principles, or directions, Dr. Darwin observes:
1. That in constructing tin and wooden cylinders beneath the seed-box, another small improvement may become necessary in sowing very small seeds, namely, when the screw at the end A, is turned, so as to contract all the excavations of the wooden cylinder, its surface will become bare for the space of one inch from the end of each excavation towards the end B, (Plate I. Fig. 4), without being covered by the tin cylinder. On these exposed parts, which will be one inch long, and half an inch wide, some seeds may accidentally stick, and evade the brushes which are to prevent them from passing, while the cylinders revolve. To remedy this inconvenience, when the wooden cylinder is placed within the tin one, in such a direction that all the holes are completely open, Dr. Darwin recommends a piece of the tin cylinder, about an inch and an half in length, and half an inch in width, to be cut out from the extremity of each hole next to the end B, and such piece to be fixed by a few sprigs on the wooden cylinder, exactly in the same place it covered previously to its being cut out of the tin one; by which means, when the tin cylinder is afterwards pushed forwards, by turning the screw at its end, so as to contract the excavations of the wooden cylinder beneath, its bare parts will be an inch and a half distant from the extremities of the excavations next to the end B; and thus will not pass under the brushes: consequently no small seeds can be lodged in them.
2. Some kind of iron staple ought to be fixed on the outside, at each end of the seed-box, to catch hold of the two springs at d, d, (Plate I. Fig. 1), when the hinder part of the carriage is elevated by the man guiding it, in order to suspend the coulters out of the ground, and to connect the hinder part of the machine with the shafts before: so that, when turning at the ends of the lands, or passing to or from the field, the wheels may not deviate from the joint z, at the centre of the axie-tree, but may follow in the same lines as the shafts.
3. The seed-box should likewise be supported on erect iron pins, passing through staples of that material; with a lever under the end of it, next to the wheel r, r, (Plate I. Fig. 3), in order to lift easily that end of the seed-box, about an inch high, and to raise the teeth of the iron cog-wheel on its axis out of the teeth of the correspondent iron one, on the nave of the carriage-wheel.
4. The construction of the coulters winch make the drills, and of the rakes, by which they are filled after the seed is deposited, and also of the hoes, are not delineated; as they resemble those employed by persons practising the drill husbandry, and which we have already described, when treating of Mr. Cooke's patent machine.
5. When the lower ends of the seed-flues are placed through the holes in the coulter-beam (Plate I. Fig. 1), at the distance of 9 inches from each other, the rows of wheat or beans will be 9 inches apart: hence, as the wheels of the carriage are 4 feet in diameter, and therefore move about 12 feet at every revolution; and, as there are 4 excavations round the axis of the seed-box, which revolve 4 times to one revolution of the carriage-wheels, consequently the seeds
