442 ON THE TEMPERATURE OF THE SOIL. Appendix H. 



far from being sufficient to supply data for the exact estimation of 

 the effects of the sun on the soil at any elevation or locality ; they, 

 however, indicate with tolerable certainty the main features of this 

 phenomenon, and these are in entire conformity with more ample 

 series obtained elsewhere. The result, which at first sight appears 

 the most anomalous, is, that the mean temperature of the soil, at two 

 or three feet depth, is almost throughout the year in India above 

 that of the surrounding atmosphere. This has been also ascertained 

 to be the case in England by several observers, and the carefully- 

 conducted observations of Mr. Eobert Thompson at the Horticultural 

 Society's Gardens at Chiswick, show that the temperature of the 

 soil at that place is, on the mean of six years, at the depth of one 

 foot, 1° above that of the air, and at two feet 1^°. During the winter 

 months the soil is considerably (1° to 3°) warmer than the air, and 

 during summer the soil is a fraction of a degree cooler than the air. 



In India, the sun's declination being greater, these effects are much 

 exaggerated, the soil on the plains being in winter sometimes 9° hotter 

 than the air ; and at considerable elevations in the Himalaya very much 

 more than that ; in summer also, the temperature of the soil seldom 

 falls below that of the air, except where copious rain-falls communicate 

 a low temperature, or where forests interfere with the sun's rays. 



At considerable elevations these effects are so greatly increased, 

 that it is extremely probable that at certain localities the mean tem- 

 perature of the soil may be even 10° warmer than that of the air ; 

 thus, at Jongri, elevation 13,194 feet, the soil in January was 34*5°, 

 or 19-2° above the mean temperakire of the month, immediately 

 before the ground became covered with snow for the remainder of 

 the winter ; during the three succeeding months, therefore, the tem- 

 perature of the soil probably does not fall below that of the snow, 

 whilst the mean temperature of the air in January may be 

 estimated at about 20°, February 22°, March 30°, and April 

 35°. If, again, we assume the temperature of the soil of 

 Jongri to be that of other Sikkim localities between 10,000 

 and 14,000 feet, we may assume the soil to be warmer by 10° in 

 July (see Tungu observations), by 8° or 9° in September (see 

 Yeumtong) •/ by 10° in October (see Tungu) ; and by 7° to 10° in 

 November (see Wallanchoon and Nanki). These temperatures, 



