l844.]/r.- a paper read before the British Association 1845.109 



The Observatory at Bombay is situated on the island of Colabah in N. 

 lat. 18° 54', and E. long. 72° 50', at an elevation of 35 feet above th$ 

 level of the sea. In the copy of the observations received from Dr. Buist 

 the monthly abstracts are given separately for each month, of the stand- 

 ard thermometer ; of the wet thermometer, and of its depression below 

 the dry j and of the barometer. In Table 1. I have brought in one view 

 the thermometrical and barometrical means of the observations at every 

 second hour, and the mean tension of the vapour and mean gaseous pres- 

 sure at the same hours. 



The tension of the vapour at the' several observation-hours has been 

 computed from the monthly means, at the same hours, of the wet ther- 

 mometer, and of its depression below the dry thermometer. The values 

 are consequently somewhat less than they would have been, had the ten- 

 sion been computed from each individual observation of the wet and dry 

 thermometers, and had the mean of the tensions thus obtained been taken 

 as the value corresponding to the hour. The difference is, however, so 

 small, that for the present purpose it may be regarded as quite insignifi- 

 cant. It would not amount in a single instance to the hundredth part of 

 an inch ; and as in every instance the difference would be in the same 

 direction, the relative values, which are those with which we are at pre- 

 sent concerned, would be scarcely sensibly affected. The pressures of the 

 dry air (or the gaseous pressures) are obtained by deducting the tension 

 of the vapour from the whole barometric pressure. 



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 1843 on the 2d 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 cloud, by 

 which the heating of the earth by day, and its cooling at night by radi- 

 ation, are impeded, and the range of the diurnal variation of the tem- 

 perature is greatly lessened in comparison 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, 

 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. 



