18G J. Eliot — The South-West Monsoon Storms of the Bay of Bengal. 



EXPLANATION OF PLATES II— X. 



The plates give the weather charts for each day during the whole period 

 covered by the two storms of 1883 described in the preceding pages. The curved 

 lines or isobars indicate the distribution of pressure. Along any one of these lines, 

 the estimated air pressure at the sea-level (as determined from the reading of the 

 barometer) is the same. Hence no change of pressure occurs along these lines, and 

 the change of pressure is greatest perpendicularly across these lines. The rate of 

 change is most rapid where the lines are nearest together. As the difEerence of air 

 pressure between consecutive lines is the same, the rate of increase or decrease of 

 pressure is inversely proportional to the distance between consecutive lines. The 

 isobars form closed curves about the centre of a cyclonic disturbance. Hence the 

 position of the cyclonic vortex on any day is at once determined by an inspection of 

 the charts. The probable path is determined by joining these positions by lines . 

 The direction of the air motion near the earth's surface is determined by the winds, 

 which are shown by arrows flying with the wind, or pointing to the direction 

 towards which the moving air is advancing. Small circles ( o ) indicate a calm at 

 the hour of observation. 



The charts give the distribution of pressure and wind directions at 10 A. M. of 

 each day. They are based on the 10 a. m. observations taken at the land meteoro- 

 logical stations, and on the 8 A. m. or noon observations taken on board the ships 

 which have furnished logs of the weather experienced by them in the Bay during 

 either storm, allowance being made, wherever at is possible, for the difference of time 

 between the two sets of observations. 



