*Grading the Bottoms.*—The next step in the work is to grade the bottoms of the ditches, so as to afford a bed for the tiles on the exact lines which are indicated by the figures marked on the different stakes. The manner in which this is to be done may be illustrated by describing the work required for the line from *C10* to *C17*, (Fig. 20,) after it has been opened, as described above, to within 2 or 3 inches of the final depth. A measuring rod, or square, such as is shown in Fig. 28,(18) is set at *C10*, so that the lower side of its arm is at the mark 4.59 on the staff, (or at a little less than 4.6 if it is divided only into feet and tenths,) and is held upright in the ditch, with its arm directly over the grade stake. The earth below it is removed, little by little, until it will touch the top of the stake and the bottom of the ditch at the same time. If the ground is soft, it should be cut out until a flat stone, a block of wood, or a piece of tile, or of brick, sunk in the bottom, will have its surface at the exact point of measurement. This point is the bottom of the ditch on which the collar of the tile is to lie at that stake. In the same manner the depth is fixed at _C11_ (4.19,) and _C12_ (4.41,) as the rate of fall changes at each of these points, and at _C15_ (3.89,) and _C17_ (4.17,) because (although the fall is uniform from _C12_ to _C17_,) the distance is too great for accurate sighting. [Illustration: Fig. 29 - BONING ROD.] Fig. 29 - BONING ROD. Having provided _boning-rods_, which are strips of board 7 feet long, having horizontal cross pieces at their upper ends, (see Fig. 29,) set these perpendicularly on the spots which have been found by measurement to be at the correct depth opposite stakes 10, 11, 12, 15, and 17, and fasten each in its place by wedging it between two strips of board laid across the ditch, so as to clasp it, securing these in their places by laying stones or earth upon their ends. As these boning-rods are all exactly 7 feet long, of course, a line sighted across their tops will be exactly 7 feet higher, at all points, than the required grade of the ditch directly beneath it, and if a plumb rod, (similar to the boning-rod, but provided with a line and plummet,) be set perpendicularly on any point of the bottom of the drain, the relation of its cross piece to the line of sight across the tops of the boning-rods will show whether the bottom of the ditch at that point is too high, or too low, or just right. The manner of sighting over two boning-rods and an intermediate plumb-rod, is shown in Fig. 31. [Illustration: Fig. 30 - POSITION OF WORKMAN AND USE OF FINISHING SCOOP.] Fig. 30 - POSITION OF WORKMAN AND USE OF FINISHING SCOOP.