[AK] It is probable that a composition of hydraulic cement and some soluble material will be invented, by which a continuous pipe may be laid in the bottoms of trenches, becoming porous as the soluble material is removed by water. CHAPTER III. ADVANTAGES OF UNDER-DRAINING. The advantages of under-draining are many and important. 1. It entirely prevents drought. 2. It furnishes an increased supply of atmospheric fertilizers. 3. It warms the lower portions of the soil. 4. It hastens the decomposition of roots and other organic matter. 5. It accelerates the disintegration of the mineral matters in the soil. 6. It causes a more even distribution of nutritious matters among those parts of soil traversed by roots. 7. It improves the mechanical texture of the soil. 8. It causes the poisonous excrementitious matter of plants to be carried out of the reach of their roots. 9. It prevents grasses from running out. 10. It enables us to deepen the surface soil. By removing excess of water-- 11. It renders soils earlier in the spring. 12. It prevents the throwing out of grain in winter. 13. It allows us to work sooner after rains. 14. It keeps off the effects of cold weather longer in the fall. 15. It prevents the formation of _acetic_ and other organic acids, which induce the growth of sorrel and similar weeds. 16. It hastens the decay of vegetable matter, and the finer comminution of the earthy parts of the soil. 17. It prevents, in a great measure, the evaporation of water, and the consequent abstraction of heat from the soil. 18. It admits fresh quantities of water from rains, etc., which are always more or less imbued with the fertilizing gases of the atmosphere, to be deposited among the absorbent parts of soil, and given up to the necessities of plants. 19. It prevents the formation of so hard a crust on the surface of the soil as is customary on heavy lands. * * * * * [How does under-draining prevent drought?] 1. Under-draining _prevents drought_, because it gives a better circulation of air in the soil; (it does so by making it more open). There is always the same amount of water _in_ and _about_ the surface of the earth. In winter, there is more in the soil than in summer, while in summer, that which has been dried out of the soil exists in the atmosphere in the form of a _vapor_. It is held in the vapory form by _heat_, which acts as _braces_ to keep it distended. When vapor comes in contact with substances sufficiently colder than itself, it gives up its heat--thus losing its braces--contracts, and becomes liquid water. This may be observed in hundreds of common operations. [Why is there less water in the soil in summer than in winter, and where does it exist? What holds it in its vapory form? How is it affected by cold substances? Describe the deposit of moisture on the outside of a pitcher in summer. What other instances of the same action can be named?]