xxxu 



being duly corrected to the usual standard temperature of 32 Fahrenheit, 

 the Barometer reads highest in January, and lowest in June ; which are res- 

 pectively the coolest and hottest months in the year. As at all other tropi- 

 cal stations, the diurnal variations of the Barometer are here found to be so 

 regular in their recurrence, that there are very few days in the year on which 

 the atmospheric tides are not plainly discernible. The highest readings occur 

 about 9J A. M. The mercury then commences falling, and arrives at its 

 lowest minimum a little before 4 P. M, The secondary maximum and mini- 

 mum occur during the night, at 10 P. M. and 3J A. K. respectively, but are far 

 less marked than those observed during the day. The greatest daily range 

 occurs in March, and the least in December. The mean temperature, 

 although somewhat higher at Madras than at many other parts of the Presi- 

 dency, is subject to such small changes, that the severe extremes which else- 

 where prove so prejudicial to health are never experienced. 



The Dew Point, or Temperature at which rain would begin to fall if the air 

 were suddenly cooled down thereto, does not rise and fall conformably to the 

 temperature; for though its greatest depression below the Dry Bulb (13 '2), 

 occurs during the hottest month, June, the least difference (6 -6) falls in 

 October, when the temperature nearly agrees with the average of the whole 

 year. The per-centage of Humidity changes but slightly ; the average amount 

 of aqueous vapour in the atmosphere being exactly three-fourths of the whole 

 quantity sustainable thereby. The average Bain-fall is deduced from obser- 

 vations extending over a period of fifty-two years, viz., from 1804 to 1807, 

 and again from 1813 to 1860. The dryest year on record was 1832, when 

 only 18 J inches of rain were collected: the greatest quantity fell in 1827, 

 when nearly 89 inches were recorded. In October 1857, not less than 37f 

 inches fell; while no shower occurred throughout the first five months of 1860. 

 By summing up separate portions of this column, it will be found, that under 

 ordinary circumstances only about a tenth part of the year's rain falls during 

 the first five months, but a full half at the setting in of the N. E. Monsoon, in 

 October and November. It is also worthy of remark, that, whereas in Europe, 

 a rain gauge placed on the ground invariably collects more than one elevated, 

 some forty or fifty feet, in India the case is reversed. The difference is slight, 

 but the upper gauge receives more than the lower one. 



As regards the Wind nothing very definite can yet be pronounced, in con- 

 sequence of the imperfect instrumental registration employed, which has 



