has a cast-iron cog-wheel at one end of its axis, as at r, r, which is one-fourth of the diameter of the correspondent cast-iron wheel, fixed on the nave ct the carriage-wheel, as in Fig. 1, f, f, so that the axis of the seed-box revolves 4 times during one revolution of the carriage wheels.
In the circumference of this wooden cylinder are excavated four lines of holes, consisting of six in each line, as at n, n, n, n, n, n. A similar line of excavations is made opposite to these, on the other side of the cylinder, and between these are two other rows of holes, amounting in the whole to twenty-four excavations in the wooden part of the axis beneath the seed-box, for the purpose of receiving and conveying the corn from the seed-cells into the flues o, o, i, i, (Fig. 2), while the axis is revolving: in which respect this improvement of Dr. Darwin bears some analogy to the original design of the celebrated Mr. Tull.
These excavations are one inch in length, half an inch in width, and three-eighths of an inch in depth, which dimensions are too large for any seeds employed at present in large quantities, except beans; but which may be contracted to any dimensions required, by moving the cylinder over the wooden one, as will be immediately explained.
Fig. 4, A, B, represents a tin cylinder one inch longer within, than the wooden cylinder on the iron axis at Fig. 3: it is 2 inches in diameter within, so as exactly to fit the wooden cylinder, which may slide within it about an inch backwards or forwards.—C, D, are two square sockets of tin, fixed on the ends of the tin cylinder to fit on the square part of the iron axis, passing through the wooden cylinder at l, l, Fig. 3, on which they slide one inch, as before.
The following directions for perforating the holes, both in the tin and wooden cylinders, which are mutually to correspond, Dr. Darwin recommends to be strictly attended to.
1. When the tin cylinder is soldered longitudinally, and one end of it is thus fixed, as at A, six holes ought to be made through it lengthwise on its four opposite sides; each hole must be exactly one half of an inch in width, and 5-8ths of an inch in length, which should be parallel to that of the cylinder. The centre of the first of these holes ought to be five inches distant from the closed end A; and that of the second hole, eight inches apart from the centre of the first; and the others in the same proportion, till six holes are made longitudinally along the cylinder. Another line of six similar holes is then to be made on the opposite side of the cylinder; and after that, two other such lines between the former; the number of holes amounting in the whole to 24, the dimensions of all which should be exactly observed, as well as their distances.
2. The wooden cylinder, fixed on the axis, is now to be introduced into that of tin, so as to leave the exact space of one inch void, at the closed end A; when the size of all these apertures through the tin cylinder (each of which is exactly half an inch in width, and 5-eighths of an inch in length), should be carefully marked with a fine point on the wooden cylinder, which ought not to be previously excavated.
3. The 24 holes, thus marked
