14 Report on the Magnetic Survey. [No. 1. 



In the following resume I will try to collect, in the form of an 

 extract from our journals, some meteorological phenomena which 

 seemed to me particularly interesting, either in their more general 

 character or from peculiarities characteristic of the regions explored. 



Decrease and variation of the temperature of the air. 



Comparing the Sikkim Himalaya in general with the plains, it is 

 very manifest that the law of decrease of temperature for the annual 

 and monthly means, as particularly for the extremes of single days, 

 is a very different one from the plains to the range of mountains 

 not exceeding 6000 or 7000 feet, and not very distant from the 

 plains — and from these mountains to the higher parts of the central 

 Himalayas. In the first case the decrease is much more rapid than 

 in the second. 



The temperature also of the lower part of the hills in the neigh- 

 bourhood of the plains is frequently affected by the fog, which 

 rapidly ascends along the slopes, and does not change the tempera- 

 ture of the air confined between the vesicles of vapour at a rate 

 corresponding to the variation of their height. 



A similar difference in the laws of decrease of temperature is 

 also clearly observable in the Khosia hills, though on a smaller scale ; 

 their steep flanks facing the south, and the gentle elevations of the 

 ridges based on the plateaux succeeding in the interior, present a 

 configuration particularly adapted to show such modifications. In 

 Assam, we got a very valuable set of meteorological observations 

 communicated to us through the kindness of Col. Jenkins, which, 

 combined and reduced by our own observations, will allow us to 

 trace the thermic lines with great detail. 



The temperature of the ground, of rivers, and of springs, has been 

 always carefully observed. 



I add, as an interesting object for comparison with the preceding 

 tables, some numbers obtained in Gowhatty, Central Assam, the 

 instrument being employed on ground covered with short grass. 



