34 Lieut.-Col. Sabine on some Points in 



ber, the latter season being that of the rains. The average degree 

 of humidity in the year is very slightly lower than either at Toronto 

 or at Greenwich, but is still closely approaching to a value expressing 

 the presence of three-fourths of the quantity of vapour required for 

 saturation. 



The mean gaseous pressure in 184-3, derived from the two-hourly 

 observations, appears to have been (29*023 + 0*025, an index cor- 

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

 the observations were made =) 29*048 English inches; or, mea- 

 sured by the height of a mercurial column in the latitude of 4-5°, 

 28*988. 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 

 observations at every second hour, appears to have been (29*803 

 + 0*025 = ) 29*828, or, with the correction applied for gravity, 

 29*768, the elevation being thirty-five feet above the sea. This is 

 less than what is generally received as the average height of the 

 barometer in the same latitude. From the careful comparison de- 

 scribed in Dr. Buist's report of the standard barometer with se- 

 veral other barometers, there seems great reason to believe that the 

 mean height shown by it must be a very near approximation at 

 least 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 November, December, January and February, 29*921. 

 The mean vapour pressure in the same seasons is respectively 0*904 

 and 0*623, and the gaseous pressure consequently 28*763 and 29*298. 

 There is therefore between the two seasons a difference of 0*535 in. 

 of gaseous pressure, and of 5°*84 of temperature ; the lowest pres- 

 sure corresponding to the highest temperature, and vice versa. If 

 we may allow ourselves to make a rough proportion drawn from a 

 single case, we may estimate a decrement of 0*1 in. of pressure to 

 an increment of 1° F. The highest temperature and lowest pressure 

 are accompanied for nearly the whole of the period by the southern 

 monsoon ; the lowest temperature and the highest pressure are ac- 

 companied by the northern monsoon. 



The curves of the annual variation of the gaseous, barometric, 

 and vapour pressures, which are represented in Plate I., show how 

 much of the influence produced on the gaseous pressure, by the al- 

 ternation of the overflow in the high regions of the atmosphere as 

 either side of the equator becomes heated in its turn, is masked in 

 the barometric curve by. the combination in the latter of the vapour 

 pressure, the variations of which take place throughout the year 



■wet thermometer at the same time as the harometer ; the register would also be 

 rendered much more complete by the addition of another observation-hour, about 

 6 a.m., which might not perhaps be inconvenient. The atmospheric pressure and 

 the tension of vapour at or near the coldest hour of the twenty-four, are important 

 data in meteorological discussions. 



