some Experiments in Climatological Physiology. 337 



6. Evaporation Formula for Water in Tanks. 



The reality of this increase of evaporation through wind 

 is implied in the empirical formulae of Abbassia, Carpenter, 

 Fitzgerald, and Stelling, all of whom give for E the rate of 

 evaporation from an indefinitely large surface of water. 



E = *(/"-/"){l + *'V} J .... (8) 



in which/" is the vapour saturation-pressure of the surface 

 of the water, f" is the saturation-pressure for the dew-point, 

 and V denotes wind velocity. There is, however, no sort of 

 agreement among the constants given. 



As far back as 186 7 Tacchini gave a formula of the type 



E = aT-&/A + cV, (9) 



Y denoting velocity of wind ; and also further gave a 

 formula, 



E=aT-h'fjL + c'Y-dv + esmh, . . . (10) 



where v is the cloudiness in hundredths of the sky obscured,. 

 h is the meridian altitude of the sun *. 



A. "Weilemann in 1877 gave a formula which may be 

 written 



AM 



E= <^ (1+ * Y >' c 11 ) 



in which A and Ic are constants determined from observa- 

 tions ; V is wind velocity ; a is the change in the vapour- 

 tension of saturated air at the temperature of the experiment 

 for 1° C. ; M is the saturation-deficit (in grammes per cubic 

 metre) t- 



In 1885 F. Houdaille submitted a formula, viz. : — 



E ' = 1+W + 1 fo^l?-/) ( V + 5 ^) , • (12) 



in which E„ is the evaporation for velocity V ; E is the 

 evaporation in still air ; F and / are the differences of 

 the vapour saturation-pressure for the water temperature 

 and the vapour-pressure in the air %, in relation to the effect 

 of wind velocity, &c. 



* Bull. Met. Oss. iii. pp. 1-10, 17-19 (1867). 

 f Sclnceiz. met. Bebb. xii. pp. 268-368. 

 X Comptes Rendus, ci. pp. 428-431 (1885). 



