464 



METEOROLOGY. 



Month. 



1865. 



Calculated. 



Observed. 



O— C. 



Calculated. 



Observed. 



O— C. 



iTannary ... 

 rebrnary . . 



March 



April .• 



May 



Julie 



July 



AuECiist 



September . 



October 



November . 

 December.. 



Millimeters. 



Millimeters. 



Millimeters. 



5.466 



7. too 



8. 8-23 

 8. 345 

 7.105 

 4.701 

 2.666 

 0.935 



5. 753 

 7. 074 

 7. 977 

 7. 490 



6. 00-J 

 3. 504 

 2. 751 

 1. 9-28 



+ 0. 2o7 

 -0. 816 

 -0.840 

 -0. 855 

 -1.103 

 -1.177 

 + 0.085 

 + 0.993 



Millimeters. 

 1.689 

 3.700 

 4. 3-27 

 4. 992 



4. 599 

 6.093 

 9. 465 

 7. 846 



5. 373 

 3.521 

 3.404 

 2. 591 



Millimeters. 

 2.209 

 3. 1.59 

 4.974 

 5. 833 

 5.568 

 6.232 

 8. 911 

 7.547 

 5. 002 

 3. 236 

 2.863 

 2.495 



Millimeters. 

 + 0.520 

 -0. 007 

 + 0.647 

 + 0.841 

 + 0.909 

 + 0.139 

 -0. 554 

 -0. 299 

 -0.371 

 -0. 2:5 

 -0. 541 

 -0. 006 



From the differences it is seen that the results obtained by this in- 

 strument also are sufficiently exact to be capable of being approxi- 

 mately represented witb the special formula, and the accord between 

 the calculation and the observation seems to us satisfactory, regard 

 being had to the construction and conditions of situation of this appa- 

 ratus. 



The daily mean thus calculated from the elements of the twenty 

 months gives a result equal to S^'^.loG, while the observed mean was 

 5mm_Q27j whence we have the difference, 0™™.129, so that the total 

 evaporation as calculated for the twenty months is found to be equal to 

 3,145™™.1G, and the sum of the evaporation observed 3,071"™.21— dif- 

 ference, 73'"™.95. 



The daily mean, as calculated for 18G6, gives a result of 4™™.7S52, 

 and the total in the twelve months, IjTiG^^'.GO, while the observed was 

 1,7G9'"'^.49— difierence, 22°"^.89. 



Knowing, therefore, the mean force of the wind, the mean humidity, 

 and at the same time the clearness and temperature, w^e shall be in a 

 position to verify approximately the mean monthly and annual evapo- 

 ration by this atmometer exposed to the direct action of the wind and 

 rays of the sun. "VVe have not all these elements, and hence cannot at 

 present apply the formula in its entirety. But, for a first approxima- 

 tion, we may take account solely of the temperature, humidity, and alti- 

 tude of the sun, having the coefficients of the force of the wind and vol- 

 ume of the clouds contrary signs; in effect, thus calculated the evapora- 

 tion for 18GG results differently from that observed, w^hich was 1,7G9''^.0 

 by only SG^'^.O. 



By making the calculation, with the relative humidity transcribed 

 from the only decennium in which psychrometrical observations were 

 conducted, the evaporation in the open air yields the results denoted in 

 the following table, as well for the daily mean as for the total of each 

 mouth and each season, together with the annual* mean : 



