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accumulation of weeds or other extraneous substances amongthe tines, or by the harrows riding on each other. Threeharrows to one driver is certainly the most convenient andeconomical method, as these entirely cover one ridge of eigh-teen feet broad at two times, without wasting any part of thelabour.
There are a variety of harrows for different purposes. Theheavy break-harrow, drawn by two horses, is used for redu-cing strong land, or soil which is much matted with the rootsof couch grass. The ordinary harrows, each of which isdrawn by one horse, serves for oovering in the seed, and formost other farm purposes. Much lighter harrows are em-ployed in covering grass seeds, among grain which has al-ready sprung above ground. These different kinds of har-rows, as commonly used in Scotland , are described in a pre-ceding part of this Report.
The operation of harrowing is denominated single time,double time, and double-double according as the ground isgone over once, twice, or four times ; and, as it is usual tooverlap each of these successively in some degree at theiredges, they are then called close single, close double, &c. re-spectively. Harrowing is likewise called end-long or across,according as the harrows move in the direction of the ridges,or transversely. Some farmers prefer finishing off a field bycross harrowing, especially in heavy land, under the idea offacilitating the descent of surface-water from the crowns ofthe ridges to the inter-furrows.
A pair of harrows, of the ordinary construction, completelycovers six feet of ground, which is equal to eight furrow-slicesof nine inches each. Consequently one man and a pair of hor-ses, moving at the ordinary rate of the plough, as estimated inthe former section, ought to single eight times as much landas they can plough in a day of nine hours. As harrowing is amuch easier work, and the horses consequently step out bet-ter and more nimbly, one quarter may be added on that ac-