On Rain, Evaporation, &c. 987 
remains above 6000 square miles in Wales, from 
the Wye to the Dee, inclusive of the last, and 
the northern counties of Lancaster, Westmor- 
land, Cumberland, Northumberland, and Dur- 
ham, with part of Cheshire and a small part of 
Yorkshire, from the Mersey round by the 
Tweed to the Tees, amounting to 7 or 8000 
square miles, to be estimated. 
These two divisions, though not larger than 
some others, abound in rivers, many of which 
are considerable in magnitude and of great ra- 
pidity. The rains at an average, it is probable, 
are double what they areinthe S. E. counties of 
the kingdom. The rivers in these two districts 
cannot fairly be estimated, I think, at less than 
four times the Thames.—lIt appears, then, that 
by this estimation, the water carried off by all 
the rivers in England. and Wales, may amount 
to. nine times that carried off by the Thames 
13, inches of rain. There remains still sixteen 
times the water of the Thames, or 29 inches of 
rain to account for, before we have disposed of 
all the rain and dew. 
§ 3. 
An; Estimate of the Quantity of Water raised by 
Evaporation. 
Upon looking over the surface of any 
country, three principal varieties of surface pre- 
