WARMTH CAUSED BY DRAINAGE. 137 



ground at Chiswick is only 1°13 as is shown at p. 125, while 

 that of Trevandrum, an Indian station, is 5°69. But it must be 

 remembered that, disregarding means, the monthly temperature 

 exhibits very much greater differences. Thus at Chiswick 

 the earth is nearly 4° warmer than the air in December, and 

 that of Trevandrum is nearly 6^° warmer in the month of 

 February : these differences are themselves insignificant when 

 contrasted with what occurs at Upsal (p. 119), where the earth 

 is warmer than the air by 13°37 in the month of February. It 

 seems evident that in the examples of a high winter tempera- 

 ture of the earth in severe latitudes, we have an example of the 

 protection thus afforded to the vitality of plants iu the manner 

 suggested in the preceding page. 



There can be no sort of doubt, that the advantage derived from 

 draining cold countries, is owing greatly, if not exclusively, to the 

 augmented temperature which attends the removal of stagnant water 

 from land. Undergeound Cximatb is not less important than that^ 

 which is experienced above ground. It is only by perfect and skilful 

 drainage that underground climate is improved. No other means of 

 effecting it on a large scale are known ; it is probable indeed that the 

 superiority of common littery stable manure over artificial composts, as 

 weU. as the increased efficacy of the latter when mixed with the former, 

 is a mere exempUflcation of the advantageous effects of perfect 

 drainage. 



Some believe that the advantage of drainage consists in removing 

 water. But water is not of itself an evil ; on the contrary it is the 

 food of plants, and its absence is attended with fatal results. It is the 

 excess of water which injures plants, just as an excess of food injures 

 animals. Those who imagine that the advantage of drainage arises from 

 the removal of stagnant water, or any such cause alone, overlook the great 

 and important fact that drained land is, in summer, from 10° to 20° 

 warmer than water-logged land. Professor Schubler long ago came to 

 the conclusion that the loss of heat caused by evaporation in undrained 

 lands amounted to 11J° to 13|° Fahr. Mr. Parkes has shown, in his 

 " Essay on the Philosophy of Drainage," that in draining the Red Moss 

 near Bolton-le-Moors, the thermometer in the drained land rose in 

 June, 1837, to 66° at seven inches below the surface, while in the 

 neighbouring water-logged land it woiild never rise above 47°, an 

 enormous gain. In the garden of the Horticultural Society the mean 

 temperature of the thoroughly drained soil at one foot below the surface 

 is, in the month of July, 63°49 ; if we take that of water-logged land 

 to be the same as spring water, or 47°, there is a gain of 16^°. Thus it 



