210 



CANAL. 



cataract, and masses on the bank of the precipice, 



protruding from the summit of the cataract over 



the yawning gulf. 



1 



LETTER XLV1II. 



Western Region, September, 1820. 

 My Dear Sir, 



It Iras been found that the loss of water in the 

 canal exceeds the original estimate. Whether 

 this is most owing to soakage, leakage, or to the 

 power of evaporation, may be a subject of contro- 

 versy. I am inclined to believe that in all these 

 respects the diminution has been greater than 

 was anticipated. While the former will cease to 

 operate, in proportion as the canal is rendered 

 more impermeable and tight, the latter must con- 

 tinue with the duration of the world. 



Many calculations and experiments have been 

 made, at varrous times, to determine the quantity 

 of rain and quantity of evaporation in different 

 parts of the world. Dr. Halley estimated that 

 6914 tons of water are evaporated from every 

 square mile of the sea in a day ; and Dr. Shaw 

 has applied this estimate to the Dead Sea, and 

 considering the river Jordan about thirty yards 

 T*ide 7 and taking three feet for t,he mean depth of 



