RATIONALE OF DRAININO LAND EXPLAINED. 



oacy of their roots. In short, in ordinary culture, to prevent these jihiuts from 

 bcinir too stronji:ly heated, or too qnickly dried by the heat of the sun, water is 

 frc(inently given fully on the sides, and thus they are in great danger of suffering 

 by excess of dampness. — Flore de Serres. 



RATIONALE OF DRAINING LAND EXPLAINED. 



The reason why drained land frains heat, and water-lojrged land is always cold, 

 consists in the well-known fact that heat cannot be transmitted downivards through 

 water. This may readily be seen by the following experiments : — 



Experiment No. 1. — A square box W'as 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^° 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, h, dipjjing 

 under the surface of the water at e, was then intro- 

 duced, 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 " . . . . 80i° 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°. 



Exferiment 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 ther- 

 mometer, 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 elfected, and, at the end of twenty 

 minutes, the thermometer, o, indicated 40° ; at twenty-five minutes, 42°, whilst 

 the thermometer, h, 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, h, indicated 48°. The 

 mass was drained and permeable to a fresh sui)ply of water. Accordingly, another 

 gallon of boiling water was poured over it, and, in 



3 minutes, the thermometer, o, rose to 77°. 



5 " " « fell to 76^°. 



15 " " « " 70^- 



20 " " « remained at 71^ 



1 hour 50 " " " " " 70^' 



