4G0 METEOROLOGY. 



Hence it would appear that if the daily evaporation be calculated in 

 this way we incur the risk of an error of ± 0™"".0 ; and although this 

 difference may seem considerable, yet, taking into account the small 

 number of observations, and the anomalies which ordinarily occur in 

 this element, as well as the excesses of the weather experienced in the 

 two years of the observations, it will be seen that the variations in the 

 evaporation are distinctly represented. 



If the daily mean be thus calculated from the total of the twenty months, 

 with T = 19°.54, H = G9.13 and F = 8.31, 



It will be found = 3°>. 913 



And the mean of the observed evaporation 3™. 9L'4 



Difference = O'". Oil 



So that the total of the calculated evaporation for the twenty 



months is found = 2386'".93 



While that from observation 2393°^. 78 



Whence the difference = C™.85 



As a proof of the manner in which this formula may represent the 

 course of the daily evaporation, we have calculated it for each day of 

 the month of October, 18GG, selecting this mouth for its variety in the 

 different elements, so that the evaporation does not proceed directly in 

 accordance with any of the curves of these elements. 

 Tlie sum of the daily evaporations calculated for every day 



of this month gives a total of 113°^™.34 



While the observed amount was 108™™.29 



Whence results a difference only of 5'"'".05 



And from the course of the evaporation we have constructed the curves 

 of evaporation as observed and calculated, which will be found in the 

 annexed table, and which clearly demonstrate their conformity ; thus 

 proving the distinct exactness of the formula and the excellence of the 

 instrument in its sensibility to the variations of the different elements 

 which concur in the production of evaporation. 



It is not at i)resent possible to establish the exact ratio of the evapo- 

 ration in the different seasons and months, because the proper elements 

 are wanting. In regard to the meteorological year 1865- 06, we have 

 the evaporation distributed in the following manner : 



Millimeters. 



Winter 228.65 



Spring 367.90 



Summer . . 530.47 



Autumn 327.36 



