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This engraving represents a simple instru ment recently designed by W. Gillespie, of Torbanehill, Linlinthgowshire, Scotland, for the purpose of facilitating the formation of a drain to carry off the water from the foundations of his house. The circumstances of the case demanded especial exactness and uniformity of slope, and the quantity of water to be removed was very considerable ; for on goi.ig down 2j feet, it was found that the house was actually standing on a hydrostatic bed. This accumulation of moisture was to e discharged by a drain, sunk direct 5i feet at the very door-step. Commencing at such a depth, it was, of course, essential to guide the slope with accuracy, so as to preserve the outfall at the other extremity; and' it was evident that any misdirection might endanger the house by causing the unpleasant result ef back-water. During the progress of the work, Mr. Gillespie being dissatisfied with its appearance, conceived the idea of this apparatus. The instrument is nothing more than a parallelogram of timber and a plummet, in combination. The engraving shows it as pointing out the slope of a line ot drain pipes. From the nature ot the parallelogram, ABC D, it is obvious that the top, A D, must be parallel with the base, ? C; and to show the deviation of the upper of these coinciding slopes from the level, the instrument is provided with the means of determining what the j true level is. It has a duplicate top, A E, ' hinged to the angle, A. The other extremity j of this duplicate top being a little protracted j is formed into the well-known T-square by ( insertion through a slit (in which a slight , range is given to accommodate the working ; of the implement) of a depending limb, ? F, ' at right angles to ? ?. ? F is graduated ! downwards for several inches in sixteenths of j an inch. The face of the depending limb is j likewise grooved for the reception of a plum- j met, G H, or pendulum of wire playing upon i its graduated front. A quadrant, K., moved by turning the ratchet-pin, L, is employed to elevate or depress the duplicate top spar, A j E, until the plummet rests from its oscilla- j tions, in exact accordance with a vertical line ! drawn from the face of the T-square. This shows the top spar, A E, to have been adjusted to the proper level. On the other side of the implement, behind the ratchet pin, will be found an inverted pinch or pressing screw, by turning which backwards, the implement is set, and the square top fixed on the horizontal or true level. The limb, A E, being now upon the level, whilst the limb, A D, still continues to indi- i cate the slope, the difference intervening betwixt the level and the slope is necessarily denoted on the graduated scale, which being fixed upon the inner edge ot the plummet style, i measures the exact rate of slope to which the instrument is applied. I J is a light [telescope for extending the range of the level. By means of it, the out fall or depth of slope can be determined throughout any distance within the scope of vision, and the heights of objects may be measured where their distances can be ascertained. ? ? is an extra base bar, protracting the slope, and giving the rate of it with grmter certainty of precision. We learn by the " Glasgow Practical Mechanic's Journal," in which the above instrument was first illustrated, that it is now in established use for road and drain making.
