Feb. 1848. WINTER CLIMATE OF BEHAR. 15 



radiation of heat from the latter to the clear sky above. 

 Such strata may be observed, crossing the hills in ribbon- 

 like masses, though not so clearly on this elevated region 

 as on the plains bounding the lower course of the Soane, 

 where the vapour is more dense, the hills more scattered, 

 and the whole atmosphere more humid. During the ten 

 days I spent amongst the hills I saw but one cloudy sun- 

 rise, whereas below, whether at Calcutta, or on the banks of 

 the Soane, the sun always rose behind a dense fog-bank. 



At 9-Jr a.m. the black-bulb thermometer rose in the sun 

 to 130°. The morning observation before 10 or 11 a.m. 

 always gives a higher result than at noon, though the sun's 

 declination is so considerably less, and in the hottest part 

 of the day it is lower still (3-J- p. m. 109°), an effect no 

 doubt due to the vapours raised by the sun, and which 

 equally interfere with the photometer observations. The 

 N.W. winds invariably rise at about 9 a.m. and blow with 

 increasing strength till sunset ; they are due to the rare- 

 faction of the air over the heated ground, and being loaded 

 with dust, the temperature of the atmosphere is hence 

 raised by the heated particles. The increased temperature 

 of the afternoon is therefore not so much due to the 

 accumulation of caloric from the sun's rays, as to the 

 passage of a heated current of air derived from the much 

 hotter regions to the westward. It would be interesting 

 to know how far this N.W. diurnal tide extends ; also the 

 rate at which it gathers moisture in its progress over the 

 damp regions of the Sunderbunds. Its excessive dryness 

 in N.W. India approaches that of the African and 

 Australian deserts ; and I shall give an abstract of my own 

 observations, both in the vallies of the Soane and Ganges, 

 and on the elevated plateaus of Behar and of Mirzapore.* 



* See Appendix A. 



