76 REPORT—1845. 
are at present concerned, would be scarcely sensibly affected. The pressures 
of the dry air (or the gaseous pressures) are obtained by deducting the ten- 
sion of the vapour from the whole barometric pressure. 
Tas_te I. 
Bombay, 1843.—Mean Temperature, Mean Barometric Pressure, Mean Ten- 
sion of Vapour, and Mean Gaseous Pressure at every second hour. 
Hours of Mean Bombay Tension of Gaseous 
aa A 1 — Temperature. | Barometer. Vapour. Preemie! 
i in. in. in. 
18 78-4 29-805 0:750 29°055 
20 79°6 29-840 0:766 29:074 
22 81:8 29°852 0-771 29-081 
0 83:2 29°817 0-768 29-049 
2 84:1 29°776 0°795 28-981 
4 83:9 29°755 0-800 28-955 
6 82:3 29°74 0-802 28:972 
8 81:2 29-806 0801 29-005 
10 80°3 29°825 0:780 29°045 
12 79'8 29°809 0-775 29-034 
14 79°4 29°786 0-766 29-020 
16 73:9 29:778 0:761 29:017 
Mean of the year ...| 81:1 29:802 6-780 29-022 
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 commence- 
ment of June (in 1843 on the 2nd of June), and terminates in August, but 
with heavy showers of no long duration continuing 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 com- 
parison 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. Du- 
ring the months of November, December, January 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 advantageously 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, wheu 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 progression, having a 
minimum at 18" and a maximum at 2"; the average difference between the 
temperature at 18" and 2" being 7°77 in the clear season, 3°71 in the clouded 
season, and 5°°7 on the mean of the whole year. 
When however we direct our attention to the gaseous pressure, we perceive, 
very distinctly marked, the characters of a double progression, having one 
maximum at 10" and another at 22"; one minimum at 4° and another at 16%. 
