138 DRAINING SOIL WARMS IT. 



is eyident that drainage produces tie very important effect upon land of 

 raising its temperature ; it communicates bottom heat, in the absence of 

 some amount of which, even the common Nettle and Groundsel would 

 perish ; and as scarcely any of our cultivated crops are natives of 

 countries so cold as our own, it is manifest that they aU req[uire to have 

 the earth warmed for them, or are much the better for it. 



The reason why drained land gains heat, and water-logged land is 

 always cold, consists in the weU-known fact that heat cannot be 

 transmitted downwards through water. This may be readily seen by 

 the following experiments : — 



ExPBBiMEiirT Wo. I. — 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 



— -U- 



::::0 r.:. 



Fig. XXVII. 



with water to c, formiag, to that depth (twelve and a half inches), a 

 sort of aitittoial bog. The box was then fiUed with water to d. A 

 thermometer (o) 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 39i° Fahr. A gaUon of boiling water was 

 then added; it raised the surface of the water to c. In five minutes 

 the thermometer arose to 44°, owing to conduction of heat by the 

 thermometer tube, and its guard. At ten minutes from the introduction 

 of the hot water the thermometer a rose to 46°, and it subsequently 

 rose no higher. Another thermometer (6), dipping under the surface 

 of the water at e, was then introduced ; and the foUowing ore the indica- 

 tions of the two thermometers at the respective intervals, reckoning from 

 the time the hot water was supplied : 



