1844.]/r; a paper read before the British Association 1845. 115 



serrations, appears to have been 29 024-30 025 (an index correction which 

 Dr. Buist gives as that of the barometer with which the observations 

 were made) =29-048 English inches. The height above the sea is thirty- 

 five feet, and the latitude 19° N. 



The mean height of the barometer in the year 1843, derived from ob- 

 servations at every second hour, appears to have been 29-803 ; the ele- 

 vation being thirty-five feet above the sea. This is less than wha') is ge- 

 nerally received as the average height of the barometer in the same lati- 

 tude. From the careful comparison described in Dr. Buist's report as 

 having been made of the standard barometer with several other barome- 

 ters, there seems great reason to believe that the mean height shewn by 

 it must be a near approximation to the true mean atmospheric pressure 

 in the year 1843 at Bombay. 



The mean height of the barometer in the four clouded months of May, 

 June> July, and August, is 29-667 ; and in the four clear months of No- 

 vember, December, January, and February, 29-921. The mean vapour- 

 pressure in the same seasons is respectively 0-904 and 0*622, and the gase- 

 ous pressure consequently 28-760 and 29-298. There is, therefore, a dif- 

 ference of 0-535 of gaseous pressure in these two seasons, and there is al- 

 so a mean difference of temperature of 5.84° degrees. The lowest pres- 

 sure corresponds to the highest temperature, and vice versa: if we may 

 allow ourselves to make a rough proportion drawn in a single case, we 

 may estimate a decrement of 0*1 inch of pressure to an increment of 1 Fah- 

 ren-heit. The highest temperature and lowest pressure is accompanied 

 for nearly the whole of its period by the S. W. monsoon, or a wind blowing 

 from the sea. The lowest temperature and the highest pressure is ac- 

 companied by the N. E. monsoon, or a wind from the land. The differ- 

 ence of the gaseous pressure in the two seasons is partially marked in 

 the barometer by an opposite difference in the tension of the vapour, so 

 that the barometric difference between the two seasons, though still dis- 

 tinctly manifest, is less than the difference of gaseous pressure. 



The analogy of the annual and diurnal variations, considered in respect 

 to the explanation which has been attempted of the latter, is too obvious 

 to be dwelt upon. The decreased gaseous pressure in the hot season is 

 occasioned by the rarefaction of the air over the land whilst the sun is in 

 the northern signs, and its consequent overflow in the higher regions, pro- 

 ducing a return-current in the lower strata ; and the increased pressure 

 in the cold season is occasioned by the cooling and condensation of the 

 air whilst the sun is on the south side of the equinoctial, and its con- 

 sequent reception of the overflow in the upper strata fronf the regions 



