The scythe was a distinct improvement over the sickle. It enabled a man to use two hands at the work of reaping instead of one. It provided a much longer and heavier blade, and hence a much broader swath was cut at each stroke. A distinctly American improvement on the scythe is the grain cradle, consisting of a set of fingers above the blade which catch the grain and lay it in a swath at the end of the stroke. This important improvement rapidly spread to all parts of the world and is still used to-day where it is impracticable to use a mechanical reaper. It is claimed that one man can cut and bind more grain with the cradle than three men could with the sickle. EVOLUTION OF THE PLOW The plow has undergone important developments in comparatively recent years. Wooden plows were still in use in America in Revolutionary times; usually the point was shod with wrought iron. However, these wooden plows speedily gave way to metal when iron came to be manufactured in considerable quantity in this country. A plow has to contend with two conditions of service that apparently conflict with each other. The constant friction of the soil against the blade tends to wear it away very rapidly, hence a very hard surface is requisite. On the other hand, the plow is apt to encounter buried stones and rocks which will shatter it unless it is soft. The problem then is to make the plow both hard and soft. The chilled iron plow was invented by Oliver, in 1855, to meet the first condition. When molten iron is poured into an iron mold the surface that comes into contact with the mold is suddenly chilled, producing a very hard surface that takes a good polish. This effect is accentuated by using a hollow mold through which water is circulated. The hard surface of the chilled iron wears well in sandy and gravelly soil, it does not rust deeply, and it clears well in sticky soil. However, it is very brittle and is liable to break if struck a sharp blow. A more recent improvement is the soft-center steel plow. This is both hard and soft. It is composed of three layers of metal; the outer layers are of hard cast steel and the center one of soft steel. These metal layers are heated to a welding heat and then rolled together, producing a plow that has a hard outer wearing surface and at the same time is tough because the center layer of soft steel acts as a cushion to absorb sharp blows. To increase the wearing qualities of the plow still further a patch of very hard cast steel is welded over the point of the share. Thus both conflicting requirements of softness and extreme hardness are met.