PART I.] 



Relation of Rainfall to Cholera-prevalence. 



223 



with a fall ranging from 1*28 in March to 5-46 in May. Next follows a second period 

 of four months — that of the rainy season — with averages ranging from 10 to nearly 



Average Rainfall = \1 years [Inverted 

 curve]. 



Total monthly Cholera Deaths [88 

 years J. 



^BSSBBSSBBBBBB 



SEBaaBa aaaBBBB 



— 0"-0 Rainfall. 

 — 5"-0 „ 



-13" -7 ,. 



PlAGRAM 5. — Rainfall and Cholera-prevalence in Calcutta. (The Engraver has not kept 

 the curve rigidly to the scale in some parts.) 



14 inches, and finally we have October with an average of 5'61 inches, which is almost 

 identical with that of May. Stated generally, there are four months of maximum, 

 four months of minimum, and four months of intermediate rainfall ; but whilst the 

 months of maximum and minimum form continuous groups, the intermediate months 

 are divided into two unequal sections by the other periods, three of them intervening 

 between the minimum and maximum, and the fourth between the maximum and 

 minimum periods. 



On comparing the seasonal rhythm of cholera-prevalence with that of rainfall, 

 we find that the months for the former also fall into three groups of maximum, 

 minimum and intermediate prevalence. The groups in this case, however, do not 

 precisely correspond with those of rainfall, for whilst that of maximum includes four 

 months, that of minimum includes three only, and the remaining five months form 

 the intermediate group. 



Table XXV shows the relation which the three groups of months, arranged 

 in reference to rainfall and prevalence, bear to one another. 



The minimum months of prevalence correspond with three of maximum rainfall ; 

 the maximum months of prevalence coincide with one of minimum and three of 

 intermediate rainfall ; the intermediate months of prevalence coincide with three of 

 minimum, one of intermediate, and one of maximum rainfall. The correspondence 

 between special phenomena of prevalence and special periods of rainfall is much 

 less distinct than that between the phenomena of atmospheric humidity and of 

 prevalence. Beyond the fact that the three months of minimum prevalence correspond 

 with three of the period of maximum rainfall, there is nothing indicating any special 

 relation either direct or inverse between the two phenomena. 



