Drainage raises the temperature of the soil, by allowing the rain to pass downwards. In the growing season, especially in the Spring, the rain is considerably warmer than the soil. If the soil be saturated with the cold snow-water, the water which falls must, of course, run away upon the surface. If the soil be drained, the rain-water finds ready admission into it, carrying and imparting to it a portion of its heat. The experiments of Count Rumford, showing that heat is not propagated downward in fluids, may be found at page [273]. This is a principle too important to be overlooked, especially in New England, where we need every aid from Nature and Art, to contend successfully against the brevity of the planting season. Soil saturated with cold water, cannot be warmed by any amount of heat applied to the surface. Warm water is lighter than cold water, and stays at the surface. In boiling water in a kettle, we apply fire at the bottom, and no amount of heat at the surface of the vessel would produce the desired effect. So rapid is the passage of heat upward in water, that the hand may without injury be held upon the bottom of a kettle of boiling water one minute after it has been removed from the fire.
The following experiments and illustrations, from the Horticulturist of Nov. 1856, beautifully illustrate this point:
"RATIONALE OF DRAINING LAND EXPLAINED.
"The reason why drained land gains heat, and water-logged land is always cold, consists in the well-known fact that heat cannot be transmitted downwards through water. This may readily be seen by the following experiments:
Fig. 97.
"Experiment No. 1.—A square box was made, of the form represented by the annexed diagram, eighteen inches deep, eleven inches wide at top, and six inches wide at bottom. It was filled with peat, saturated with water to c, forming to that depth (twelve and a half inches) a sort of artificial bog. The box was then filled with water to d. A thermometer a, was plunged, so that its bulb was within one inch and a half of the bottom. The temperature of the whole mass of peat and water was found to be 39½° Fahr. A gallon of boiling water was then added; it raised the surface of the water to e. In five minutes, the thermometer, a, rose to 44°, owing to the conduction of heat by the thermometer and its guard tube; at ten minutes from the introduction of the hot water, the thermometer, a, rose to 46°, and it subsequently rose no higher. Another thermometer, b, dipping under the surface of the water at e, was then introduced, and the following are the indications of the two thermometers at the respective intervals, reckoning from the time the hot water was supplied:
| Thermometer b. | Thermometer a. | ||||
|---|---|---|---|---|---|
| 20 | minutes | 150° | 46° | ||
| 1 | hour | 30 | " | 101° | 45° |
| 2 | hours | 30 | " | 80½° | 42° |
| 12 | " | 40 | " | 45° | 40° |
"The mean temperature of the external air to which the box was exposed during the above period, was 42°, the maximum being 47°, and the minimum 37°.