It is believed, however, that generally, it will be found true economy, to procure the aid of an experienced engineer, if convenient, to lay out the work at the outset. Certainly, in most cases, some skill in the use of levelling instruments, at least, is absolutely essential to systematic work. No man, however experienced, can, by the eye, form any safe opinion of the fall of a given tract of land. Fields which appear perfectly level to the eye, will be found frequently to give fall enough for the deepest drainage. The writer recently had occasion to note this fact on his own land. A low wet spot had many times been looked at, as a place which should be drained, both to improve its soil, and the appearance of the land about it; but to the eye, it seemed doubtful whether it was not about as low as the stream some forty rods off, into which it must be drained. Upon testing the matter carefully with levelling instruments, it was found that from the lowest spot in this little swamp, there was a fall of seven and a half feet to the river, at its ordinary height! Again, there are cases where it will be found upon accurate surveys, that the fall is very slight, so that great care will be requisite, to lay the drains in such a way that the descent may be continuous and uniform. Without competent skill in laying out the work, land-owners will be liable not only to errors in the fall of the drains, but to very expensive mistakes in the location of them. A very few rods of drains, more than are necessary, would cost more than any charge of a competent person for laying them out properly. Again, experience gives great facility in judging of the underground flow of water, of the permeability of soil, of the probability of finding ledges or other rock formation, and many other particulars which might not suggest themselves to a novice in the business. The laying out of drains is important, not only with reference to the work in hand, but to additional work to be executed in future on adjoining land, so that the whole may be eventually brought into one cheap and efficient system with the smallest effective number of drains, both minors and mains, and the fewest outlets possible; with such wells, or other facilities for inspection, as may be necessary.