which would be evaporated from drained land, would be equal to that gained by 11-1/3 tons of coal, which would cost $68; and this for each acre, in each of the three months. At whatever temperature a liquid vaporizes, it absorbs the same total quantity of heat. The latent heat of watery vapor at 212 deg. is 972 deg.; that is, when water at 212 deg. is converted into vapor at the same temperature, the amount of heat expended in the process is 972 deg.. This heat becomes latent, or insensible to the thermometer. The heat rendered latent by converting ice into water is about 140 deg.. There are 7.4805 gallons in a cubic foot of water which weighs 62.38 lbs." We have seen that a sea of water, more than three feet deep over the whole face of the land, falls annually from the clouds, equal to 4,000 tons in weight to every acre. We would use enough of this water to dissolve the elements of fertility in the soil, and fit them for the food of plants. We would retain it all in our fields, long enough to take from it its stores of fertilizing substances, brought from reeking marshes and steaming cities on cloud-wings to our farms. We would, after taking enough of its moisture to cool the parched earth, and to fit the soil for germination and vegetable growth, discharge the surplus, which must otherwise stagnate in the subsoil, by rapid drainage into the natural streams and rivers. Evaporation proceeds more rapidly from a surface of water, than from a surface of land, unless it be a saturated surface. It proceeds more rapidly in the sun than in the shade, and it proceeds again more rapidly in warm than in cold weather. It varies much with the culture of the field, whether in grass, or tillage, or fallow, and with its condition, as to being dry or wet, and with its formation, whether level or hilly. Yet, with all these variations, very great reliance may be placed upon the ascertained results of the observations already at our command. We have seen that evaporation from a water surface is, in general, greater than from land, and here we may observe one of those grand compensating designs of Providence which exist through all nature. If the same quantity of water fell upon the sea and the land, and the evaporation were the same from both, then all the rivers running into the sea would soon convey to it all the water, and the sea would be full. But though nearly as much water falls on the sea as on the land, yet evaporation is much greater from the water than from land. About three feet of rain falls upon the _water_, while the evaporation from a water surface far exceeds that amount. In the neighborhood of Boston, evaporation from water surface is said to be 56 inches in the year, and in the State of New York, about 50 inches; while, in England, it is put by Mr. Dalton at 44.43 inches, and, by others, much lower.