XXii APPENDIX. 
The barometer is generally higher at about 10 a.m. than at 11 p.M., the times before- 
mentioned, when it reaches its greatest height in the twenty-four hours; and it is lower 
at 5 p.m. than at 4 o’clock in the morning. 
It hence appears that the atmosphere is acted upon by an influence constantly and 
regularly operating during the year ; that it has its greatest density at about ten o’clock 
in the forenoon, diminishing till five in the afternoon, when it begins to regain what it 
had lost; and continues advancing towards its first state until about eleven o’clock at 
night, when it has nearly the same density as in the forenoon. The diminution of 
density again begins, and a like effect is produced by the disturbing power as in the 
day ; the atmosphere, however, is not affected in so great a degree as when the sun is 
above the horizon. 
As it seemed that the heights taken during the usual interval of observing meteorolo- 
gical instruments, generally between sun-rise and eight or nine P.M., were not those best 
calculated for the purpose of finding the exact mean: in order to ascertain what correc- 
tions should be applied on this account, the thermometer and hygrometer were also 
observed, with the barometer, every hour during the interval before stated; also the 
winds and weather, together with the phases of the moon for each month; the day of 
the nearest approach of the moon to the earth in the month; and the day of her greatest 
distance. These observations are also given in detail in the Madras Observatory 
Papers.* 
In the next Table are the heights of the barometer, thermometer, and hygrometer, 
taken from the ordinary diary on the days when the observations in the former Table 
were made, that is, the 10th, 20th, and 30th of each month; with the differences of the 
means of both sets of observations: these differences, contained in a supplementary 
table, are the corrections sought, and are applied to the daily means of the heights of 
the diary, as usually kept; asecond supplementary table contains the corrections for the 
monthly means, found by taking the means of the daily corrections, and are also applied 
to the monthly means of the diary. 
Madras is upon an open coast, and the time of the high-water at the Syzigies appears 
to be at 6h. 4m., the ebb and flow about six hours each way, with a rise and fall of 
little more than three feet. 
If the times of these tides of the atmosphere, as they may be termed, as shewn by 
the barometer, varied daily, like the times of the tides of the ocean, we might consider 
the moon as mainly instrumental in producing them; but occurring at nearly the same 
hours every day of the year, whatever may be the phases of the moon, or her position 
in her orbit, we must be contented with allowing that planet her ordinary influence. 
By selecting from the diary in 1823, for every hour the circumstances regarding the 
height and variation of the barometer with the winds and weather, and the position of 
the moon in her orbit, on days when the barometer was most likely to be affected by 
* Table beginning at page 374. 
