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 experiment: -

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 and a half inch of the bottom. The temperature of the whole mass of peat and water was found to be 39 1/2° 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:-

Experiment No 1 1100142

Thermometer 6.

Thermometer a.

20 minutes .

. 150°

46°.

1 hour 30 " . .

. 101° "

45°.

2 hours 30 "...

80 1/2o

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°.

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 46°; at twenty-five minutes, 42°, whilst the thermometer, 6, 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 At thirty minutes, the cock was withdrawn from the box, and more free egress of.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 oyer it, and, in.

8 minutes, the thermometer, a, rose to 77°.

6 " " " fell to 764°.

15 " " " " 7o 1/2o.

20 " " " remained at 71°.

1 hour 60 " " " " " 70 1/2o.

• 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 heat was carried downwards by the water. Bat, 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 stent of the thermometer was, grooved. A gallon of boiling water was then added. The thermometer, a very delicate one, was not 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 waterlogged 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 beat which is so essential to plants, although .so few suspect its existence.

This necessity of warmth at the root undoubtedly explains why it is that hardy trees, over whose roots earth has been heaped, or having laid, are found to suffer so much, or even to die; in such case, the earth in which the roots are growing is constantly much colder than the atmosphere, instead of wanner.

It is to the coldness of the earth that must be ascribed the common circumstance of vines that are forced early, not setting their fruit well when their roots are in the external border, and unprotected by artificial means; and to the same cause is often ascribed the thanking or shrivelling of grapes, which most commonly happens to vines whose roots are in a cold or unsunned border.