500 



FREQUENCY OF OCCURRENCES AT BHI 

 Four Hour Intervals 



2000 



28 FEB. 61 

 24 Hours 



2000 



6 MAR. 61 

 24 Hours 



2000 2000 



7 MAR. 61 13 MAR. 61 



24 Hours 24 Hours 



TIME 



2000 2000 



18 MAR. 6! 19 MAR. 61 

 24 Hours 24 Hours 



FIG. 17 



