\IS6 ON KAIN, EVAPORATION, &C* 



colnfhire, Norfolk, Suffolk and Effex, from the Humber to 

 the Thames, though drawn from a country of 7000 fquare 

 miles, manifeftly fall far fhort of the Thames. The twq 

 places in this diftrict, for which we have accounts of the rain, 

 Norwich and Upminfter. give a mean of only 22f inches an- 

 nually. This, with the flatnefs of the country, which pre r 

 vents the water from running off in fome degree, makes the 

 rivers much Iefs than what might otherwife be expected from 

 the extent of ground. There are but three or four of any con- 

 fequence, Probably all the rivers may amount to half the 

 fize of the Thames. There remains above 6000 fquare miles 

 in Wales, from the Wye to the Dee, inclufive of the laft, and 

 the northern counties ofLancalter, Weftmoreland, Cumber- 

 land, Northumberland, and Durham, with part of Chelhire 

 and a fmall part of Yorklhire, from the Merfey round by the 

 Tweed to the Tees, amounting to 7 or 8000 fquare miles, to, 

 be eftimated. 

 The rivers upon Thefe two di virions, though not larger than fome others, 

 confideredas* abound in rivers, many of which are confiderable in magni- 

 carryingoffi3 tude and of great rapidity. The rains at an average, it is 

 in 6 C ^thdr°fall hC P robable ' are double what they are in the S.E. counties of the 

 annually. kingdom. The rivers in thefe two diftricts cannot fairly be 



eftimated, I think, at lefs than four times the Thames. It 

 appears, then, that by this eftimation, the water carried off 

 by all the rivers in England and Wales, may amount to nine 

 times that carried off by the Thames = 1 3 inches of rain. 

 There remains ftill fixteen times the water of the Thames, ox 

 23 inches of rain to account for, before we have difpofed of 

 all the rain and dew. 



SECTION 3. 



An EJlimate of the Quantity of Water raifed by Evaporation. 



Evaporation Upon looking over the furface of any country, three prin-r 



cipal varieties of furface prefent themfelves to view, as far as 



refpecls evaporation, namely, water, ground covered with 



grafs and other vegetables, and bare foil. The difficulties 



that occur in attempts to find the quantity of water evaporated 



in thofe three cafes, are perhaps the principal reafon why our 



knowledge on this head is fo imperfect. 



from water, bare -As far as experiments hitherto made authorife us to draw 



foil, and covered conclufions, it (hould feem that the evaporation from water is 



* ound ' greateft;; 



