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 deg., 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 deg., 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 deg.
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 deg. to 48 deg. in
agricultural Britain." Prof. Henry states in the Patent Office Report
for 1857, t