FART I.] Carbonic Acid of Soil-air in Relation to Cholera-prevalence. 233 



of medium prevalence. The fact, that a marked fall in the soil-temperature occurs 

 from November to the minimum in January, is of importance in connection with the 

 questions previously alluded to in the diminished prevalence during the same period. 

 We now see that if temperature really exert any influence, that of the soil must be 

 considered as well as that of the atmosphere above it ; and is even, perhaps, in this 

 case of more importance, as the course of the phenomena of soil-temperature in 

 December and January corresponds more closely with the course of the prevalence than 

 that of the atmospheric temperature does. 



(g) Carbonic acid of the Soil-air Soil-ventilation. 



TABLE XXXVI. 



C&niparison of the Tnoiithly average of Carbonic Acid [at 6 feet] tuith Gholera- 



po^evalence. 



The diagram, No. 9, on the following page, in this case is constructed from con- 

 fessedly very imperfect materials. Our data regarding the amount of carbonic acid in 

 the soil-air are as yet very limited, and those employed in the present instance are 

 derived from observations carried out for little more than a year — from July 1873 to 

 August 1874 — after which date the observations were unavoidably interrupted until 

 May 1877.* Certain facts have, however, been already ascertained regarding the course 

 of the fluctuations in amount of carbonic acid in the soil-air, so that the data of 1873-74 

 may be employed as illustrating the more general phenomena, although not constituting 

 rigid examples of the precise conditions actually present in individual years. 



* We are indebted to Mr. Henry F. Blanford, Meteorological Reporter to the Government of India, for 

 having made arrangements for the exposure of tubes charged with baryta solution at certain of the larger 

 Meteorological stations. The requisite apparatus has already been provided at Allahabad, Lucknow and Delhi, 

 and observations are now conducted at these places through the assistance of Mr. S. A. Hill, B.Sc, Dr. Bonavia 

 and Assistant- Surgeon Ra<^lha Kishen. The tubes charged with the baryta solution are sent by post to the 

 different stations at short intervals, returned after exposure, and the amount of carbonic acid determined. 



