1787. Dalziel's level (fig. 430.). This is an instrument of a very simple description, lately invented, for ascertaining the relative elevation of unequal surfaces. It consists of a wooden bar (a) with a foot at one end (b), and at the other another larger foot with a groove and scale (c), to which the bar is connected by a screw and nut. In using this instrument, two points of different altitude being chosen, the support of the bar (b) is to be placed on the higher, and (c) the foot of the scale on the lower; while the position of both is secured by a slight turn of the thumb-screw. The bar, being brought parallel to the horizon with the plummet (d), will indicate that the upper part of the scale is to be advanced, or the reverse, keeping its loot on the point of support, until some one of the graduations coincides with, or is visibly parallel to, the upper edge of the bar. The difference of altitude sought is seen in figures, without calculation. Any person that understands the use of a level will see a variety of levelling operations on a small scale that this implement is calculated to simplify: for example, if it be required to construct an inclined plane, rising an inch in a foot, the inner edge of the scale is to be brought six feet from the foot end of the horizontal piece, and rendered perpendicular to it, by making the graduated line at six inches coincide with the horizontal edge of the bar. Being fixed immovably by the screw in that position, the surface of the ground is then to be worked until the plummet hangs perpendicularly. The first six feet of the inclined plane having been thus constructed, other portions are to be taken successively throughout the remainder. If a plane of a different inclination is required, as of half an inch in a foot, the scale is to be shifted to three inches, and so on. (High. Soc. Trans., vol. v. p. 575.)
