the Meteorology of Bombay. 27 



bable ; it could not be expected that the influences of temperature 

 should always be so simple and direct as they appeared to be at To- 

 ronto ; and a more complex aspect of the phaenomena might parti- 

 cularly be looked for, where a juxtaposition should exist of columns 

 of air resting on surfaces differently affected by heat (as those of 

 land and sea), and possessing different retaining and radiating pro- 

 perties. In such localities within the tropics, the well-known regular 

 occurrence of land and sea breezes for many months of the year 

 made it obvious that a double progression in the diurnal variation 

 of the force of the wind must exist, and rendered it highly probable 

 that a double progression of the gaseous pressure would also be 

 found. It was therefore with great pleasure that I received, through 

 the kindness of Dr. Buist, a copy of the monthly abstracts of the 

 two-hourly meteorological observations, made under that gentle- 

 man's superintendence at the observatory at Bombay in the year 

 1843 ; accompanied by a copy of his meteorological report for that 

 year, possessing a particular value, in the full account which it gives 

 of the periodical variations of the wind, and in the means which it 

 thereby affords of explaining the diurnal variation of the gaseous 

 pressure. This pressure presents at Bombay an aspect at first sight 

 more complex than at the three above-named stations in the tempe- 

 rate zone, but I believe it to be equally traceable to variations of the 

 temperature, and to furnish a probable type of the variations at in- 

 tertropical stations similarly circumstanced in regard to the vicinity 

 of the sea. 



The observatory at Bombay is situated on the island of Colabah, 

 in N. lat. 18° 51' and E. long. 72° 50' at an elevation of thirty-five 

 feet above the level of the sea. In the copy of the observations re- 

 ceived from Dr. Buist, the monthly abstracts are given separately 

 for each month, of the standard thermometer, — of the wet thermo- 

 meter, and of its depression below the dry, — and of the barometer. 

 In Table 1. 1 have brought in one view the thermometrical and baro- 

 metrical means at every second hour, and the mean tension of the 

 vapour and mean gaseous pressure 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 thermometer 

 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 ob- 

 tained been taken as the value corresponding to the hour. The dif- 

 ference is however so small, that for the present purpose it may be 

 regarded as quite insignificant. 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 present concerned, would be 

 scarcely sensibly affected. The pressures of the dry air (or the ga- 

 seous pressures) are obtained by deducting the tension of the vapour 

 from the whole barometric pressure. 



