only a wooden or iron bar, B, B, (Fig 3), about 2 inches broad, 4 feet 8 inches long, and exactly 3-eighths of an inch thick. Through this bar 6 holes are perforated, marked e, e, e, &c. each of which is exactly one inch in length, half an inch in width, and 3-eighths of an inch in depth, which is the same as the thickness of the bar. The centres of these holes are exactly 8 inches distant from each other, corresponding to the holes at the bottom of the seed-box, over which it is made to slide backwards and forwards in a groove. By this sliding motion, it passes under stiff brushes which are placed over it on each end of the holes, at the bottom of the seed-box, and strickle off the grain, as the holes in the sliding-bar pass under them, which thus distribute the quantity with considerable accuracy.
In order to increase, or diminish, the proportion of grain to be delivered, the slider is covered with a tin-case, C, C, (Fig. 4,) which is perforated with six holes, corresponding with those in the slider: instead, however, of the bit of tin being cut out the full length of the hole, part of it is left at the end equal to the thickness of the slider, and is bent down, after the slider is put into the case, in the same manner as the tin cylinder in the preceding machine. This case is moveable about one inch, backward and forward, by turning the finger-screw s (Fig. 4 and 5), by which the holes are enlarged, or diminished, for the purpose of adapting them to various sorts of grain, or different quantities of the same sort, exactly as in the tin and wooden cylinders in Plate I.—The slider is moved forwards by a bent iron pin, h, attached to it, which passes into a serpentine groove, Y, (Fig. 5), fixed to the nave of the wheel: it is likewise moved backwards by a steel spring at the other end of the seed-box, but which is not delineated in the Plate.
Fig. 5, is a bird's-eye view of the parts before described:—E, E, the seed-box divided into cells or compartments, by the partitions d, d, d.—c, c, c, the slider, with part of the apertures seen just appearing from under the brushes.—X is the axis of the wheel.
Fig. 2, represents a side view of one of the six bridges lying over the holes at the bottom of the seed-box, on each side of which the brushes are fixed, which strickle the holes when full of corn, while the bar slides backwards and forwards. The simplicity of this slider at the bottom of the seed-box, Dr. D. observes, may be, in some instances, greater than that of wooden and tin cylinders in his machine, as Mr. Swanwick's has only six holes for distributing the quantity of corn, whereas the former has twenty-four. In other respects, it is, perhaps, more complicated; as twelves brushes are used, one on each side of the six holes, whereas there are only six brushes rubbing on the tin cylinder in the former machine. The reciprocating motion of this slider must be quick, as it necessarily acts once every time the circumference of the carriage-wheel passes nine inches forward, which may not be so easy to execute as the cog-wheel, with the uninterrupted movement of the axis and cylinder in the preceding machine.
Lastly, Dr. Darwin concludes with remarking, that the facility of adapting the holes to the dimensions required in both machines, and the
