

l70 «tf RAlfr, EVAPORATION, &C 



the year together, it is not fo in taking the months feverally, 



becaufe it prefumes that the earth in the veflel contains the 



fame quantity of water at the end of each month, or is fatu- 



rated with it ; whereas in the fummer months it is frequently 



fhort of faturation. The confequence is, that the evaporation 



appears from this table to be fomething lefs than it really is in 



the fummer months, and fomething more in the antumnal *. 



Conclufions. From thefe experiments it feems we may conclude— lft. 



ground'is 30 That the quantity of water evaporated, in the circumjlances 



inches. above related, amounts to 25 inches of rain annually ; to which 



if we add five inches for the dew, it will give 30 inches of 



water railed annually. 



It increafes with 2d. That the quantity of evaporation increafes with the 

 the ram. . t ^ . \i _, r , _. 



ram, but not proportionally. Thus, 1797 gave the molt rain 



and the greateft evaporation, &c. 



Deep bare foil 3d, That it does not appear there is much difference be- 



differ. twixt the evaporation from bare earth, when there is fufficient 



depth of foil, and that from ground covered with vegetating 



grafs. The account in 1796 is much what might have been 



expected, if the earth had been covered with grafs. 



Whether this As this account of evaporation, amounting to 30 inches, 



the rivers of 13, exceeds the medium referve of rain of 23 inches, it demands 



making 43 in- an enquiry whether the rain is adequate, or whether the earth 



rain ^indicate C ^ e " ves a Supply of water from fome fubterranean refervoir, 



another fupply ? according to the opinion of fome philofophers. 



With refpecl to the deficiency of 7 inches, there are three 



Reply j nega- caufes to be affigned for it, which appear to me fully fufficient, 



without having recourfe to any fource but that of rain for the 



fupply of the earth in general. 



The evapor. j ft. I n the account of the rain that patTed through the earth 



tie too great. * * n our evaporating veflel, there are a few monthly products 



marked, -f- thofe were occasioned by the bottle that received 



the water through the pipe being found with the water running 



oyer ; this lofs was placed to the account of evaporation ; it 



Could not be much, as the water was taken feveral times in a 



month, but poflibly might amount to one inch in the year. 



The rain at 2d. The rain at Manchefter, being 33§ inches annually, 



ceedsMie mc- " exceeds the medium pf 31 inches; and confequently, ac- 



* N. B. The earth in the vefTel always appeared as well fup- 

 plied with raoifture as the groun.d around it, in the drieft weather ? 



cording 



