

1870.] Irregularities of Atmospheric pressure in Bengal, $•<?. 133 



Explanation of the Charts, PI. VIII. 

 The Charts shew the mean isobarie lines, the resultant wind 

 directions and distribution of that rainfall for each of the three 

 months, June and August, 1868, and June, 1869. The two former 

 data are obtained from registers kept at the stations : 



Koorki 



Monghyr 



Dacca 



False Point 



Benares 



Darjiling 



Jessore 



Madras 



Patna 



Berhampore 



Calcutta 



Chittagong 



Gya 



Goalpara 



Saugor Id. 



Akyab 



Hazaribaugh 



Shillong 



Cuttack 



Port Blair 



in the case of the Charts for June 1869. A few of these are want- 

 ing in the charts of the previous year. The rainfall data are ob- 

 tained from a larger number of Stations. 



The isobarie lines are obtained by reducing to sea level the means 

 of (in most cases) four observations daily, reduced for temperature 

 and corrected to the Calcutta standard. The lines represent differ- 

 ences of Y^ of an inch. To determine their position, the distances 

 between each pair of neighbouring stations, lying on opposite sides 

 of a line, were divided into parts proportional to the excess or defect 

 of their mean readings on the even tenth, and the line was drawn 

 through the series of points so determined. If the stations are 

 very distant, or the exact course of the line for other reasons doubtful, 

 it is represented by a broken line. 



The wind resultants are represented by arrows, the points of 

 which indicate the position of the stations to which they belong. 

 The direction of their flight indicates the mean motion of the wind, 

 as deduced from the number of observations, and without regard 

 to differences of velocity. The relative predominance of the resul- 

 tant direction is indicated by the length of the arrow, taking f inch 

 as the maximum or as representing exclusive prevalence. 



The distribution of rainfall is indicated by light dotted lines, 

 each line corresponding to a difference of 10 inches of fall during 

 the month. 



18 



