EXPLANATIONS. 



belong ; column 2, the mean reading of the barometer, corrected 

 for index-error and reduced to 32° of Fahrenheit ; columns 

 3 and 5, the highest and lowest readings of the barometer for 

 each month and year ; and 4 and 6, the days on which they 

 occurred : these readings have been corrected for index-error, and 

 reduced to 32° of Falurenheit ; column 7 contains the extreme 

 range of the barometer during each month and year; column 8, 

 the mean pressure of dry air at the level of the sea: this 

 result is obtained from column 2, by adding the reduction to 

 the sea level, and subtracting the numbers found in column 

 29, which represent that portion of atmospheric pressure due 

 to water; column 9 shews the mean temperature of the air 

 deduced from the dry-bulb thermometer, combined with that 

 deduced from the maximum and minimum thermometers, after 

 correcting the readings for index-error and diurnal range as 

 before described; column 10 shews the mean daily range of 

 the thermometer for each month and year; columns 11 and 

 13 contain the highest and lowest readings of the thermometer 

 for each month and year ; and 12 and 14 the days on wliich 

 they occurred; column 15 shews the extreme range of tem- 

 perature during each month and year ; column 16, the amount 

 of rain collected in a gauge 25 feet above the ground ; 

 and 17, the number of days on wliich it fell; columns 18 to 

 25 shew the direction of the wind referred to eight points of 

 the compass — the letters at the top of the columns represent 

 the direction, and the figures shew the number of days in 

 each month and year that the wind blew from that direction ; 

 column 26 shews the estimated force of the wind, on the 

 assumption that a calm is represented by 0, and the greatest 

 gale by 6 : it has been found that the squares of the numbers 

 thus estimated represent the pressure in pounds on the 

 square foot very nearly;" column 27 shews the estimated 

 amount of cloud, on the assumption that represents a clear 

 sky, and 10 a cloudy sky ; columns 28 to 34 have been calcu- 

 lated by the aid of Mr. Glaisher's Hygrometrical Tables, 



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