"Experiment No. 2.—With the same arrangement as in the preceding case, a gallon of boiling water was introduced above the peat and water, when the thermometer a, was at 36°; in ten minutes it rose to 40°. The cock was then turned for the purpose of drainage, which was but slowly effected; and, at the end of twenty minutes, the thermometer a, indicated 40°; at twenty-five minutes, 42°, whilst the thermometer b, was 142°. At thirty minutes, the cock was withdrawn from the box, and more free egress of water being thus afforded, at thirty-five minutes the flow was no longer continuous, and the thermometer b, indicated 48°. The mass was drained, and permeable to a fresh supply of water. Accordingly, another gallon of boiling water was poured over it; and, in
| 3 | minutes, the thermometer a, rose to | 77°. |
| 5 | minutes, the thermometer a, fell to | 76½°. |
| 15 | minutes, the thermometer a, fell to | 70½°. |
| 20 | minutes, the thermometer a, remained at | 71°. |
| 1 hour 50 | minutes, the thermometer a, remained at | 70½°. |
"In these two experiments, the thermometer at the bottom of the box suddenly rose a few degrees immediately after the hot water was added; and it might be inferred that the heat was carried downwards by the water. But, in reality, the rise was owing to the action of the hot water on the thermometer, and not to its action upon the cold water. To prove this, the perpendicular thermometers were removed. The box was filled with peat and water to within three inches of the top, a horizontal thermometer, a f, having been previously secured through a hole made in the side of the box, by means of a tight-fitting cork, in which the naked stem of the thermometer was grooved. A gallon of boiling water was then added. The thermometer, a very delicate one, was not in the least affected by the boiling water in the top of the box.
"In this experiment, the wooden box may be supposed to be a field; the peat and cold water represent the water-logged portion; rain falls on the surface, and becomes warmed by contact with the soil, and, thus heated, descends. But it is stopped by the cold water, and the heat will go no further. But, if the soil is drained, and not water-logged, the warm rain trickles through the crevices of the earth, carrying to the drain-level the high temperature it had gained on the surface, parts with it to the soil as it passes down, and thus produces that bottom heat which is so essential to plants, although so few suspect its existence."
Water, although it will not conduct heat downwards, is a ready vehicle of cold from the surface towards the bottom. Water becomes heavier by cooling till it is reduced to about 39°, at which point it attains its greatest density, and has a tendency to go to the bottom until the whole mass is reduced to this low temperature. Thus, the circulation of water in the saturated soil, in some conditions of the temperature of the surface and subsoil, may have a chilling effect which could not be produced on drained soil.
After water is reduced to about 39°, instead of obeying the common law of becoming heavier by cooling, it forms a remarkable exception to it, and becomes lighter until it freezes. Were it not for this admirable provision of Nature, all our ponds and rivers would, in the Winter, become solid ice from the surface to the bottom. Now as the surface water is chilled it goes to the bottom, and is replaced by warmer water, which rises, until the whole is reduced to the point of greatest density. Then the circulation ceases, and the water colder than 39° remains at the surface, is converted into ice which becomes still lighter, by crystallization, and floats upon the surface.
No experiments, showing the temperature of undrained soils at various depths, in the United States, have come to our knowledge. Mr. Gisborne says: "Many experiments have shown that, in retentive soils, the temperature, at two or three feet below the surface of the water-table, is, at no period of the year, higher than from 46° to 48° in agricultural Britain." Prof. Henry states in the Patent Office Report for 1857, that in the cellars of the observatory, at Paris, at the depth of sixty-seven and a half feet, in fifty years, the temperature has never varied a tenth of a degree from 53° 28', in all that period, Summer or Winter.
Mr. Parkes gives the results of a valuable series of experiments, in which he compared the temperature of drained and undrained portions of a bog. He found the temperature of the undrained portion to remain steadily at 46°, at all depths, from one to thirty feet; and at seven inches from the surface, the temperature remained at 47° during the experiments. During the same period, the temperature of the drained portion was 48¼° at two feet seven inches below the surface, and at seven inches, reached as high as 66° during a thunder-storm; while, on a mean of thirty-five observations, the temperature at the latter depth was 10° higher than at the same depth in the undrained portion of the bog.
We find in the "Agriculture of New York," the results of observations made at Albany and at Scott, in that State, in the year 1848, upon temperature at different depths. The condition of the soil is not described, but it is presumed that it was soil naturally drained in both cases. A few of the results may give the reader some idea of the range of underground temperature, as compared with that of the air.
| Temperature | at | Albany | at two feet depth. | |
| " | " | " | highest August 17 and 18, | 70° |
| " | " | " | lowest February 28, | 32¾° |
| " | " | " | Range, | 37¼° |
| " | " | " | at four feet depth. | |
| " | " | " | highest July 29, | 64½° |
| " | " | " | lowest February 25, | 35½° |
| " | " | " | Range, | 29° |
| " | " | " | of the air, February 12, | -3° |
| " | " | " | of the air, August, 3, P. M., | 90° |
| " | " | " | Range, | 93° |
| Temperature | at | Scott | at two feet depth. | |
| " | " | " | highest, August 17 and 18, | 64° |
| " | " | " | at four ft. depth, 17 days in Aug. | 60° |
| " | " | " | of the air, at 3, P. M., highest | 90° |