On Rain, Evaporation, Sc. 352 
§ 2. 
An Estimate of the Quantity of Water that flows into 
the Sea from England and Wales in a Year. 
To calculate the quantity of water that flows 
down any one river into the sea in a given 
time, seems at first view a question of great 
difficulty. The necessary data, however, may 
be obtained with considerable exactness, by 
proper observations, and then it becomes an 
easy case of mensuration. Dr. Hutton, in his 
Philos. and-Mathemat. Dictionary, article River, 
proposes a very good method to determine by 
experiment the velocity of a river:—A cylin- 
drical piece of light wood, its length somewhat 
less than the depth of the waters, is to be taken, 
and a few small weights attached to one end in . 
order to make it swim upright. To the other - 
end a small rod is fixed in the centre in direction 
of the axis.—This being suffered to float down 
the stream will move with the’ velocity of the 
water; and if the rod be observed to incline 
towards the river upward or downward, it shews 
the current to be more rapid at the bottom or 
surface respectively. ! 
This experiment being made in iii middle 
and near the sides of a river, a medium velocity. 
may be obtained. Then the medium, breadth, 
depth, and space run over in a certain time 
