826 A Differiation on Ihs 



The nine rivers, therefore, difcharge into the MedJter- 

 ranean 1,827,000,000 tons of water in a day ; which is 

 but little more than a third of what is railed from its 

 surface in the fame time, by evaporation. 



The above eftimate of the water of the Thames is 

 profelTedly overrated, and has fince been found, by Mr. 

 Dalton the Philofopher of Manchefter, to be about one 

 third two large. Reducing the nine rivers in this pro- 

 portion, we Ihall find that their daily difcharge is only 

 1,218,000,000 tons This is rather lefs than l-4th of 

 the quantity evaporated from that sea ; and leaves 

 4,062,000,000 tons, or 3-4ths of the whole, to meet the 

 evaporation from that immenfe region, by which thefe 

 rivers and their branches are fupplied. 



From a feries of obfervations refpecling the annual 

 fupply of rain, made at 31 different flations in England, 

 during different periods of from 1 to 21 years, Mr. 

 Dalton finds the average quantity for the whole of 

 England and Wales to be 31 inches. To this he adds 5 

 inches for dew ; making a total of 36 inches or three 

 feet. After a minute examination of the rivers of thofe 

 two countries, he eflimates their whole annual dis- 

 charge to be nine times that of the Thames. Allowing 

 this calctilation to be correct, the rivers will exhaufl on- 

 ly 13 inches of rain; leaving '23 inches to evaporate 

 from the land : a refiduum, which he finds, by a num- 

 ber of experiments, to be amply fufEcient. 



The quantity of rain, which falls in our own country,^ 

 is believed to be confiderably greater than that in any 

 country of Europe. The exadl amount however can- 

 not, at prefent, be Hated with precifion ; as few gentle-' 

 men have hitherto made the requifite obfervations. I 

 can only obferve, that I have feen various regifters of 

 rain kept at different places for confiderable periods ; 

 and the average refults of a ftill larger number. From 

 thefe I am led to conclude, that the quantity of water, 

 which annually falls in rain fnow and hail, will average 

 45 inches. To this ihould be added 5 inches, at leaft, 

 for dew ; making the v^^hole 50 inches. The United 



