Ya7i Yea7i Reservoi7\ 



177 



where the rauifall is much greater than in the south of 

 England, and the general temperature and atmospheric 

 influences less favourable for the promotion of evaporation^ the 

 latter has been found by the Engineer of the Paisley Water- 

 works and others to be less than in the southern counties of 

 Great Britain. 



In the following table I have placed in juxta position the 

 results arrived at by different observers. 



Authority, 



Locality. 



Mean 

 annual 

 rainfall. 



Kvap oration 

 from surface 

 or difference 

 between rain- 

 fall and avail- 

 able supply. 





Ferrybridge 



24: b 



19'72 



Dalton 



Manchester 



33-56 



2515 



Howard 





36- 



30*47 



Thorn 



Paisley 



54- 



18* 



Beardmore 



Bute 



45-4 



22-5 : 



Ditto 



Bivington Pike 



55-5 



31-3 



Dickenson 

 Charnock 



Ditto 

 Dalton 



Ferrybridge 

 Ditto 



Manchester 



26-6 



15-64 

 32-60 

 35-03 

 4443 ' 



Remarks on nature of sur- 

 face to whicli the observa- 

 tions refer. 



Porous well drained soil 

 5 Ordinary mould with 

 c vegetation on surface. 

 I General surface of 

 V Gt. Britain. 

 I Small gathering grnd 

 Ipossessingwell drain- 

 Jed surface, wateredby 

 ^numerous catch-water 



drains. 

 Low country, 

 r Elevated district, 

 1 1545 ft. above sea. 



The inferences to be derived from an inspection of this 

 table are, — firsts that the values assigned to evaporation from 

 land surfaces by these different authorities are, (with the 

 exception of that given by Dickenson), quite compatible with 

 each other if due allowance be made for the variations of the 

 temperature, geological configuration, soil, and rainfall of the 

 places of observation : and, secondly, — that when the annual 

 rainfall exceeds the annual average quantity, the annual pro- 

 portionate amount thereof evaporated does not also increase as a 

 necessary consequence of such augmented rainfall, I may here 

 remark that Charnock's observations indicated at the least 

 annual evaporation during the five years over which his ob- 

 servations extended, had occurred during a year w^hen the 

 annual rainfall had been about the average of the five years. 

 This shows the futility of assuming (as too frequently has 



