Plough, one of the best-known and universally-used instruments of agriculture, though much changed from its primitive formation, still retains its original essential features. It appears to date from the first period at which man conceived the idea of utilising a second person - whether human or not - to aid him in turning up the ground. The earliest form of plough seems to have been a forked bough, a short and sharpened end of which was drawn through the ground, while a kind of handle fixed in the rear enabled someone to guide it from behind. Such a plough was in use in ancient Egypt, and was early introduced into Greece, while the Romans were not slow to produce a much more elaborate contrivance. The Roman plough is very fully described by Virgil in his Georgics. The essentials of the plough are - (a) the beam to which the horse is fastened, and which is lengthened backwards into one handle, to which the other handle is attached at an angle, and fastened by one or more cross-pieces; (b) the coulter, a vertically-fixed blade which cleaves the earth in a perpendicular direction; (c) the share, which cleaves it in a horizontal direction; (d) the mouldboard, which turns over the excavated soil. Few implements have undergone more improvements, some of which are the substitution of iron for wood and the addition of wheels for greater ease and uniformity of work. The huge prairie-farms of America have given a great impetus to the improvement of ploughs, and it is in that country that the greatest variety is to be found. One of the most useful of these varieties is the double gangplough. In this there are two shares set parallel to each other, but one in rear of the other, so as to make two furrows, and each of these shares has a removable point, which can be changed when it wears down. To the front part of the beam is fixed a single wheel, which can be adjusted by an arc-shaped lever, so as to regulate the depth of the furrow. The application of steam-power to ploughing has made comparatively little progress, though it has been employed with advantage in cultivating the wild lands in the north of Scotland, on the huge farms of America, and elsewhere where ploughing on a large scale is needed. The most ordinary form of steam-plough is one which is worked by a stationary engine at one end of the line and a drum secured at the other end, the two working an anchored cable and the plough, which turns several furrows, passing to and fro from one to the other, the points of appui being shifted as the work proceeds. The plough itself forms an obtuse angle, the exterior sides of which are provided with shares, and the one side is in the air while the other is at work. Each side of it is fitted with a seat and a steering-rod for the man who accompanies the plough.