PART I.] Monthly Averages of Water-level and Rainfall in Calcutta. 229 



The entire period has been sub-divided from November to November, both to render 

 the diagram uniform with those of the general averages, and also because November really 

 forms a more natural beginning of the year in respect to cholera in Calcutta than January 

 does. The prevalence during each annual period has been calculated from the figures in 

 Dr. Payne's table. 



The only point in the diagram deserving special notice here is, that it shows that the 

 two years of the period which were distinguished by minimum prevalence of cholera, 1871 

 and 1872, were both years in which there was relatively slight depression of the water- 

 level, succeeding seasons in which there had been excessive elevation of it. The 

 minimum of depression and the maximum of elevation both occurred in 1871 : the 



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Diagram 7. — The mouthly fluctuatiuud iii Watur-level and L'holera-prevaleticc iu Calcutta, together with 

 the mean monthly Rainfall, since 1870. [The water-level and rainfall-curves inverted.] 



minimum succeeded a season in which the elevation was the third highest for the period : 

 the maximum preceded one in which the depression was the third smallest. Further 

 than this, however, no special coincidence can be traced between the phenomena of water- 

 level and prevalence ; but the fact that the season of 1873-74 was one of low prevalence 

 for the period again shows that mere depression of water-level, mere diminution of the 

 bulk of water in the soil, is insufficient, in itself, to secure prevalence. 



One result of the observations has been to show that the water-level in Calcutta 

 cannot be accurately estimated from the data of rainfall alone, and more especially from 

 those of total annual rainfall. The distribution of the rain throughout the year must 



