CANAL. 211 



the stream, and allowing it to run two miles an 

 hour, it discharges every day into the Dead Sea, 

 6,090,000 tons of water ; whereas this sea being 

 72 miles long and 18 broad, there will be drawn 

 up by evaporation S, 960, 000 tons, and this differ- 

 ence between the supply and the diminution must 

 be made good from some other source. Dr. Hal- 

 ley, upon a supposition that the Mediterranean 

 Sea covers 160 square degrees, infers that it must 

 lose in vapour in a summer's day at least 52S0 

 millions of tons, and that all the rivers which run 

 into it only furnish 1827 millions of tons in the 

 same period. Bishop Watson calculates, that 

 1600 gallons of water evaporate from an acre of 

 ground, in twelve hours' sun. Dr. Williams of 

 Vermont, says that an acre of ground, covered 

 with trees, throws out in twelve hours, 3875 gal- 

 lons of water ; and he further states that the 

 evaporation from a surface of land, covered with 

 trees and other vegetables, is one third greater 

 than from a surface of water. And he also asserts 

 that in Bradford, New England, the evaporation 

 amounted in 1772 to 42.6i inches. Dr. Dobson 

 states the yearly evaporation in Liverpool to be 

 36.78 inches. But the most accurate experiments 

 on this subject were made by Dalton, at Manches- 

 ter, for three years in succession : anil the mean 

 rain for that period was u3.55 inches annually j 



