much on an edge, the plough may be adapted to either purpose with the utmost facility, by this improvement of the mould-board. When the moveable parts, above alluded to, are screwed outwards, a proportionate convexity or elevation will be left at the base of the furrow; and thus more earth will be exposed for covering the seed. Lastly, as the part of the mould-plate, marked with the dotted lines C C, is most liable to wear off by repeated friction, Lord Somerville directs it to be made twice as thick as the other parts of the plate; viz. double "the thickness of a new crown-piece," or about one-fourth of an inch; in which case it will remain unimpaired, nearly as long as the whole of the machinery.
The chief improvement made by Lord Somerville being in the mould-plate of his useful plough, we have subjoined two figures, representing its internal strudure, in different points of view, by which its mechanism may be more clearly understood.
a, a, a, the screws that advance or withdraw the moveable mould-plate.
b, b, the moveable plate.
c, c, ribs, which serve to strengthen the plates.
d, grooves, sunk in the mould-board for the reception of the ribs, when the mould-plate is withdrawn.
Lord S. observes, that "the principle of this moveable plate may not at first catch the attention of every reader;" but it deserves to be generally adopted, and has indeed met with strong advocates in ploughmen; for it not only relieves their right arm of considerable labour, that must otherwise be performed in wedging and hammering mould-plates; but much exertion is also saved to the right leg, in attempting to tread those furrows flat, which had been left on an edge by the plough. Lastly, these plates are indispensably necessary, in order to qualify two-furrow ploughs for all broad work, and particularly breaking up leys; and such implements ought (in the technical phrase) to work on their own base, close at heel; as otherwise the furrow will be irregularly laid; and they will be immediately "thrown out of work."
Before we conclude the account of this valuable contrivance, it is but justice to state the result of a trial made at Kew, in March 1799, on His Majesty's Farm, in conse-
