392 PHYSICAL GEOGRAPHY OF SIKKIM. Appendix E. 



broken into isolated peaks to drain the already nearly exhausted 

 current, whose condensed vapours roll along in fog beyond the 

 parallel of Kinchin, are dissipated during the day over the arid 

 mountains of Tibet, and deposited at night on the cooled surface of 

 the earth. 



Other phenomena of no less importance than the distribution of 

 vapour, and more or less depending on it, are the duration and 

 amount of solar and terrestrial radiation. Towards D the sun is 

 rarely seen during the rainy season, as well from the constant 

 presence of nimbi aloft, as from fog on the surface of the ground. 

 An absence of both light and heat is the result south of the parallel of 

 Kinchin ; and at C low fogs prevail at the same season, but do not 

 intercept either the same amount of light or heat ; whilst at T there 

 is much sunshine and bright light. During the night, again, there 

 is no terrestrial radiation between S and P ; the rain either continues 

 to pour — in some months with increased violence — or the saturated 

 atmosphere is condensed into a thick white mist, which hangs over 

 the redundant vegetation. A bright starlight night is almost 

 unknown in the summer months at 6000 to 10,000 feet, but is 

 frequent in December and January, and at intervals between 

 October and May, when, however, vegetation is little affected by 

 the cold of nocturnal radiation. In the regions north of Kinchin, 

 starlight nights are more frequent, and the cold produced by radia- 

 tion, at 14,000 feet, is often severe towards the end of the rains in 

 September. Still the amount of clear weather during the night is 

 small ; the fog clears off for an hour or two at sunset as the wind 

 falls, but the returning cold north current agaiu chills the air soon 

 afterwards, and rolling masses of vapour are hence flying overhead, 

 or sweeping the surface of the earth, throughout the summer nights. 

 In the Tibetan regions, on the other hand, bright nights and even 

 sharp frosts prevail throughout the warmest months. 



Referring again to the cut, it must be borne in mind that neither 

 of the two meridional ridges runs in a straight line, but that they 

 wind or zigzag as all mountain ranges do; that spurs from each 

 ridge are given off from either flank alternately, and that the origin 

 of a spur on one side answers to the source of a river (i.e., the head 

 of a valley) on the other. These rivers are feeders of the main 



