contained in the excavations of the cylinder beneath the seed-box, will be sown at 9 inches distance in each drill or furrow, while the plough is proceeding.
6. By Mr. Cooke's drill-plough, the quantity of seed sown on an acre is 6 or 7 pecks, that is, about half the quantity used in broad-cast sowing. If the wheat be exactly deposited in the drill, Dr. Darwin is of opinion that one bushel will be fully sufficient for an acre, as the rows are 9 inches apart from each other: for then 8 or 9 grains would be dispersed in every 9 inches of the drill furrow; namely, in every square of 9 inches surface of the land so cultivated.—This may be more clearly ascertained by the following data: Mr. Charles Miller, in the "Philosophical Transactions," vol. lviii. has calculated the number of grains in a bushel of wheat to amount to 620,000; Mr. Swanwick, of Derby, has lately computed them at 645,000; Dr. Darwin, therefore, concludes that a bushel, on an average, contains 635,000 grains of wheat. A statute acre comprises 4,840 square yards, each of which contains 16 squares of 9 inches: if 4,840 be multiplied by 16, the produce will be 77,440, which is the number of squares of 9 inches in such an acre. If 635,000 grains in a bushel be divided by 77,440, (the number of squares of inches in an acre), the quotient will shew, that somewhat more than 8 grains of wheat will thus be deposited in every 9 inches of the drills.
7. If 8 or 9 grains be dropped at the same time in one inch of ground, they will, if they all should grow together, be too numerous, and form a tussock; but, by making them slide down an inclined plane, from the seed-box to the coulters, as in the tin flues, which are crossed in order to lengthen them (Plate I. Fig. 2), some of the seeds will, by their friction while descending, be retarded more than others; and the 8 or 9 seeds will thus be scattered over the whole 9 inches of the drill; which renders this method of sowing far superior to that of dibbling; because, in the latter, all the seeds are dropped together.
8. When the holes in the wooden cylinder are entirely open, they are of a proper size for the sowing of horse-beans, or peas: when they are perfectly closed, there will remain a small niche at the end of the excavation in the wooden cylinder, nearest to B (Plate I. Fig. 4), for turnip, or other small seeds. For wheat, barley, and oats, a wooden wedge ought to be made exactly of the same shape as the area of the hole, which the director of the plough requires, who will insert it occasionally in the holes, when he turns the screw at the end of the cylinder, in order to enlarge, or reduce them, according to those dimensions. On these wedges ought to be written, with white paint, wheat, barley, oats, &c. which will considerably facilitate the accommodating of the size of the excavations to each kind of grain; and which may be altered, if requisite, to suit larger or smaller seeds of the same species.
9. In some drill-ploughs, for instance in Mr. Cooke's, there is some additional machinery for drawing a line, while the plough proceeds, in which the wheel that is next to the last-sown furrow, may be directed to pass at a proper distance from, and parallel to it. This, however, may be effected,
