In England a very large sum from the public treasury has been appropriated as a fund for loans, on under-drains, which is lent to farmers for the purpose of under-draining their estates, the only security given being the increased value of the soil. The time allowed for payments is twenty years, and only five per cent. interest is charged. By the influence of this patronage, the actual wealth of the kingdom is being rapidly increased, while the farmers themselves, can raise their farms to any desired state of fertility, without immediate investment. [How does under-draining affect the healthfulness of marshy countries? Describe the sub-soil plow.] The best proof that the government has not acted injudiciously in this matter is, that private capitalists are fast employing their money in the same manner, and loans on under-drains are considered a very safe investment. There is no doubt that we may soon have similar facilities for improving our farms, and when we do, we shall find that it is unnecessary to move West to find good soil. The districts nearer market, where the expense of transportation is much less, may, by the aid of under-drains, and a judicious system of cultivation, be made equally fertile. One very important, though not strictly agricultural, effect of thorough drainage is its removal of certain local diseases, peculiar to the vicinity of marshy or low moist soils. The health-reports in several places in England, show that where _fever and ague_ was once common, it has almost entirely disappeared since the general use of under-drains in those localities. CHAPTER IV. SUB-SOIL PLOWING. [Describe the Mapes plow. Why is the motion in the soil of one and a half inches sufficient? How does the oxidation of the particles of the soil resemble the rusting of cannon balls in a pile?] The _sub-soil plow_ is an implement differing in figure from the surface plow. It does not turn a furrow, but merely runs through the subsoil like a mole--loosening and making it finer by lifting, but allowing it to fall back and occupy its former place. It usually follows the surface plow, entering the soil to the depth of from twelve to eighteen inches below the bottom of the surface furrow. The best pattern now made (the Mapes plow) is represented in the following figure. [Illustration: Fig. 8. The Mapes plow and its mode of action. _a_--Shape of the foot of the plow, _b_--Its effect on the soil.] The sub-soil plows first made raised the whole soil about eight inches, and required very great power in their use often six, eight, or even ten oxen. The Mapes plow, raising the soil but slightly, may be worked with much less power, and produces equally good results. It may be run to its full depth in most soils by a single yoke of oxen.