Appendix H. ON THE TEMPERATURE OF THE SOIL. 441 



becoming excessively heated, and the temperature being higher than 

 at Calcutta. This indeed follows from the well known fact that the 

 summer heat increases greatly in advancing north-west from the Bay 

 of Bengal to the trans- Sutledge regions ; it is admirably expressed in 

 the maps of Dove's great work " On the Distribution of Heat on the 

 Surface of the Globe." 



H. 

 ON THE TEMPEHATUEE OF THE SOIL AT VARIOUS ELEVATIONS. 



These observations were taken by burying a brass tube two feet 

 six inches to three feet deep, in exposed soil, and sinking in it, by 

 a string or tied to a slip of wood, a thermometer whose bulb was 

 well padded with wool : this, after a few hours' rest, indicates the 

 temperature of the soil. Such a tube and thermometer I usually 

 caused to be sunk wherever I halted, if even for one night, except 

 during the height of the rains, which are so heavy that they commu- 

 nicate to the earth a temperature considerably above that of the air. 



The results proved that the temperature of the soil at Dorjiling 

 varies with that of the month, from 46° to 622°, but is hardly 

 affected by the diurnal variation, except in extreme cases. In summer, 

 throughout the rains, May to October, the temperature is that of the 

 month, which is imparted by the rain to the depth of eleven feet 

 during heavy continued falls (of six to twelve inches a day), on which 

 occasions I have seen the buried thermometer indicating a tempera- 

 ture above the mean of the month. Again, in the winter months, 

 December and January, it stands 5° above the monthly mean ; in 

 November and February 4° to 5° ; in March a few degrees below the 

 mean temperature of the month, and in October above it ; April 

 and May being sunny, it stands above their mean ; June to 

 September a little below the mean temperature of each respectively. 



The temperature of the soil is affected by : — 1. The exposure of 

 the surface ; 2. The nature of the soil ; 3. Its permeability by rain, 

 and the presence of underground springs ; 4. The sun's declination ; 

 5. The elevation above the sea, and consequently the heating power 

 of the sun's rays : and, 6, The amount of cloud and sunshine. 



The appended observations, though taken at sixty-seven places, are 



