ILLUSTEATED. 



wich, at each hour in the day for every month in the year. 



Now, I have assumed that the depression at one o'clock, 

 given for Greenwich, bears the same proportion to tlie 

 depression at one o'clock found from observation at Liver- 

 pool, that the mean depression given for Greenwich, does to 

 the mean depression required for Liverpool. The following 

 example will explain how the corrections for diurnal range 

 have been deduced. 



For instance, — 



For the Month of May, 1850, — 



The mean reading of the dry-bulb thermometer was 55*8°; 

 of the wet-bulb thermometer, 49*4°; and the mean daily range 

 of temperature was 10 '3°. 



By Glaisher's Table IV.,— 0.412 is the Factor for Oh. 48m. 

 local time, and — 0-412 x 10-3° = — 4'24° = the cor- 

 rection for diurnal range for the dry-bulb thermometer. 



From observation at Liverpool, 6*4° was the depression of 

 the , wet below the dry-bulb thermometer at Oh. 48m. local 

 time. From Glaisher''s Table Y., 5-88° is the depression for 

 the same local time at Greenwich, and 3*01° is the mean of 

 the twenty-four hourly depressions at Greenwich, therefore the 

 difference is 2*87° for Greenwich. 



Now, — = 3*12,° therefore, the correction for 



diurnal range for the wet-bulb thermometer = — 4*24° (the 

 correction for the dry-bulb), diminished by 3*12, or — 1*12°. 



I have been particular in describing how the mean tempera- 

 ture of the air from the dry-bulb thermometer, and the mean 

 temperature of evaporation from the wet-bulb thermometer 

 have been derived ; because any error in these determinations 

 must influence the whole of the hygrometrical deductions. 



In the accompanying tables, column 1 contains the month and 

 year to which the various results in the horizontal line opposite 

 170 



