The horse-shoe tiles, we understand, have been generally used in New York. At Albany, and in Massachusetts, the sole-tile has been of late years preferred. We cannot learn that cylindrical pipes have ever been manufactured in this country until the Summer of 1858 when the engineers of the New York Central Park procured them to be made, and laid them, with collars, in their drainage-works there. This is believed to be the first practical introduction into this country of round pipes and collars, which are regarded in England as the most perfect means of drainage. Experiments all over the country, in reclaiming bog-meadows, and in draining wet lands with drains of stone and wood, have been attempted, with various success. Those attempts we regard as merely efforts in the right direction, and rather as evidence of a general conviction of the want, by the American farmer, of a cheap and efficient mode of drainage, than as an introduction of a system of thorough drainage; for--as we think will appear in the course of this work--no system of drainage can be made sufficiently cheap and efficient for general adoption, with other materials than drain-tiles. CHAPTER III. RAIN, EVAPORATION, AND FILTRATION. Fertilizing Substances in Rain Water.--Amount of Rain Fall in United States--in England.--Tables of Rain Fall.--Number of Rainy Days, and Quantity of Rain each Month.--Snow, how Computed as Water.--Proportion of Rain Evaporated.--What Quantity of Water Dry Soil will Hold.--Dew Point.--How Evaporation Cools Bodies.--Artificial Heat Underground.--Tables of Filtration and Evaporation. Although we usually regard drainage as a means of rendering land sufficiently dry for cultivation, that is by no means a comprehensive view of the objects of the operation. Rain is the principal source of moisture, and a surplus of moisture is the evil against which we contend in draining. But rain is also a principal source of fertility, not only because it affords the necessary moisture to dissolve the elements of fertility already in the soil, but also because it contains in itself, or brings with it from the atmosphere, valuable fertilizing substances. In a learned article by Mr. Caird, in the Cyclopedia of Agriculture, on the Rotation of Crops, he says: "The surprising effects of a fallow, even when unaided by any manure, has received some explanation by the recent discovery of Mr. Barral, that rain-water contains within itself, and conveys into the soil, fertilizing substances of the utmost importance, equivalent, in a fall of rain of 24 inches per annum, to the quantity of ammonia contained in 2 cwt. of Peruvian guano, with 150 lbs. of nitrogeneous matter besides, all suited to the nutrition of our crops."