28 



Lieut.-Col. Sabine on some Points in 

 Table I. 



Bombay, 1843. — Mean Temperature, Mean Barometric Pressure, 

 Mean Tension of Vapour, and Mean Gaseous Pressure at every 

 second hour. 



The sun is vertical at Bombay twice in the year, viz. in the middle 

 of May and towards the end of July. The rainy season sets in about 

 the commencement of June (in 1845 on the 2nd of June), and ter- 

 minates in August, but with heavy showers of no long duration con- 

 tinuing into September. During the rainy season, and in the month 

 of May which immediately precedes it, the sky is most commonly 

 covered with clouds, by which the heating of the earth by day, and 

 its cooling at night by radiation, are impeded, and the range of the 

 diurnal variation of the temperature is greatly lessened in compari- 

 son with what takes place at other times in the year. The strength 

 of the land and the sea breezes in those months is also comparatively 

 feeble, and on many days the alternation of land and sea breeze is 

 wholly wanting. During the months of November, December, Ja- 

 nuary and February, the diurnal range of the temperature is more than 

 twice as great as in the rainy season, and the land and sea breezes 

 prevail with the greatest regularity and force. 



In addition to the monthly tables, we may therefore advantage- 

 ously collect in one view, for purposes of contrast, the means of the 

 months of May, June, July and August, as the season when the sky 

 is generally clouded, — and of the months of November, December, 

 January and February, as the season of opposite character, when the 

 range of the diurnal temperature is greatest, and the land and sea 

 breezes alternate regularly, and blow with considerable strength. 

 These seasons are contrasted in Table II. 



If we direct our attention to the diurnal variations, commencing 

 with those of the temperature, we find them exhibiting a single pro- 

 gression, having a minimum at 18 h and a maximum at 2 h ; the ave- 

 rage difference between the temperature at 18 h and 2 h being 7 0, 77 



