1881.] and rainfall to temperature in India. 79 



In any discussion of the causes which affect the temperature and 

 modify the temperature anomaly of any given month or other short period, 

 there is one important circumstance which must not be overlooked, al- 

 though it is rarely referred to in the discussion of such questions. This 

 is the temperature of the ground. It seems to be established by the 

 observations of ground temperature, which have been made at Calcutta 

 during the last two years, that the ground, to a considerable depth, serves 

 as a reservoir of heat, the slow emission of which probably exercises an 

 appreciable influence on the temperature of the lowest air stratum ; and 

 this will be more especially the case in a region such as the Punjab, where 

 (in the cold season more particularly) the air has but little movement of 

 translation. This effect becomes apparent, when two or three months, in 

 succession, are characterised by abnormal dryness or its opposite, by the 

 gradual exaggeration of the temperature anomaly, whether positive or 

 negative, in the successive months. Of this phenomenon, examples have 

 been given in the table on a previous page, more especially in the case of 

 June, July, and August 1877, and March, April, and May 1879, in the 

 North- Western Provinces ; and many others may be noticed, in glancing 

 through the tables of temperature anomalies in the annual meteorological 

 reports. On the other hand, to the same modifying influence, may proba- 

 bly be traced in a large measure, the fact that homonymous months may 

 be very similarly characterised by unusual dryness or dampness in two differ- 

 ent years, and yet there may be a considerable difference in the temperature 

 anomaly, if the period of a month or two immediately preceding has been 

 of a different character in the two years compared. An instance of the 

 kind has occurred during the present year (1880), which will be duly 

 noticed in the annual report for that year. 



To sum up the principal conclusions arrived at in the foregoing dis- 

 cussion. At all times of the year, the air temperature is dependent, 1st, 

 on the quantity and intensity of the sunshine ; 2nd, on the terrestrial radi- 

 ation, which is predominantly active as a cooling action only at night ; and 

 3rd, on the evaporation of rain. The influence of cloud, which checks both 

 solar and terrestrial radiation, is such as, in conjunction with the rainfall, 

 (which varies more or less pari passu with it), to lower the temperature 

 from February to October, to raise it in November and December. On the 

 mean of the whole year, therefore, cloud and rain exercise a preponderating 

 cooling influence. The immediate effect of these agencies is, however, 

 much modified by the condition of the ground, which acts as a reservoir of 

 heat, and thus renders the temperature of any moderate period, to a certain 

 extent, dependent on the condition of the period preceding it. 



