80 H. F. Blanford — On the relations of cloud [No. 2, 



In general, and with but few and temporary exceptions, the pressure 

 of the whole of India, was, throughout the year 1879, as persistently below 

 the average, as it had been above it during the two years ending with 

 August 1878 ; the depression, which set in in September 1878, having been 

 almost continuous up to, at least, the end of 1879. As in the case of the 

 preceding and opposite anomaly, this condition was evidently not due to 

 the reduced density of the lower atmosphere, except partially in the months 

 of April and May. For, the density of the lowest stratum, and therefore 

 its static pressure, was above the average in March, and, in most cases, 

 from June to the end of the year ; on the mean of the whole year, the 

 pressure of this stratum was in excess ; as might have been expected from 

 the fact, that its mean temperature was below the average ; but this excess 

 was more than neutralised by the deficiency of pressure of the higher strata, 

 and the total pressure was in defect in all months, excepting July and 

 partially in March, June, September, and November, Thus, then, we 

 have, in 1879, conditions precisely the reverse of those obtaining in 1877 

 and the earlier part of 1878, when the temperature of the lower stratum 

 being excessive, was accompanied by a density less than the average ; but 

 this anomaly was neutralised and outbalanced by the excessive pressure of 

 the elevated strata. 



Is this contrast of conditions in the lower and higher atmospheric 

 strata, thus doubly illustrated in the barometric features of the last three 

 or four years, a law of general incidence ? and is it traceable to the play of 

 physical processes which accompany these abnormal conditions ? There are 

 many circumstances which lead me to think this probable. 



I must premise that- the opposition of conditions, the coincidence of a 

 decrease in the density of the higher with an increase in that of the lower 

 strata of the atmosphere, and vice versa, so far from being an extraordinary 

 feature of our atmosphere, is one of regular annual occurrence in India. 

 In Central India, May, in the North -Western Provinces either May or 

 June, (according as the rains begin early or late), is the hottest month in 

 the year. The first fall of rain brings about a rapid fall of temperature 

 and with it a corresponding increase in the density of the lower air 

 stratum ; but notwithstanding this increase of density, there is no corre- 

 sponding increase in the total pressure of the atmosphere. On the contrary, 

 the minimum pressure does not occur until some weeks later ; and, at the 

 hill-stations, from 4,500 to 7,000 feet, above the plains, the pressure of the 

 atmosphere continues falling till July. Hence, it must be concluded that 

 the setting- in of the rains is accompanied by a decrease in the static pres- 

 sure of the higher strata, which compensates, or more than compensates, 

 the increased density of the lower. The following data serve to illustrate 

 this :— 



