232 



Cholera in Relation to Certain Physical Phenomena. [part i. 



of the layer of soil, which lies permanently above the soil-water. The mean temperature 

 for the year is 78-5.* The minimum soil-temperature occurs in January ; the maximum 

 in June and July. The temperature exceeds that of the atmospheric air in the months 

 of November, December, and January; falls far short of it during March, April, and 

 May ; and is almost equal to it during the remaining months. These facts will receive 

 notice again ; but in the meantime it may be pointed out that, in so far as conditions 

 of temperature are concerned, soil-ventilation is favoured during November, December 

 and January ; obstructed during March, April and May ; and almost in equilibrium 

 during the remaining months. 



Comparing the data of soil-temperature and cholera-prevalence, we find that the 

 great maximum of prevalence in April and the minor elevation in November both 

 occur when the soil-temperature is between 78° and 79°, the actual figures being 78°-8 

 and 78°-], or at a mean elevation. Here, however, the coincidence ceases; for the 

 increase of soil-temperature after April, and the decrease after November, are both 

 associated with decreased cholera-prevalence. Whether the fact really be of any 

 important significance or not, it is, at all events, worthy of note that such a coincidence 

 should be present in reference to these two months ; for in other respects they differ 

 from one another considerably. The only other condition in which they tend to agree 

 is the atmospheric humidity : the atmospheric temperature, rainfall and water-level all 

 present important divergencies. The period of minimum prevalence occurs along with 

 that of maximum elevation of temperature ; but the same elevation extends beyond 

 it in both directions, commencing and terminating in June and October, two months 



* It may be of interest to compare the figures illustrating the relations of telluric and atmospheric tem- 

 perature in Calcutta with those of a locality where the temperature is very different. The following table 

 shows the mean temperature of the air and of the soil at a depth of 30-2 metres in St. Petersburg for each 

 month of 187'> (^Annalen des PhysilialiscJicn Central Obscrvatoriuvis — Jahrgang, 1875) : — 



TABLE XXXV («). 

 Mean Monthly Temperature of Air and SoU of St. Petersburg. 



