WITH THE SALT WATER OF THE SEA. 513 
Even to navigators, an acquaintance with this subject may 
sometimes be of use. Thus, for example, when entering a 
creek in an unknown coast, they may easily ascertain whether 
any streams of fresh water flow into it, by examining the com- 
parative density of the water taken from the surface and from 
below. 
These experiments appear to give countenance to the opi- 
nion which supposes that the water at the surface of the sea 
contains less salt than the water at the bottom. This may be 
expected to take place in the neighbourhood of continents, at - 
least, whatever may be the case in the open ocean. During 
winter, the difference is probably very considerable, as at that 
season the rivers incessantly pour vast quantities of fresh wa- 
ter into this great reservoir, while but a small portion is ab- 
stracted by evaporation. In the Frith of Forth, the difference 
between the dense water of summer and the diluted water of 
the winter season, is as eighteen to sixteen, and that even as. 
_ far down as Prestonpans. 
Manse oF FLIsx, 
11th March 1816. } 
XXIV, 
