106 



[No. 31 



X* — Meteorology of Bombay, by Colonel Sabine, from a 

 <r a paper read before the British Association 1845. 



In a communication which I had the honour to make to the section at 

 the last meeting of the British Association, on the subject of the mete- 

 orological observations made at Toronto in Canada in the years 1840 to 

 1842, I noticed some of the advantages which were likely to result to the 

 science of meteorology from the resolution of the barometric pressure in- 

 to its two constituents of aqueous and of gaseous pressure. It was shewn, 

 that when the constituents of the barometric pressure at Toronto were 

 thus disengaged from each other and presented separately, their annual 

 and diurnal variations exhibited a very striking and instructive accordance 

 with the annual and diurnal variations of the temperature. The charac- 

 teristic features of the several variations, when projected in curves, were 

 seen to be the same, consisting in all cases of a single progression, having 

 one ascending and one descending branch ; the epochs of maxima and 

 minima of the pressures being the same, or very nearly the same, with 

 those of the maxima and minima of temperature, and the correspondence 

 121 other respects being such as to manifest the existence of a very inti- 

 mate connexion between the periodical variations of the temperature and 

 those of the elastic forces of the air and vapour. The curve of gaseous 

 pressure was inverse in respect to the other two ; that is to say, as the 

 temperature increased, the elastic force of the vapour increased also, but 

 that of the air diminished, and vice versa ; and this was the case both in 

 the annual and the diurnal variations. 



Such being the facts, I endeavoured to shew, in the case of the diurnal 

 variations, that the correspondence of the phenomena of the temperature 

 and gaseous pressure might 1 be explained, in accordance with principles 

 which had been long and universally admitted in the interpretation of 

 other meteorological phenomena, by the supposition of an extension in 

 height and consequent overflow in the higher regions of the atmosphere, 

 of the column of air over the place of observation during the hours of the 

 day when the surface of the earth was gaining heat by radiation, and by 

 the contraction of the column during the remaining hours when the tem- 

 perature was diminishing, and by its consequent reception of the overflow 

 from other portions of the atmosphere, which, in their turn, had become 

 heated and elongated. 



According to this explanation, there should exist, during the hours of 

 the day when the temperature is increasing, 1st, an ascending current at 

 the place of observation, of which the strength should be measured by 



