EVAPORATION AT PALERMO. 



459 



tlien of the three elements, temperature, humidity, and force of the wind, 

 we establish with the data of the table, for the daily evaporation, 20 

 equations of condition, which being resolved by the method of least 

 squares yield the following normal equations : 



8.10 . t + 26.78 . h + 3.22 ./-1.63=0 ) 

 20.78 . t + 95.93 . h + 11.45 ./-5.33=0 [ . . . . (1.) 

 3.22 . t + 11.45 . h + 1.45 ./-0.65=0 ) 



wherein f, /«,/, are the coefficients of the temperature, humidity, and 

 force of the wind, to be determined. The equations (1) being resolved, 

 we obtain the following values : 



t= + 0.20675 

 h= + 0.01517 

 /= + 0.11006 

 which coefficients indicate that with the increase of the temperature 

 and force of the wind, the evaporation also augments, while it dimin- 

 ishes with the increase of the humidity, which, in effect, is also shown 

 by the actual review of each month. The formula, then, of the evapora- 

 tion, by the Yiveuot atmometer placed in the shade and defended from 

 the direct action of the wind, will be the folowiug : 



E=T . 0.20675-H . 0.01517+ F . 0.11006 

 in which T indicates the temperature in centesimal degrees, H the hu- 

 midity in hundredths of saturation, F the horary velocity of the wind 

 in kilometers. If, with this formula, we calculate the daily evaporation 

 for each of the twenty months under consideration, we obtain the fol- 

 lowing figures, which we transcribe, beside those resulting from obser- 

 vation, with the relative differences : 



Months. 



Evaporation 

 calculated. 



Evaporation 

 observed. 



Difference. 



1865. 



May 



June 



July 



August 



SeXitember 



October 



Kovember 



December 



1866. 



January 



February 



March 



April 



May 



Juue , 



Jnly , 



August 



September 



October 



November 



December 



MiUimeien 

 4. 024 

 5.144 

 5.485 

 5.317 

 4.847 

 4.269 

 3.246 

 2.257 



255 

 839 

 320 

 374 

 624 

 177 

 .526 

 054 

 244 

 696 

 094 

 574 



Millimeters. 

 3.394 

 4.719 

 5.113 

 5. 268 

 4.329 

 2.746 

 2.790 

 2.151 



2.492 



2. 819 

 3.906 

 3.847 

 4. 239 

 4.432 

 6. 905 

 5.918 

 4.089 



3. 493 

 3.211 

 2.314 



MiUimetei's, 



— 0. 630 



— 0.425 



— 0. 372 



— 0. 049 



— 0.518 



— 1.523 



— 0. 456 



— 0. 106 



+ 0.237 



— 0. 020 

 -f 0.586 

 + 0.473 

 + 0.615 

 + 0.255 

 + 1.370 

 -f- 0.864 



— 1. 155 



— 0. 203 

 + 0. 117 



— 0.260 



