1884.] Himalaya Snowfall with Drought in India. 19 



dddu of Hnrdwar, are local and exceptional phenomena, restricted to 

 certain hours of the day. At all the hill stations of the outer North- 

 West Himalaya, as far as the existing registers show, southerly winds 

 preponderate over northerly, all through the year ; and although this 

 is probably due in some measure to the fact that the night winds 

 have not hitherto been registered, it suffices to show that up to a 

 level of 7,000 feet there is no steady outflow of air from the hills to 

 the plains. 



There remains then only the supposition that these winds are fed 

 by the descent of air from an upper stratum, viz., from a current 

 moving at a considerable elevation from west to east. And that this 

 is their true explanation several facts seem to testify. In the first 

 place, they are characteristically winds of the day time, their move- 

 ment being at a minimum (almost or quite a calm) in the morning 

 hours, and indeed up to 9 or 10 o'clock in the forenoon ; then 

 increasing with the temperature and falling again towards evening ; 

 and, secondly, such observations as have been made on the decrease 

 of temperature with elevation, show that, in the dry weather, the 

 vertical decrement is such as is incompatible with the vertical 

 equilibrium of an air column, being considerably more than 1 in 

 183 feet. The diurnal variation of the movement is then probably to 

 be accounted for on Koppen's hypothesis, viz., the interchange of the 

 higher and lower air strata by convective movements, which do not 

 affect the existing horizontal movement of the higher atmosphere, so 

 that the air of the latter, after its descent, preserves for a time its 

 original eastward motion. The hypothesis of convective interchange 

 receives further support from the character of the diurnal variation 

 curve of vapour tension in a dry atmosphere near the earth's 

 surface, which is the same in all parts of India. This shows a rapid 

 'fall of the absolute humidity of the air after 8 or 9 o'clock in the 

 forenoon, reaching its minimum about the time of greatest heat, and 

 a more or less sudden rise before sunset which it is difficult to 

 account for on any other supposition than that it coincides with the 

 cessation of the convective movement.* 



Systematic observations on the movement of the clouds, and more 

 especially the higher clouds in the upper provinces during the dry 

 season, are unfortunately as yet wanting, but according to such 

 casual observations as I have myself made when on inspection tours 

 in the cold season and during the spring months or hot season at 

 Simla, go to show that the movement is generally, if not always, 

 from some westerly quarter, and most frequently from the north- 

 west. 



* See, for instance, Plates II, Till, and XXVI of vol. i of these memoirs. The 

 curres of Yarkhand and Allahabad show that this type of variation is characteristic 

 the months in wliich the range of temperature is greatest. 



c2 



