateral displacement, which gives relief to the movement of sand caused by the dateram, for we may observe the surface of the ground to work very irregularly, although extensively, when the dateram begins to stir.  On the other hand, the friction of the grains of sand tends to increase the difficulty of movement.  The arrangement shown in the diagram, of a spring weighing-machine tied to the end of a lever, is that which I have used in testing the strain the dateram will resist, under different circumstances.  The size of the dateram is not of much importance, it would be of still less importance in the theoretical case.  Anything that is more than 4 inches long seems to answer.  The plan succeeds in a dry soil of any description, whether it be shingly beach or sand.