NOTES ON THE PERCOLATION OF WATER.—SYSTEMS OF DRAINAGE OF CUTTINGS AND EMBANKMENTS IN DIFFERENT KINDS OF EARTH AND UNDER DIVERSE CONDITIONS.—THE CONSTRUCTION OF CULVERTS, PIPE-DRAINS, TRENCHES, DITCHES, AND CATCHWATER DRAINS. With respect to the percolation and drainage of water in cuttings and embankments, in cuttings the chief consideration is to gently extract and conduct the water so as to avoid any accumulation or localised flow beneath the original surface of the ground in order to prevent the surface water eroding the slopes or collecting or forming a course, saturating the ground outside them, and to ensure that the earth is not more charged with water than when in its normal condition; for, as soon as the state of absorption has reached that of dissolving or separating the particles, however fine, aqueous action is likely to produce slips, and a flow of water or vibration will supply the disturbing force necessary to commence a movement. In embankments one of the chief precautions is to obviate any flow of water upon or at a few feet beneath the land upon which an embankment has to be deposited, as it will disturb the feet of the slopes and the base, reduce the adhesion to and the friction of the tipped earth upon the ground and form a sliding surface. An accumulation of water upon the formation must be prevented, and, as in the majority of cases a railway or road is not level, any collection of water at the commencement of an incline or at a change of gradient should be provided against, and especially any localisation of flow down the slopes from the formation; the main point being to keep a cutting or embankment in a uniform state so that settlement is equable. By carefully watching the effect of heavy rain upon the slopes and the formation, the places where water amasses can be traced, and means used to restore the surface to the same condition as the other portions of a cutting or embankment. As water is the chief cause of slips, the friction and cohesion of earth being impaired and, perhaps, destroyed by it, it is obvious that at the time percolation, which varies greatly with the seasons, is at its maximum, _i.e._ when the earth becomes in a damp or wet state, slips are to be most expected, and particularly soon after the commencement of the wet season. It is known that upon the thawing of a heavy fall of snow, and of quickly succeeding and separate falls of snow, percolation is great; also after heavy and continuous rains, especially if the strata dip towards a river, and in the case of springs whose yield depends more upon percolation than the amount of rainfall, a wet winter will cause an increased flow some time after, when the earth may become saturated.