INTHOM'CTION. 



XLT 



Like the curve which will represent changes in the temperature of the atmosphere daring a 

 day, that, also, by which fluctuations in the n l.itivc humidity may be shown consuls of but s> 

 single progression. As its maximum departure from the axis coincides with the hour of the 

 day when we find the minimum temperature, and vice versa, these periods vary with the sev- 

 eral months, but in the average of the year the first falls nearest to 6 A. M., and the last near- 

 est to 3 P. M. 



In the several months we find that the atmosphere approaches nearest to saturation in June, 

 and is driest in February, the increase of relative humidity being regular from February to June, 

 and the decrease uniform from June to February. These months likewise exhibit the greatest 

 and least diurnal ranges. 



The following table, containing the difference between the readings of the dry and wet 

 thermometers at each hour of the day, will show these facts more clearly : 



TABLE XIII. 



Excess of the mean temperature of the air at every hour of the day, above the mean temperature 

 of evaporation at the same hour, as shown by the term-day observations. 



a One observation. 



4 Two observations. 



c Four observation*. 



