- 
ON SOME POINTS IN THE METEOROLOGY OF BOMBAY. 79 
Greenwich, and is similarly explained: the second minimum, which does not 
take place at the three above-named stations, is owing to the juxtaposition of 
the columns of air over the sea and land, which differ in temperature, and 
therefore in density and height, in consequence of their resting respectively 
on surfaces which,are differently affected by heat. 
The Plate shows the curve of the gaseous pressure, and the curve of the 
elastic force of the vapour; and between them is placed a diagram illustrating 
the hours of prevalence and of the greatest strength of the land and sea 
breezes. At Toronto and at Greenwich the diurnal curve of the vapour is 
a single progression, having its maximum at or near the hottest hour of the 
day, and its minimum at or near the coldest hour. We perceive in the Plate 
which represents the phenomena at Bombay, the modification which takes 
place in consequence of the supply of vapour brought in by the sea breeze 
continuing until a late hour in the evening, and prolonging the period during 
which the tension is at or near its maximum. ‘The minimum occurs as usual 
at or near the hour of the coldest temperature. 
If, then, the explanation which I have offered to the Section, of the physical 
causes which produce the diurnal variation of the gaseous pressure at Bom- 
bay, be correct, the diurnal variation of the barometric pressure occurring 
there is also explained, since it is simply the combination of the two elastic 
forces of the air and of the vapour. 
The solution of the problem of the diurnal variation of the barometer is 
therefore obtained by the resolution of the barometric pressure into its con- 
stituent pressures of vapour and air; since the physical causes of the diurnal 
variation of the component pressures have been respectively traced to the 
variations of temperature produced in the twenty-four hours by the earth’s 
revolution on its axis, and to the different proper ‘ties possessed by the mate- 
rial bodies at the surface of the globe in respect to the reception, conveyance, 
and radiation of heat. 
Annual variation—We now proceed to the annual variations, which are 
shown in the subjoined table. 
Taste III. 
| Monthly Means greater (+) or less 
ce) (—) than the Annual Means. 
1843, Tempera-| Vapour | Gaseous Barometer. ‘9 
ture. Pressure. | Pressure. 5 |Tempera-{| Vapour | Gaseous 
x ture. Pressure. | Pressure. 
January 76-4 | 0578 | 29-352 | 29:930 | 67 | —47 | —6-202 | +6329 
February 777 0648 | 29-246 | 29894 | 71 | —3-4 | —0-132 | +0:223 
March ...... 79:7 0-710 | 29:128 | 29-8388 | 74) —1:4 | —0-070 | +0:105 
April ......| 84:2 0°853 | 28-961 | 29:814 | 76] +3:1 | +0073 | —0-062 
May 0.0.40. 85-9 | 0-921 | 28-743 | 29-664 | 78) +4:8 | +0-141 | —0-280 
June......... 85:4 0:935 | 28:718 | 29653 | 80} +43 |+40:155 | —0:305 
Wenig 8025: 82:1 | 0896 | 28-737 | 29-633 | 85 | 11-0 |+0-116 | —0-286 
August ...... 81:2 0:859 | 28869 | 29°728 | 84) +0-1 0:079 | —0:154 
September..| 81:1 0:859 | 28:920 | 29:779 | 84 0-0 |-+0:079 | —0:103 
October ...| 822 | 0819 | 29-096 | 29-845 | 78 | +1:1 | -+0-039 | 0-003 
November..| 805 | 0-675 | 29-213 | 29-888 | 67| —0:6 | —0-105 | +0-190 
December..| 76:6 | 0592 | 29368 | 29-960 | 67| —4:5 | —0-188 | 10-345 
81:1 0:780 | 29:023 | 29:803 | 76 
We here perceive that the leading features of the phenomena ar clearly 
analogous to those which have been seen to present themselyes at Pay 
