OCT — mar. 1858-59.] Progress of the Magnetic Survey. 337 



mometer, the bulb of which was made extremely insensible. The 

 observations of the temperature of the ground at Umerkuntuk, 

 compared with similar data around the base of the hill, afford 

 some curious examples of the cooling influences which extensive 

 jungles have upon the temperatue of the ground. At Umerkun- 

 tuk the temperature was, 22nd to 25th January. 



At one metre below the surface. . . .21° 2' Centigrade. 



„ two metres, „ 21° 5 „ 



At Paindra, more than 1,000 feet lower than Umerkuntuk, the 

 temperature was, 27th to 29th of January — 



Atone metre below the surface .... 20° 0' Centigrade. 



„ two metres, „ „ 21° 0' „ 



I observed similar differences at Ramgurh, and at some other 

 stations West and North of Umerkuntuk, which are all 1,000 

 to 1,300 feet lower than the plateau. 



This anomalous phenomenon seems to be due to the following 

 causes. 



The plateau of Umerkuntuk itself has comparatively little jun- 

 gle, and the ground is exposed freely to the action of the sun. 

 Round the base of Umerkuntuk, and especially on the slops of the 

 hills, very thick and extensive jungles prevail, which keep the 

 ground moist and cool, as they prevent the heating of the surface 

 by the powerful tropical sun. 



The meteorological observations which I had occasion to make 



in many parts of the jungles of Central 

 Influence of iungle on T ■,, „ , TT 



the temperature of the India > as wel1 as those of m ? Mother Her- 

 ground. mann in Assam, and of my brother Adolphe 



in the Godavery jungles, offer many strik- 

 ing examples of the cooling influence which extensive jungles 

 exercise in India on the temperature of the ground, as well as on 

 the. atmosphere. 



The anomalous cooling of the ground by jungles is still more 

 apparent than the difference of temperature in the air of jungles 

 when compared with open Districts, since the differences in the 

 temperature of the air are much more equalized by winds and at- 

 mospheric currents. 



