458 



METEOROLOGY. 



Tahle of the elements tcliicli have been enqyloyed in the researches on evapo- 

 ration., as observed with the Vivenot atmometer, transcribed from tlie 

 monthly bulletins. 



From tlie above table it will at once be perceived that tbe prime pro- 

 ductive cause of evaporation is the temiierature, the action of which 

 may be promoted by the force of the wind and impeded by the humidity. 

 If, therefore, we consider the quantity of evaporated water in relation 

 alone to the temperature as the sole cause, we may deduce the equation — 



390.8^ = 78.175 

 whence — 



t = + 0.20004 



If then the heat alone were the evaporating force, by multiplying the 

 mean daily temperature by the coefficient we should have the quantity 

 of the evaporation in millimeters. By making this calculation for the 

 months from the preceding table, and considering the differences between 

 the observation and the calculation, it will be seen that, in 18G5, the 

 greatest differences are met with in the months of May and October, in 

 which there occur two maxima of humidity, and that at that time 

 the evaporation observed is less than that calculated ; and, in 18(36, the 

 greatest differences are observed in tlie mouths of March, July, and 

 August, in which there occur minima of humidity and an increase in 

 the force of the wind, so that the observed evaporations become in these 

 months greater than those calculated. Hence the influence of the force 

 of the wind and of the humidity of the air is manifest. Taking account 



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