PART I.] Combined Influence of Temperature and Hum.idity. 



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in prevalence and rise in iiumidity occurs in May and June. The greatest want of 

 coincidence is presented by the phenomena of December and January and of April. 

 In December and January, as compared with November, there is diminished prevalence 

 coincident with diminished humidity, and in April compared with March, there is 

 increased humidity coincident with a prevalence which our data lead us to regard as 

 increased in place of diminished. 



The question of the influence of temperature may here be recurred to in reference 

 to the exceptional relations occupied by the humidity and prevalence of December and 

 January. Assuming that elevation of temperature and depression of humidity favour 

 the prevalence of cholera in Calcutta, and that the opposite conditions produce a 

 reverse effect, let us endeavour to estimate the combined effect of the conditions of 

 temperature and humidity present in each individual month. For convenience of 

 calculation, degrees of temperature and of humidity may be regarded as of equal value 

 in reference to prevalence. "We know that November is a month in which prevalence 

 is of nearly average intensity, and the conditions of the month which favour prevalence 

 must therefore occiipy a similar position in respect to those of other months. The 

 humidity of November is 71, its temperature is 74°*9. Passing to December, we have 

 a humidity of 68 and a temperature of 68°* 1 ; that is, we have increased prevalence 

 favoured by 3 degrees of humidity, and diminished prevalence favoured by 6'8 degrees 

 of temperature. According to this there is an excess of 3°'8 in favour of diminished 

 prevalence, and the conditions of December in respect of temperature and humidity 

 in relation to prevalence are as — 3°"8, compared with those of November as zero. 



Proceeding in the same way with the remaining months, we obtain the following 

 series of figures : — 



TABLE XXIII. 



Relatians of tJie various months in respect of combined influence of Humidity 



and Tem'perature. 



The relation borne by the combined conditions of temperature and humidity to 

 cholera prevalence is shown in Diagram 4 of the phenomena for the twelve-year period. 



It certainly is curious how closely the line representing the aggregate of conditions 

 here assumed to influence the prevalence of cholera corresponds with that representing 

 the actual prevalence. 



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